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Immanuel Kant: Have the courage to use your own understanding. Enlightenment is man’s emergence from his self-imposed nonage. Nonage is the inability to use one’s own understanding without another’s guidance. Act only according to that maxim whereby you can, at the same time, will that it should become a universal law. Guarantee for Perpetual Peace: The Law of Nations Shall be Founded on a Federation of Free States. The Law of World Citizenship Shall Be Limited to Conditions of Universal Hospitality.

April 25, 2013

Immanuel Kant

What Is Enlightenment? 
Immanuel Kant 1

Enlightenment is man’s emergence from his self-imposed nonage. Nonage is the inability to use one’s own understanding without another’s guidance. This nonage is self-imposed if its cause lies not in lack of understanding but in indecision and lack of courage to use one’s own mind without another’s guidance. Dare to know! (Sapere aude.) “Have the courage to use your own understanding,” is therefore the motto of the enlightenment.

Laziness and cowardice are the reasons why such a large part of mankind gladly remain minors all their lives, long after nature has freed them from external guidance. They are the reasons why it is so easy for others to set themselves up as guardians. It is so comfortable to be a minor. If I have a book that thinks for me, a pastor who acts as my conscience, a physician who prescribes my diet, and so on–then I have no need to exert myself. I have no need to think, if only I can pay; others will take care of that disagreeable business for me. Those guardians who have kindly taken supervision upon themselves see to it that the overwhelming majority of mankind–among them the entire fair sex–should consider the step to maturity, not only as hard, but as extremely dangerous. First, these guardians make their domestic cattle stupid and carefully prevent the docile creatures from taking a single step without the leading-strings to which they have fastened them. Then they show them the danger that would threaten them if they should try to walk by themselves. Now this danger is really not very great; after stumbling a few times they would, at last, learn to walk. However, examples of such failures intimidate and generally discourage all further attempts.

Thus it is very difficult for the individual to work himself out of the nonage which has become almost second nature to him. He has even grown to like it, and is at first really incapable of using his own understanding because he has never been permitted to try it. Dogmas and formulas, these mechanical tools designed for reasonable use–or rather abuse–of his natural gifts, are the fetters of an everlasting nonage. The man who casts them off would make an uncertain leap over the narrowest ditch, because he is not used to such free movement. That is why there are only a few men who walk firmly, and who have emerged from nonage by cultivating their own minds.

It is more nearly possible, however, for the public to enlighten itself; indeed, if it is only given freedom, enlightenment is almost inevitable. There will always be a few independent thinkers, even among the self-appointed guardians of the multitude. Once such men have thrown off the yoke of nonage, they will spread about them the spirit of a reasonable appreciation of man’s value and of his duty to think for himself. It is especially to be noted that the public which was earlier brought under the yoke by these men afterwards forces these very guardians to remain in submission, if it is so incited by some of its guardians who are themselves incapable of any enlightenment. That shows how pernicious it is to implant prejudices: they will eventually revenge themselves upon their authors or their authors’ descendants. Therefore, a public can achieve enlightenment only slowly. A revolution may bring about the end of a personal despotism or of avaricious tyrannical oppression, but never a true reform of modes of thought. New prejudices will serve, in place of the old, as guide lines for the unthinking multitude.

This enlightenment requires nothing but freedom–and the most innocent of all that may be called “freedom”: freedom to make public use of one’s reason in all matters. Now I hear the cry from all sides: “Do not argue!” The officer says: “Do not argue–drill!” The tax collector: “Do not argue–pay!” The pastor: “Do not argue–believe!” Only one ruler in the world says: “Argue as much as you please, but obey!” We find restrictions on freedom everywhere. But which restriction is harmful to enlightenment? Which restriction is innocent, and which advances enlightenment? I reply: the public use of one’s reason must be free at all times, and this alone can bring enlightenment to mankind.

On the other hand, the private use of reason may frequently be narrowly restricted without especially hindering the progress of enlightenment. By “public use of one’s reason” I mean that use which a man, as scholar, makes of it before the reading public. I call “private use” that use which a man makes of his reason in a civic post that has been entrusted to him. In some affairs affecting the interest of the community a certain [governmental] mechanism is necessary in which some members of the community remain passive. This creates an artificial unanimity which will serve the fulfillment of public objectives, or at least keep these objectives from being destroyed. Here arguing is not permitted: one must obey. Insofar as a part of this machine considers himself at the same time a member of a universal community–a world society of citizens–(let us say that he thinks of himself as a scholar rationally addressing his public through his writings) he may indeed argue, and the affairs with which he is associated in part as a passive member will not suffer. Thus it would be very unfortunate if an officer on duty and under orders from his superiors should want to criticize the appropriateness or utility of his orders. He must obey. But as a scholar he could not rightfully be prevented from taking notice of the mistakes in the military service and from submitting his views to his public for its judgment. The citizen cannot refuse to pay the taxes levied upon him; indeed, impertinent censure of such taxes could be punished as a scandal that might cause general disobedience. Nevertheless, this man does not violate the duties of a citizen if, as a scholar, he publicly expresses his objections to the impropriety or possible injustice of such levies. A pastor, too, is bound to preach to his congregation in accord with the doctrines of the church which he serves, for he was ordained on that condition. But as a scholar he has full freedom, indeed the obligation, to communicate to his public all his carefully examined and constructive thoughts concerning errors in that doctrine and his proposals concerning improvement of religious dogma and church institutions. This is nothing that could burden his conscience. For what he teaches in pursuance of his office as representative of the church, he represents as something which he is not free to teach as he sees it. He speaks as one who is employed to speak in the name and under the orders of another. He will say: “Our church teaches this or that; these are the proofs which it employs.” Thus he will benefit his congregation as much as possible by presenting doctrines to which he may not subscribe with full conviction. He can commit himself to teach them because it is not completely impossible that they may contain hidden truth. In any event, he has found nothing in the doctrines that contradicts the heart of religion. For if he believed that such contradictions existed he would not be able to administer his office with a clear conscience. He would have to resign it. Therefore the use which a scholar makes of his reason before the congregation that employs him is only a private use, for no matter how sizable, this is only a domestic audience. In view of this he, as preacher, is not free and ought not to be free, since he is carrying out the orders of others. On the other hand, as the scholar who speaks to his own public (the world) through his writings, the minister in the public use of his reason enjoys unlimited freedom to use his own reason and to speak for himself. That the spiritual guardians of the people should themselves be treated as minors is an absurdity which would result in perpetuating absurdities.

But should a society of ministers, say a Church Council, . . . have the right to commit itself by oath to a certain unalterable doctrine, in order to secure perpetual guardianship over all its members and through them over the people? I say that this is quite impossible. Such a contract, concluded to keep all further enlightenment from humanity, is simply null and void even if it should be confirmed by the sovereign power, by parliaments, and the most solemn treaties. An epoch cannot conclude a pact that will commit succeeding ages, prevent them from increasing their significant insights, purging themselves of errors, and generally progressing in enlightenment. That would be a crime against human nature whose proper destiny lies precisely in such progress. Therefore, succeeding ages are fully entitled to repudiate such decisions as unauthorized and outrageous. The touchstone of all those decisions that may be made into law for a people lies in this question: Could a people impose such a law upon itself? Now it might be possible to introduce a certain order for a definite short period of time in expectation of better order. But, while this provisional order continues, each citizen (above all, each pastor acting as a scholar) should be left free to publish his criticisms of the faults of existing institutions. This should continue until public understanding of these matters has gone so far that, by uniting the voices of many (although not necessarily all) scholars, reform proposals could be brought before the sovereign to protect those congregations which had decided according to their best lights upon an altered religious order, without, however, hindering those who want to remain true to the old institutions. But to agree to a perpetual religious constitution which is not publicly questioned by anyone would be, as it were, to annihilate a period of time in the progress of man’s improvement. This must be absolutely forbidden.

A man may postpone his own enlightenment, but only for a limited period of time. And to give up enlightenment altogether, either for oneself or one’s descendants, is to violate and to trample upon the sacred rights of man. What a people may not decide for itself may even less be decided for it by a monarch, for his reputation as a ruler consists precisely in the way in which he unites the will of the whole people within his own. If he only sees to it that all true or supposed [religious] improvement remains in step with the civic order, he can for the rest leave his subjects alone to do what they find necessary for the salvation of their souls. Salvation is none of his business; it is his business to prevent one man from forcibly keeping another from determining and promoting his salvation to the best of his ability. Indeed, it would be prejudicial to his majesty if he meddled in these matters and supervised the writings in which his subjects seek to bring their [religious] views into the open, even when he does this from his own highest insight, because then he exposes himself to the reproach: Caesar non est supra grammaticos. 2    It is worse when he debases his sovereign power so far as to support the spiritual despotism of a few tyrants in his state over the rest of his subjects.

When we ask, Are we now living in an enlightened age? the answer is, No, but we live in an age of enlightenment. As matters now stand it is still far from true that men are already capable of using their own reason in religious matters confidently and correctly without external guidance. Still, we have some obvious indications that the field of working toward the goal [of religious truth] is now opened. What is more, the hindrances against general enlightenment or the emergence from self-imposed nonage are gradually diminishing. In this respect this is the age of the enlightenment and the century of Frederick [the Great].

A prince ought not to deem it beneath his dignity to state that he considers it his duty not to dictate anything to his subjects in religious matters, but to leave them complete freedom. If he repudiates the arrogant word “tolerant”, he is himself enlightened; he deserves to be praised by a grateful world and posterity as that man who was the first to liberate mankind from dependence, at least on the government, and let everybody use his own reason in matters of conscience. Under his reign, honorable pastors, acting as scholars and regardless of the duties of their office, can freely and openly publish their ideas to the world for inspection, although they deviate here and there from accepted doctrine. This is even more true of every person not restrained by any oath of office. This spirit of freedom is spreading beyond the boundaries [of Prussia] even where it has to struggle against the external hindrances established by a government that fails to grasp its true interest. [Frederick’s Prussia] is a shining example that freedom need not cause the least worry concerning public order or the unity of the community. When one does not deliberately attempt to keep men in barbarism, they will gradually work out of that condition by themselves.

I have emphasized the main point of the enlightenment–man’s emergence from his self-imposed nonage–primarily in religious matters, because our rulers have no interest in playing the guardian to their subjects in the arts and sciences. Above all, nonage in religion is not only the most harmful but the most dishonorable. But the disposition of a sovereign ruler who favors freedom in the arts and sciences goes even further: he knows that there is no danger in permitting his subjects to make public use of their reason and to publish their ideas concerning a better constitution, as well as candid criticism of existing basic laws. We already have a striking example [of such freedom], and no monarch can match the one whom we venerate.

But only the man who is himself enlightened, who is not afraid of shadows, and who commands at the same time a well disciplined and numerous army as guarantor of public peace–only he can say what [the sovereign of] a free state cannot dare to say: “Argue as much as you like, and about what you like, but obey!” Thus we observe here as elsewhere in human affairs, in which almost everything is paradoxical, a surprising and unexpected course of events: a large degree of civic freedom appears to be of advantage to the intellectual freedom of the people, yet at the same time it establishes insurmountable barriers. A lesser degree of civic freedom, however, creates room to let that free spirit expand to the limits of its capacity. Nature, then, has carefully cultivated the seed within the hard core–namely the urge for and the vocation of free thought. And this free thought gradually reacts back on the modes of thought of the people, and men become more and more capable of acting in freedom. At last free thought acts even on the fundamentals of government and the state finds it agreeable to treat man, who is now more than a machine, in accord with his dignity


Categorical imperative

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The categorical imperative is the central philosophical concept in the moral philosophy of Immanuel Kant. Introduced in Kant’s 1785 Groundwork for the Metaphysics of Morals, it may be defined as a way of evaluating motivations for action.[citation needed]

According to Kant, human beings occupy a special place in creation, and morality can be summed up in one ultimate commandment of reason, or imperative, from which all duties and obligations derive. He defined an imperative as any proposition that declares a certain action (or inaction) to be necessary.

Hypothetical imperatives apply to someone dependent on them having certain ends:

  • if I wish to quench my thirst, I must drink something;
  • if I wish to acquire knowledge, I must learn.

A categorical imperative, on the other hand, denotes an absolute, unconditional requirement that asserts its authority in all circumstances, both required and justified as an end in itself. It is best known in its first formulation:

Act only according to that maxim whereby you can, at the same time, will that it should become a universal law.[1]

Kant expressed extreme dissatisfaction with the popular moral philosophy of his day, believing that it could never surpass the level of hypothetical imperatives: a utilitarian says that murder is wrong because it does not maximize good for those involved, but this is irrelevant to people who are concerned only with maximizing the positive outcome for themselves. Consequently, Kant argued, hypothetical moral systems cannot persuade moral action or be regarded as bases for moral judgments against others, because the imperatives on which they are based rely too heavily on subjective considerations. He presented a deontological moral system, based on the demands of the categorical imperative, as an alternative.


Nature of the concept

The capacity that underlies deciding what is moral is called pure practical reason, which is contrasted with pure reason (the capacity to know without having been shown) and mere practical reason (which allows us to interact with the world in experience). Hypothetical imperatives tell us which means best achieve our ends. They do not, however, tell us which ends we should choose. The typical dichotomy in choosing ends is between ends that are “right” (e.g., helping someone) and those that are “good” (e.g., enriching oneself). Kant considered the “right” superior to the “good”; to him, the “good” was morally irrelevant. In Kant’s view, a person cannot decide whether conduct is “right,” or moral, through empirical means. Such judgments must be reached a priori, using pure practical reason.[citation needed]

Reason, separate from all empirical experience, can determine the principle according to which all ends can be determined as moral. It is this fundamental principle of moral reason that is known as the categorical imperative. Pure practical reason in the process of determining it dictates what ought to be done without reference to empirical contingent factors. This is the sense in which Kant’s meta-ethical position is objectivist rather than subjectivist.[citation needed] Moral questions are determined independent of reference to the particular subject posing them. It is because morality is determined by pure practical reason rather than particular empirical or sensuous factors that morality is universally valid. This moral universalism has come to be seen as the distinctive aspect of Kant’s moral philosophy and has had wide social impact in the legal and political concepts of human rights and equality.[citation needed]

Freedom and autonomy

Kant viewed the human individual as a rationally self-conscious being with “impure” freedom of choice:

The faculty of desire in accordance with concepts, in-so-far as the ground determining it to action lies within itself and not in its object, is called a faculty to “do or to refrain from doing as one pleases”. Insofar as it is joined with one’s consciousness of the ability to bring about its object by one’s action it is called choice (Willkür); if it is not joined with this consciousness its act is called a wish. The faculty of desire whose inner determining ground, hence even what pleases it, lies within the subject’s reason is called the will (Wille). The will is therefore the faculty of desire considered not so much in relation to action (as choice is) but rather in relation to the ground determining choice in action. The will itself, strictly speaking, has no determining ground; insofar as it can determine choice, it is instead practical reason itself. Insofar as reason can determine the faculty of desire as such, not only choice but also mere wish can be included under the will. That choice which can be determined by pure reason is called free choice. That which can be determined only by inclination (sensible impulse, stimulus) would be animal choice (arbitrium brutum). Human choice, however, is a choice that can indeed be affected but not determined by impulses, and is therefore of itself (apart from an acquired proficiency of reason) not pure but can still be determined to actions by pure will. – Immanuel Kant, Metaphysics of Morals, 6:213-4

For a will to be considered “free”, we must understand it as capable of affecting causal power without being caused to do so. But the idea of lawless free will, that is, a will acting without any causal structure, is incomprehensible. Therefore, a free will must be acting under laws that it gives to itself.

Although Kant conceded that there could be no conceivable example of free will, because any example would only show us a will as it appears to us — as a subject of natural laws — he nevertheless argued against determinism. He proposed that determinism is logically inconsistent: The determinist claims that because A caused B, and B caused C, that A is the true cause of C. Applied to a case of the human will, a determinist would argue that the will does not have causal power and that something outside the will causes the will to act as it does. But this argument merely assumes what it sets out to prove: viz. that the human will is part of the causal chain.

Secondly, Kant remarks that free will is inherently unknowable. Since even a free person could not possibly have knowledge of their own freedom, we cannot use our failure to find a proof for freedom as evidence for a lack of it. The observable world could never contain an example of freedom because it would never show us a will as it appears to itself, but only a will that is subject to natural laws imposed on it. But we do appear to ourselves as free. Therefore he argued for the idea of transcendental freedom — that is, freedom as a presupposition of the question “what ought I to do?” This is what gives us sufficient basis for ascribing moral responsibility: the rational and self-actualizing power of a person, which he calls moral autonomy: “the property the will has of being a law unto itself.”

Good will, duty, and the categorical imperative

Since considerations of the physical details of actions are necessarily bound up with a person’s subjective preferences, and could have been brought about without the action of a rational will, Kant concluded that the expected consequences of an act are themselves morally neutral, and therefore irrelevant to moral deliberation. The only objective basis for moral value would be the rationality of the good will, expressed in recognition of moral duty.

Duty is the necessity to act out of reverence for the moral law set by the categorical imperative. Only a categorical imperative, then, can be the supreme principle of morality.

The First Formulation

Act only according to that maxim whereby you can at the same time will that it should become a universal law without contradiction.

Immanuel Kant, Groundwork of the Metaphysic of Morals[1]

From this step, Kant concludes that a moral proposition that is true must be one that is not tied to any particular conditions, including the identity of the person making the moral deliberation. A moral maxim must imply absolute necessity, which is to say that it must be disconnected from the particular physical details surrounding the proposition, and could be applied to any rational being. This leads to the first formulation of the categorical imperative:

  • “Act only according to that maxim whereby you can at the same time will that it should become a universal law without contradiction.”[1]

Kant divides the duties imposed by this formulation into two subsets:

Perfect duty

According to his reasoning, we first have a perfect duty not to act by maxims that result in logical contradictions when we attempt to universalize them. The moral proposition A: “It is permissible to steal” would result in a contradiction upon universalisation. The notion of stealing presupposes the existence of property, but were A universalized, then there could be no property, and so the proposition has logically negated itself.

In general, perfect duties are those that are blameworthy if not met, as they are a basic required duty for a human being.

Imperfect duty

Second, we have imperfect duties, which are still based on pure reason, but which allow for desires in how they are carried out in practice. Because these depend somewhat on the subjective preferences of humankind, this duty is not as strong as a perfect duty, but it is still morally binding. As such, unlike perfect duties, you do not attract blame should you not complete an imperfect duty but you shall receive praise for it should you complete it, as you have gone beyond the basic duties and taken duty upon yourself. Imperfect duties are circumstantial, meaning simply that you could not reasonably exist in a constant state of performing that duty. This is what truly differentiates between perfect and imperfect duties, because imperfect duties are those duties that are never truly completed. A particular example provided by Kant is the imperfect duty to cultivate one’s own talents.[citation needed]

The Second Formulation

Act in such a way that you treat humanity, whether in your own person or in the person of any other, never merely as a means to an end, but always at the same time as an end.

Immanuel Kant, Groundwork of the Metaphysic of Morals[1]

Every rational action must set before itself not only a principle, but also an end. Most ends are of a subjective kind, because they need only be pursued if they are in line with some particular hypothetical imperative that a person may choose to adopt. For an end to be objective, it would be necessary that we categorically pursue it.

The free will is the source of all rational action. But to treat it as a subjective end is to deny the possibility of freedom in general. Because the autonomous will is the one and only source of moral action, it would contradict the first formulation to claim that a person is merely a means to some other end, rather than always an end in themselves.

On this basis, Kant derives second formulation of the categorical imperative from the first.

By combining this formulation with the first, we learn that a person has perfect duty not to use the humanity of themselves or others merely as a means to some other end. As a slaveowner would be effectively asserting a moral right to own a person as a slave, they would be asserting a property right in another person. But this would violate the categorical imperative because it denies the basis for there to be free rational action at all; it denies the status of a person as an end in themselves. One cannot, on Kant’s account, ever suppose a right to treat another person as a mere means to an end.

The second formulation also leads to the imperfect duty to further the ends of ourselves and others. If any person desires perfection in themselves or others, it would be their moral duty to seek that end for all people equally, so long as that end does not contradict perfect duty.

The Third Formulation

Therefore, every rational being must so act as if he were through his maxim always a legislating member in the universal kingdom of ends.

Immanuel Kant, Groundwork of the Metaphysic of Morals[1]

Because a truly autonomous will would not be subjugated to any interest, it would only be subject to those laws it makes for itself — but it must also regard those laws as if they would be bound to others, or they would not be universalizable, and hence they would not be laws of conduct at all. Thus Kant presents the notion of the hypothetical Kingdom of Ends of which he suggests all people should consider themselves both means and ends.

“Act in such a way that you treat humanity, whether in your own person or in that of another, always at the same time as an end and never merely as a means.”[2] We ought to act only by maxims that would harmonize with a possible kingdom of ends. We have perfect duty not to act by maxims that create incoherent or impossible states of natural affairs when we attempt to universalize them, and we have imperfect duty not to act by maxims that lead to unstable or greatly undesirable states of affairs.

Normative interpretation

Although Kant was intensely critical of the use of examples as moral yardsticks, because they tend to rely on our moral intuitions (feelings) rather than our rational powers, this section will explore some interpretations of the categorical imperative for illustrative purposes.


Kant asserted that lying, or deception of any kind, would be forbidden under any interpretation and in any circumstance. In Groundwork, Kant gives the example of a person who seeks to borrow money without intending to pay it back. This is a contradiction because if it were a universal action, no person would lend money anymore as he knows that he will never be paid back. The maxim of this action, says Kant, results in a contradiction in conceivability (and thus contradicts perfect duty). With lying, it would logically contradict the reliability of language. If it is universally acceptable to lie, then no one would believe anyone and all truths would be assumed to be lies. The right to deceive could also not be claimed because it would deny the status of the person deceived as an end in itself. The theft would be incompatible with a possible kingdom of ends. Therefore, Kant denied the right to lie or deceive for any reason, regardless of context or anticipated consequences.


Kant argued that any action taken against another person to which he or she could not possibly consent is a violation of perfect duty interpreted through the second formulation. If a thief were to steal a book from an unknowing victim, it may have been that the victim would have agreed, had the thief simply asked. However, no person can consent to theft, because the presence of consent would mean that the transfer was not a theft. Because the victim could not have consented to the action, it could not be instituted as a universal law of nature, and theft contradicts perfect duty.


Kant applied his categorical imperative to the issue of suicide in Groundwork for the Metaphysics of Morals,[3] writing that:

A man reduced to despair by a series of misfortunes feels sick of life, but is still so far in possession of his reason that he can ask himself whether taking his own life would not be contrary to his duty to himself. Now he asks whether the maxim of his action could become a universal law of nature. But his maxim is this: from self-love I make as my principle to shorten my life when its continued duration threatens more evil than it promises satisfaction. There only remains the question as to whether this principle of self-love can become a universal law of nature. One sees at once that a contradiction in a system of nature whose law would destroy life by means of the very same feeling that acts so as to stimulate the furtherance of life, and hence there could be no existence as a system of nature. Therefore, such a maxim cannot possibly hold as a universal law of nature and is, consequently, wholly opposed to the supreme principle of all duty.

Immanuel Kant, Groundwork for the Metaphysics of Morals, p30-31


Kant also applies the categorical imperative in Grounding for the Metaphysics of Morals on the subject of “failing to cultivate one’s talents.” He proposes a man who if he cultivated his talents could bring many goods, but he has everything he wants and would prefer to enjoy the pleasures of life instead. The man asks himself how the universality of such a thing works. While Kant agrees that a society could subsist if everyone did nothing, he notes that the man would have no pleasures to enjoy, for if everyone let their talents go to waste, there would be no one to create luxuries that created this theoretical situation in the first place. Not only that, but cultivating one’s talents is a duty to oneself. Thus, it is not willed to make laziness universal, and a rational being has imperfect duty to cultivate its talents. Kant concludes in Grounding:

…he cannot possibly will that this should become a universal law of nature or be implanted in us as such a law by a natural instinct. For as a rational being he necessarily wills that all his faculties should be developed, inasmuch as they are given him for all sorts of possible purposes.[4]


Kant’s last application of the categorical imperative in Grounding for the Metaphysics of Morals is of charity. He proposes a fourth man who finds his own life fine but sees other people struggling with life and who ponders the outcome of doing nothing to help those in need (while not envying them or accepting anything from them). While Kant admits that humanity could subsist (and admits it could possibly perform better) if this were universal, he states in Grounding:

But even though it is possible that a universal law of nature could subsist in accordance with that maxim, still it is impossible to will that such a principle should hold everywhere as a law of nature. For a will that resolved in this way would contradict itself, inasmuch as cases might often arise in which one would have need of the love and sympathy of others and in which he would deprive himself, by such a law of nature springing from his own will, of all hope of the aid he wants for himself.[5]

Cruelty to animals

Kant derived a prohibition against cruelty to animals as a violation of a duty in relation to oneself. According to Kant, man has the imperfect duty to strengthen the feeling of compassion, since this feeling promotes morality in relation to other human beings. But, cruelty to animals deadens the feeling of compassion in man. Therefore, man is obliged not to treat animals brutally (Kant, Metaphysics of Morals, § 17).

Normative criticism

The Golden Rule

The first formulation of the Categorical Imperative appears similar to The Golden Rule.

The ‘Golden Rule’ (in its negative form) says: “Do not impose on others what you do not wish for yourself.”[6]

The ‘Golden Rule’ (in its positive form) says: “Therefore all things whatsoever would that men should do to you, do ye even so to them”.[7]

Kant’s first formulation of CI says: “Act only in accordance with that maxim through which you can at the same time will that it become a universal law.”

Due to this similarity, some have thought the two are identical.[8]

Peter Corning suggests that, “Kant’s objection to the Golden Rule is especially suspect because the categorical imperative (CI) sounds a lot like a paraphrase, or perhaps a close cousin, of the same fundamental idea. In effect, it says that you should act toward others in ways that you would want everyone else to act toward others, yourself included (presumably). Calling it a universal law does not materially improve on the basic concept.”.[9] Corning claims that Ken Bilmore thought so as well.

Kant himself did not think so in Groundwork for the Metaphysics of Morals. Rather, the categorical imperative is an attempt to identify a purely formal and necessarily universally binding rule on all rational agents. The Golden Rule, on the other hand, is neither purely formal nor necessarily universally binding. It is “empirical” in the sense that applying it depends on providing content, like “If you don’t want others to hit you, then don’t hit them.” Also, it is a hypothetical imperative in the sense that it can be formulated, “If you want X done to you, then do X to others.” Kant feared that the hypothetical clause, “if you want X done to you,” remains open to dispute.[10] He wanted an imperative that was categorical: “Do X to others.” And this he thinks he discovered and formulated. Kant thought, therefore, that the Golden Rule (insofar as it is accurate) is derived from the categorical imperative .[11]

Inquiring murderer

One of the first major challenges to Kant’s reasoning came from the French philosopher Benjamin Constant, who asserted that since truth telling must be universal, according to Kant’s theories, one must (if asked) tell a known murderer the location of his prey. This challenge occurred while Kant was still alive, and his response was the essay On a Supposed Right to Tell Lies from Benevolent Motives (sometimes translated On a Supposed Right to Lie because of Philanthropic Concerns). In this reply, Kant agreed with Constant’s inference, that from Kant’s premises one must infer a moral duty not to lie to a murderer.

Kant denied that such an inference indicates any weakness in his premises: not lying to the murderer is required because moral actions do not derive their worth from the expected consequences. He claimed that because lying to the murderer would treat him as a mere means to another end, the lie denies the rationality of another person, and therefore denies the possibility of there being free rational action at all. This lie results in a contradiction in conceivably and therefore the lie is in conflict with duty.

It is possible to conceive of solutions to the problem according to Kantian ethics: one could, for instance, tell the murderer truthfully that they need to protect the person and thus cannot reveal their location. Because such an action might save the potential victim without treating the murderer merely as a means to that end, it seems a more likely candidate as a maxim of action.

Questioning autonomy

Schopenhauer’s criticism of the Kantian philosophy expresses doubt concerning the absence of egoism in the Categorical Imperative. Schopenhauer claimed that the Categorical Imperative is actually hypothetical and egotistical, not categorical. Kierkegaard believed Kantian autonomy was insufficient and that, if unchecked, people tend to be lenient in their own case, either by not exercising the full rigor of the moral law or by not properly disciplining themselves of moral transgressions:

Kant was of the opinion that man is his own law (autonomy) – that is, he binds himself under the law which he himself gives himself. Actually, in a profounder sense, this is how lawlessness or experimentation are established. This is not being rigorously earnest any more than Sancho Panza‘s self-administered blows to his own bottom were vigorous. … Now if a man is never even once willing in his lifetime to act so decisively that [a lawgiver] can get hold of him, well, then it happens, then the man is allowed to live on in self-complacent illusion and make-believe and experimentation, but this also means: utterly without grace.
Papers and Journals

Kant’s categorical imperative and the trial of Adolf Eichmann

In 1961, discussion of Kant’s categorical imperative included even the trial of the infamous SS Lieutenant Colonel Adolf Eichmann in Jerusalem.

As Hannah Arendt wrote in her book on the trial, Eichmann declared “with great emphasis that he had lived his whole life … according to a Kantian definition of duty”. Arendt considered this so “incomprehensible on the face of it” that it confirmed her sense that he wasn’t really thinking at all, just mouthing accepted formulae, thereby establishing his banality.[12] Judge Raveh indeed had asked Eichmann whether he thought he had really lived according to the categorical imperative during the war. Eichmann acknowledged he did not “live entirely according to it, although I would like to do so.” [12]

Deborah Lipstadt, in her book on the trial, takes this as evidence that evil is not banal, but is in fact self-aware.

See also

Immanuel Kant
Perpetual Peace: A Philosophical Sketch



Whether this satirical inscription on a Dutch innkeeper’s sign upon which a burial ground was painted had for its object mankind in general, or the rulers of states in particular, who are insatiable of war, or merely the philosophers who dream this sweet dream, it is not for us to decide. But one condition the author of this essay wishes to lay down. The practical politician assumes the attitude of looking down with great self-satisfaction on the political theorist as a pedant whose empty ideas in no way threaten the security of the state, inasmuch as the state must proceed on empirical principles; so the theorist is allowed to play his game without interference from the worldly-wise statesman. Such being his attitude, the practical politician–and this is the condition I make–should at least act consistently in the case of a conflict and not suspect some danger to the state in the political theorist’s opinions which are ventured and publicly expressed without any ulterior purpose. By this clausula salvatoria the author desires formally and emphatically to deprecate herewith any malevolent interpretation which might be placed on his words.



1. “No Treaty of Peace Shall Be Held Valid in Which There Is Tacitly Reserved Matter for a Future War”

Otherwise a treaty would be only a truce, a suspension of hostilities but not peace, which means the end of all hostilities–so much so that even to attach the word “perpetual” to it is a dubious pleonasm. The causes for making future wars (which are perhaps unknown to the contracting parties) are without exception annihilated by the treaty of peace, even if they should be dug out of dusty documents by acute sleuthing. When one or both parties to a treaty of peace, being too exhausted to continue warring with each other, make a tacit reservation (reservatio mentalis) in regard to old claims to be elaborated only at some more favorable opportunity in the future, the treaty is made in bad faith, and we have an artifice worthy of the casuistry of a Jesuit. Considered by itself, it is beneath the dignity of a sovereign, just as the readiness to indulge in this kind of reasoning is unworthy of the dignity of his minister.

But if, in consequence of enlightened concepts of statecraft, the glory of the state is placed in its continual aggrandizement by whatever means, my conclusion will appear merely academic and pedantic.

2. “No Independent States, Large or Small, Shall Come under the Dominion of Another State by Inheritance, Exchange, Purchase, or Donation”

A state is not, like the ground which it occupies, a piece of property (patrimonium). It is a society of men whom no one else has any right to command or to dispose except the state itself. It is a trunk with its own roots. But to incorporate it into another state, like a graft, is to destroy its existence as a moral person, reducing it to a thing; such incorporation thus contradicts the idea of the original contract without which no right over a people can be conceived.1

Everyone knows to what dangers Europe, the only part of the world where this manner of acquisition is known, has been brought, even down to the most recent times, by the presumption that states could espouse one another; it is in part a new kind of industry for gaining ascendancy by means of family alliances and without expenditure of forces, and in part a way of extending one’s domain. Also the hiring-out of troops by one state to another, so that they can be used against an enemy not common to both, is to be counted under this principle; for in this manner the subjects, as though they were things to be manipulated at pleasure, are used and also used up.

3. “Standing Armies (miles perpetuus) Shall in Time Be Totally Abolished”

For they incessantly menace other states by their readiness to appear at all times prepared for war; they incite them to compete with each other in the number of armed men, and there is no limit to this. For this reason, the cost of peace finally becomes more oppressive than that of a short war, and consequently a standing army is itself a cause of offensive war waged in order to relieve the state of this burden. Add to this that to pay men to kill or to be killed seems to entail using them as mere machines and tools in the hand of another (the state), and this is hardly compatible with the rights of mankind in our own person. But the periodic and voluntary military exercises of citizens who thereby secure themselves and their country against foreign aggression are entirely different.

The accumulation of treasure would have the same effect, for, of the three powers–the power of armies, of alliances, and of money–the third is perhaps the most dependable weapon. Such accumulation of treasure is regarded by other states as a threat of war, and if it were not for the difficulties in learning the amount, it would force the other state to make an early attack.

4. “National Debts Shall Not Be Contracted with a View to the External Friction of States”

This expedient of seeking aid within or without the state is above suspicion when the purpose is domestic economy (e.g., the improvement of roads, new settlements, establishment of stores against unfruitful years, etc.). But as an opposing machine in the antagonism of powers, a credit system which grows beyond sight and which is yet a safe debt for the present requirements–because all the creditors do not require payment at one time–constitutes a dangerous money power. This ingenious invention of a commercial people [England] in this century is dangerous because it is a war treasure which exceeds the treasures of all other states; it cannot be exhausted except by default of taxes (which is inevitable), though it can be long delayed by the stimulus to trade which occurs through the reaction of credit on industry and commerce. This facility in making war, together with the inclination to do so on the part of rulers–an inclination which seems inborn in human nature–is thus a great hindrance to perpetual peace. Therefore, to forbid this credit system must be a preliminary article of perpetual peace all the more because it must eventually entangle many innocent states in the inevitable bankruptcy and openly harm them. They are therefore justified in allying themselves against such a state and its measures.

5. “No State Shall by Force Interfere with the Constitution or Government of Another State”

For what is there to authorize it to do so? The offense, perhaps, which a state gives to the subjects of another state? Rather the example of the evil into which a state has fallen because of its lawlessness should serve as a warning. Moreover, the bad example which one free person affords another as a scandalum acceptum is not an infringement of his rights. But it would be quite different if a state, by internal rebellion, should fall into two parts, each of which pretended to be a separate state making claim to the whole. To lend assistance to one of these cannot be considered an interference in the constitution of the other state (for it is then in a state of anarchy) . But so long as the internal dissension has not come to this critical point, such interference by foreign powers would infringe on the rights of an independent people struggling with its internal disease; hence it would itself be an offense and would render the autonomy of all states insecure.

6. “No State Shall, during War, Permit Such Acts of Hostility Which Would Make Mutual Confidence in the Subsequent Peace Impossible: Such Are the Employment of Assassins (percussores), Poisoners (venefici), Breach of Capitulation, and Incitement to Treason (perduellio) in the Opposing State”

These are dishonorable stratagems. For some confidence in the character of the enemy must remain even in the midst of war, as otherwise no peace could be concluded and the hostilities would degenerate into a war of extermination (bellum internecinum). War, however, is only the sad recourse in the state of nature (where there is no tribunal which could judge with the force of law) by which each state asserts its right by violence and in which neither party can be adjudged unjust (for that would presuppose a juridical decision); in lieu of such a decision, the issue of the conflict (as if given by a so-called “judgment of God”) decides on which side justice lies. But between states no punitive war (bellum punitivum) is conceivable, because there is no relation between them of master and servant.

It follows that a war of extermination, in which the destruction of both parties and of all justice can result, would permit perpetual peace only in the vast burial ground of the human race. Therefore, such a war and the use of all means leading to it must be absolutely forbidden. But that the means cited do inevitably lead to it is clear from the fact that these infernal arts, vile in themselves, when once used would not long be confined to the sphere of war. Take, for instance, the use of spies (uti exploratoribus). In this, one employs the infamy of others (which can never be entirely eradicated) only to encourage its persistence even into the state of peace, to the undoing of the very spirit of peace.

Although the laws stated are objectively, i.e., in so far as they express the intention of rulers, mere prohibitions (leges prohibitivae), some of them are of that strict kind which hold regardless of circumstances (leges strictae) and which demand prompt execution. Such are Nos. 1, 5, and 6. Others, like Nos. 2, 3, and 4, while not exceptions from the rule of law, nevertheless are sub- jectively broader (leges latae) in respect to their observation, containing permission to delay their execution without, however, losing sight of the end. This permission does not authorize, under No. 2, for example, delaying until doomsday (or, as Augustus used to say, ad calendas Graecas) the re-establishment of the freedom of states which have been deprived of it–i.e., it does not permit us to fail to do it, but it allows a delay to prevent precipitation which might injure the goal striven for. For the prohibition concerns only the manner of acquisition which is no longer permitted, but not the possession, which, though not bearing a requisite title of right, has nevertheless been held lawful in all states by the public opinion of the time (the time of the putative acquisition).2.



The state of peace among men living side by side is not the natural state (status naturalis); the natural state is one of war. This does not always mean open hostilities, but at least an unceasing threat of war. A state of peace, therefore, must be established, for in order to be secured against hostility it is not sufficient that hostilities simply be not committed; and, unless this security is pledged to each by his neighbor (a thing that can occur only in a civil state), each may treat his neighbor, from whom he demands this security, as an enemy.3  


 “The Civil Constitution of Every State Should Be Republican”

The only constitution which derives from the idea of the original compact, and on which all juridical legislation of a people must be based, is the republican. 4 This constitution is established, firstly, by principles of the freedom of the members of a society (as men); secondly, by principles of dependence of all upon a single common legislation (as subjects); and, thirdly, by the law of their equality (as citizens). The republican constitution, therefore, is, with respect to law, the one which is the original basis of every form of civil constitution. The only question now is: Is it also the one which can lead to perpetual peace?

The republican constitution, besides the purity of its origin (having sprung from the pure source of the concept of law), also gives a favorable prospect for the desired consequence, i.e., perpetual peace. The reason is this: if the consent of the citizens is required in order to decide that war should be declared (and in this constitution it cannot but be the case), nothing is more natural than that they would be very cautious in commencing such a poor game, decreeing for themselves all the calamities of war. Among the latter would be: having to fight, having to pay the costs of war from their own resources, having painfully to repair the devastation war leaves behind, and, to fill up the measure of evils, load themselves with a heavy national debt that would embitter peace itself and that can never be liquidated on account of constant wars in the future. But, on the other hand, in a constitution which is not republican, and under which the subjects are not citizens, a declaration of war is the easiest thing in the world to decide upon, because war does not require of the ruler, who is the proprietor and not a member of the state, the least sacrifice of the pleasures of his table, the chase, his country houses, his court functions, and the like. He may, therefore, resolve on war as on a pleasure party for the most trivial reasons, and with perfect indifference leave the justification which decency requires to the diplomatic corps who are ever ready to provide it.

In order not to confuse the republican constitution with the democratic (as is commonly done), the following should be noted. The forms of a state (civitas) can be divided either according to the persons who possess the sovereign power or according to the mode of administration exercised over the people by the chief, whoever he may be. The first is properly called the form of sovereignty (forma imperii), and there are only three possible forms of it: autocracy, in which one, aristocracy, in which some associated together, or democracy, in which all those who constitute society, possess sovereign power. They may be characterized, respectively, as the power of a monarch, of the nobility, or of the people. The second division is that by the form of government (forma regiminis) and is based on the way in which the state makes use of its power; this way is based on the constitution, which is the act of the general will through which the many persons become one nation. In this respect government is either republican or despotic. Republicanism is the political principle of the separation of the executive power (the administration) from the legislative; despotism is that of the autonomous execution by the state of laws which it has itself decreed. Thus in a despotism the public will is administered by the ruler as his own will. Of the three forms of the state, that of democracy is, properly speaking, necessarily a despotism, because it establishes an executive power in which “all” decide for or even against one who does not agree; that is, “all,” who are not quite all, decide, and this is a contradiction of the general will with itself and with freedom. 

Every form of government which is not representative is, properly speaking, without form. The legislator can unite in one and the same person his function as legislative and as executor of his will just as little as the universal of the major premise in a syllogism can also be the subsumption of the particular under the universal in the minor. And even though the other two constitutions are always defective to the extent that they do leave room for this mode of administration, it is at least possible for them to assume a mode of government conforming to the spirit of a representative system (as when Frederick II at least said he was merely the first servant of the state).5 On the other hand, the democratic mode of government makes this impossible, since everyone wishes to be master. Therefore, we can say: the smaller the personnel of the government (the smaller the number of rulers), the greater is their representation and the more nearly the constitution approaches to the possibility of republicanism; thus the constitution may be expected by gradual reform finally to raise itself to republicanism. For these reasons it is more difficult for an aristocracy than for a monarchy to achieve the one completely juridical constitution, and it is impossible for a democracy to do so except by violent revolution. 

The mode of governments, 6 however, is incomparably more important to the people than the form of sovereignty, although much depends on the greater or lesser suitability of the latter to the end of [good] government. To conform to the concept of law, however, government must have a representative form, and in this system only a republican mode of government is possible; without it, government is despotic and arbitrary, whatever the constitution may be. None of the ancient so-called “republics” knew this system, and they all finally and inevitably degenerated into despotism under the sovereignty of one, which is the most bearable of all forms of despotism. 


 “The Law of Nations Shall be Founded on a Federation of Free States”

Peoples, as states, like individuals, may be judged to injure one another merely by their coexistence in the state of nature (i.e., while independent of external laws). Each of then, may and should for the sake of its own security demand that the others enter with it into a constitution similar to the civil constitution, for under such a constitution each can be secure in his right. This would be a league of nations, but it would not have to be a state consisting of nations. That would be contradictory, since a state implies the relation of a superior (legislating) to an inferior (obeying), i.e., the people, and many nations in one state would then constitute only one nation. This contradicts the presupposition, for here we have to weigh the rights of nations against each other so far as they are distinct states and not amalgamated into one.

When we see the attachment of savages to their lawless freedom, preferring ceaseless combat to subjection to a lawful constraint which they might establish, and thus preferring senseless freedom to rational freedom, we regard it with deep contempt as barbarity, rudeness, and a brutish degradation of humanity. Accordingly, one would think that civilized people (each united in a state) would hasten all the more to escape, the sooner the better, from such a depraved condition. But, instead, each state places its majesty (for it is absurd to speak of the majesty of the people) in being subject to no external juridical restraint, and the splendor of its sovereign consists in the fact that many thousands stand at his command to sacrifice themselves for something that does not concern them and without his needing to place himself in the least danger.7 The chief difference between European and American savages lies in the fact that many tribes of the latter have been eaten by their enemies, while the former know how to make better use of their conquered enemies than to dine off them; they know better how to use them to increase the number of their subjects and thus the quantity of instruments for even more extensive wars.

When we consider the perverseness of human nature which is nakedly revealed in the uncontrolled relations between nations (this perverseness being veiled in the state of civil law by the constraint exercised by government), we may well be astonished that the word “law” has not yet been banished from war politics as pedantic, and that no state has yet been bold enough to advocate this point of view. Up to the present, Hugo Grotius, Pufendorf, Vattel, and many other irritating comforters have been cited in justification of war, though their code, philosophically or diplomatically formulated, has not and cannot have the least legal force, because states as such do not stand under a common external power. There is no instance on record that a state has ever been moved to desist from its purpose because of arguments backed up by the testimony of such great men. But the homage which each state pays (at least in words) to the concept of law proves that there is slumbering in man an even greater moral disposition to become master of the evil principle in himself (which he cannot disclaim) and to hope for the same from others. Otherwise the word “law” would never be pronounced by states which wish to war upon one another; it would be used only ironically, as a Gallic prince interpreted it when he said, “It is the prerogative which nature has given the stronger that the weaker should obey him.”

States do not plead their cause before a tribunal; war alone is their way of bringing suit. But by war and its favorable issue, in victory, right is not decided, and though by a treaty of peace this particular war is brought to an end, the state of war, of always finding a new pretext to hostilities, is not terminated. Nor can this be declared wrong, considering the fact that in this state each is the judge of his own case. Notwithstanding, the obligation which men in a lawless condition have under the natural law, and which requires them to abandon the state of nature, does not quite apply to states under the law of nations, for as states they already have an internal juridical constitution and have thus outgrown compulsion from others to submit to a more extended lawful constitution according to their ideas of right. This is true in spite of the fact that reason, from its throne of supreme moral legislating authority, absolutely condemns war as a legal recourse and makes a state of peace a direct duty, even though peace cannot be established or secured except by a compact among nations.

For these reasons there must be a league of a particular kind, which can be called a league of peace (foedus pacificum), and which would be distinguished from a treaty of peace (pactum pacis) by the fact that the latter terminates only one war, while the former seeks to make an end of all wars forever. This league does not tend to any dominion over the power of the state but only to the maintenance and security of the freedom of the state itself and of other states in league with it, without there being any need for them to submit to civil laws and their compulsion, as men in a state of nature must submit.

The practicability (objective reality) of this idea of federation, which should gradually spread to all states and thus lead to perpetual peace, can be proved. For if fortune directs that a powerful and enlightened people can make itself a republic, which by its nature must be inclined to perpetual peace, this gives a fulcrum to the federation with other states so that they may adhere to it and thus secure freedom under the idea of the law of nations. By more and more such associations, the federation may be gradually extended.

We may readily conceive that a people should say, “There ought to be no war among us, for we want to make ourselves into a state; that is, we want to establish a supreme legislative, executive, and judiciary power which will reconcile our differences peaceably.” But when this state says, “There ought to be no war between myself and other states, even though I acknowledge no supreme legislative power by which our rights are mutually guaranteed,” it is not at all clear on what I can base my confidence in my own rights unless it is the free federation, the surrogate of the civil social order, which reason necessarily associates with the concept of the law of nations–assuming that something is really meant by the latter.

The concept of a law of nations as a right to make war does not really mean anything, because it is then a law of deciding what is right by unilateral maxims through force and not by universally valid public laws which restrict the freedom of each one. The only conceivable meaning of such a law of nations might be that it serves men right who are so inclined that they should destroy each other and thus find perpetual peace in the vast grave that swallows both the atrocities and their perpetrators. For states in their relation to each other, there cannot be any reasonable way out of the lawless condition which entails only war except that they, like individual men, should give up their savage (lawless) freedom, adjust themselves to the constraints of public law, and thus establish a continuously growing state consisting of various nations (civitas gentium), which will ultimately include all the nations of the world. But under the idea of the law of nations they do not wish this, and reject in practice what is correct in theory. If all is not to be lost, there can be, then, in place of the positive idea of a world republic, only the negative surrogate of an alliance which averts war, endures, spreads, and holds back the stream of those hostile passions which fear the law, though such an alliance is in constant peril of their breaking loose again.8 Furor impius intus . . . fremit horridus ore cruento (Virgil). 


 “The Law of World Citizenship Shall Be Limited to Conditions of Universal Hospitality”

Here, as in the preceding articles, it is not a question of philanthropy but of right. Hospitality means the right of a stranger not to be treated as an enemy when he arrives in the land of another. One may refuse to receive him when this can be done without causing his destruction; but, so long as he peacefully occupies his place, one may not treat him with hostility. It is not the right to be a permanent visitor that one may demand. A special beneficent agreement would be needed in order to give an outsider a right to become a fellow inhabitant for a certain length of time. It is only a right of temporary sojourn, a right to associate, which all men have. They have it by virtue of their common possession of the surface of the earth, where, as a globe, they cannot infinitely disperse and hence must finally tolerate the presence of each other. Originally, no one had more right than another to a particular part of the earth.

Uninhabitable parts of the earth–the sea and the deserts–divide this community of all men, but the ship and the camel (the desert ship) enable them to approach each other across these unruled regions and to establish communication by using the common right to the face of the earth, which belongs to human beings generally. The inhospitality of the inhabitants of coasts (for instance, of the Barbary Coast) in robbing ships in neighboring seas or enslaving stranded travelers, or the inhospitality of the inhabitants of the deserts (for instance, the Bedouin Arabs) who view contact with nomadic tribes as conferring the right to plunder them, is thus opposed to natural law, even though it extends the right of hospitality, i.e., the privilege of foreign arrivals, no further than to conditions of the possibility of seeking to communicate with the prior inhabitants. In this way distant parts of the world can come into peaceable relations with each other, and these are finally publicly established by law. Thus the human race can gradually be brought closer and closer to a constitution establishing world citizenship.

But to this perfection compare the inhospitable actions of the civilized and especially of the commercial states of our part of the world. The injustice which they show to lands and peoples they visit (which is equivalent to conquering them) is carried by them to terrifying lengths. America, the lands inhabited by the Negro, the Spice Islands, the Cape, etc., were at the time of their discovery considered by these civilized intruders as lands without owners, for they counted the inhabitants as nothing. In East India (Hindustan), under the pretense of establishing economic undertakings, they brought in foreign soldiers and used them to oppress the natives, excited widespread wars among the various states, spread famine, rebellion, perfidy, and the whole litany of evils which afflict mankind. 

China 9 and Japan (Nippon), who have had experience with such guests, have wisely refused them entry, the former permitting their approach to their shores but not their entry, while the latter permit this approach to only one European people, the Dutch, but treat them like prisoners, not allowing them any communication with the inhabitants. The worst of this (or, to speak with the moralist, the best) is that all these outrages profit them nothing, since all these commercial ventures stand on the verge of collapse, and the Sugar Islands, that place of the most refined and cruel slavery, produces no real revenue except indirectly, only serving a not very praiseworthy purpose of furnishing sailors for war fleets and thus for the conduct of war in Europe. This service is rendered to powers which make a great show of their piety, and, while they drink injustice like water, they regard themselves as the elect in point of orthodoxy.

Since the narrower or wider community of the peoples of the earth has developed so far that a violation of rights in one place is felt throughout the world, the idea of a law of world citizenship is no high-flown or exaggerated notion. It is a supplement to the unwritten code of the civil and international law, indispensable for the maintenance of the public human rights and hence also of perpetual peace. One cannot flatter oneself into believing one can approach this peace except under the condition outlined here.

Go to the First Supplement, “Of the Guarantee for Perpetual Peace”

Go the the Second Supplement, “Secret Article for Perpetual Peace”

Go to Appendix I, “On the Opposition Between Morality and Politics With Respect to Perpetual Peace”

Go to Appendix II, “Of the Harmony Which the Transcendental Concept of Public Right Established Between Morality and Politics”


1. A hereditary kingdom is not a state which can be inherited by another state, but the right to govern it can be inherited by another physical person. The state thereby acquires a ruler, but he, as a ruler (i.e., as one already possessing another realm), does not acquire the state.

2. It has not without cause hitherto been doubted whether besides the commands (leges praeceptivae) and prohibitions (leges prohibitivae) there could also be permissive laws (leges permissivae) of pure reason. For laws as such contain a principle of objective practical necessity, while permission implies a principle of the practical contingency of certain actions. Hence a law of permission would imply constraint to an action to do that to which no one can be constrained. If the object of the law has the same meaning in both cases, this is a contradiction. But in permissive law, which is in question here, the prohibition refers only to the future mode of acquisition of a right (e.g., by succession), while the permission annuls this prohibition only with reference to the present possession. This possession, though only putative, may be held to be just (possessio putative) in the transition from the state of nature to a civil state, by virtue of a permissive law included under natural law, even though it is [strictly] illegal. But, as soon as it is recognized as illegal in the state of nature, a similar mode of acquisition in the subsequent civil state (after this transition has occurred) is forbidden, and this right to continuing possession would not hold if such a presumptive acquisition had taken place in the civil state. For in this case it would be an infringement which would have to cease as soon as its illegality was discovered.

I have wished only to call the attention of the teachers of natural law to the concept of a lex permissive, which systematic reason affords, particularly since in civil (statute) law use is often made of it. But in the ordinary use of it, there is this difference: prohibitive law stands alone, while permission is not introduced into it as a limiting condition (as it should be) but counted among the exceptions to it. Then it is said, “This or that is forbidden, except Nos. 1, 2, 3,” and so on indefinitely. These exceptions are added to the law only as an afterthought required by our groping around among cases as they arise, and not by any principle. Otherwise the conditions would have had to be introduced into the formula of the prohibition, and in this way it would itself have become a permissive law. It is, therefore, unfortunate that the subtle question proposed by the wise and acute Count von Windischgrätz was never answered and soon consigned to oblivion, because it insisted on the point here discussed. For the possibility of a formula similar to those of mathematics is the only legitimate criterion of a consistent legislation, and without it the so-called ius certum must always remain a pious wish. Otherwise we shall have merely general laws (which apply to a great number of cases), but no universal laws (which apply to all cases) as the concept of law seems to requires.

3. We ordinarily assume that no one may act inimically toward another except when he has been actively injured by the other. This is quite correct if both are under civil law, for, by entering into such a state, they afford each other the requisite security through the sovereign which has power over both. Man (or the people) in the state of nature deprives me of this security and injures me, if he is near me, by this mere status of his, even though he does not injure me actively (facto); he does so by the lawlessness of his condition (statu iniusto) which constantly threatens me. Therefore, I can compel him either to enter with me into a state of civil law or to remove himself from my neighborhood. The postulate which is basic to all the following articles is: All men who can reciprocally influence each other must stand under some civil constitution.

Every juridical constitution which concerns the person who stands under it is one of the following: 

(1) The constitution conforming to the civil law of men in a nation (ius civitatis).

(2) The constitution conforming to the law of nations in their relation to one another (ius gentium).

(3) The constitution conforming to the law of world citizenship, so far as men and states are considered as citizens of a universal state of men, in their external mutual relationships (ius cosmopoliticum).

This division is not arbitrary, being necessary in relation to the idea of perpetual peace. For if only one state were related to another by physical influence and were yet in a state of nature, war would necessarily follow, and our purpose here is precisely to free ourselves of war.

4. Juridical (and hence) external freedom cannot be defined, as is usual, by the privilege of doing anything one wills so long as he does not injure another. For what is a privilege? It is the possibility of an action so far as one does not injure anyone by it. Then the definition would read: Freedom is the possibility of those actions by which one does no one an injury. One does another no injury (he may do as he pleases) only if he does another no injury–an empty tautology. Rather, my external (juridical) freedom is to be defined as follows: It is the privilege to lend obedience to no external laws except those to which I could have given consent. Similarly, external (juridical) equality in a state is that relationship among the citizens in which no one can lawfully bind another without at the same time subjecting himself to the law by which he also can be bound. No definition of juridical dependence is needed, as this already lies in the concept of a state’s constitution as such.

The validity of these inborn rights, which are inalienable and belong necessarily to humanity, is raised to an even higher level by the principle of the juridical relation of man to higher beings, for, if he believes in them, he regards himself by the same principles as a citizen of a supersensuous world. For in what concerns my freedom, I have no obligation with respect to divine law, which can be acknowledged by my reason alone, except in so far as I could have given my consent to it. Indeed, it is only through the law of freedom of my own reason that I frame a concept of the divine will. With regard to the most sublime reason in the world that I can think of, with the exception of God–say, the great Aeon–when I do my duty in my post as he does in his, there is no reason under the law of equality why obedience to duty should fall only to me and the right to command only to him. The reason why this principle of equality does not pertain to our relation to God (as the principle of freedom does) is that this Being is the only one to which the concept of duty does not apply.

But with respect to the right of equality of all citizens as subjects, the question of whether a hereditary nobility may be tolerated turns upon the answer to the question as to whether the pre-eminent rank granted by the state to one citizen over another ought to precede merit or follow it. Now it is obvious that, if rank is associated with birth, it is uncertain whether merit (political skill and integrity) will also follow; hence it would be as if a favorite without any merit were given command. The general will of the people would never agree to this in the original contract, which is the principle of all law, for a nobleman is not necessarily a noble man. With regard to the nobility of office (as we might call the rank of the higher magistracy) which one must earn by merit, this rank does not belong to the person as his property; it belongs to his post, and equality is not thereby infringed, because when a man quits his office he renounces the rank it confers and re-enters into the class of his fellows.

5. The lofty epithets of “the Lord’s anointed…… the executor of the divine will on earth,” and “the vicar of God,” which have been lavished on sovereigns, have been frequently censured as crude and intoxicating flatteries. But this seems to me without good reason. Far from inspiring a monarch with pride, they should rather render him humble, providing he possesses some intelligence (which we must assume). They should make him reflect that he has taken an office too great for man, an office which is the holiest God has ordained on earth, to be the trustee of the rights of men, and that he must always stand in dread of having in some way injured this “apple of God’s eye.”

6. Mallet du Pan, in his pompous but empty and hollow language, pretends to have become convinced, after long experience, of the truth of Pope’s well-known saying:

“For forms of government let fools contest:
Whate’er is best administered, is best.”

If that means that the best-administered state is the state that is best administered, he has, to make use of Swift’s expression, “cracked a nut to come at a maggot.” But if it means that the best-administered state also has the best mode of government, i.e., the best constitution, then it is thoroughly wrong, for examples of good governments prove nothing about the form of government. Whoever reigned better than a Titus and a Marcus Aurelius? Yet one was succeeded by a Domitian and the other by a Commodus. This could never have happened under a good constitution, for their unworthiness for this post was known early enough and also the power of the ruler was sufficient to have excluded them.

7. A Bulgarian prince gave the following answer to the Greek emperor who good-naturedly suggested that they settle their difference by a duel: “A smith who has tongs won’t pluck the glowing iron from the fire with his bare hands.” 

8. It would not ill become a people that has just terminated a war to decree, besides a day of thanksgiving, a day of fasting in order to ask heaven, in the name of the state, for forgiveness for the great iniquity which the human race still goes on to perpetuate in refusing to submit to a lawful constitution in their relation to other peoples, preferring, from pride in their independence, to make use of the barbarous means of war even though they are not able to attain what is sought, namely, the rights of a single state. The thanksgiving for victory won during the war, the hymns which are sung to the God of Hosts (in good Israelitic manner), stand in equally sharp contrast to the moral idea of the Father of Men. For they not only show a sad enough indifference to the way in which nations seek their rights, but in addition express a joy in having annihilated a multitude of men or their happiness.

9.To call this great empire by the name it gives itself, namely “China” and not “Sina” or anything like that, we have only to refer to [A.] Georgi, Alphabetum Tibetanum, pp. 651-54, especially note b. According to the note of Professor [Johann Eberhard] Fischer of Petersburg, there is no definite word used in that country as its name; the most usual word is “Kin,” i.e., gold (which the Tibetans call “Ser”). Accordingly, the emperor is called “the king of gold,” that is, king of the most splendid country in the world. In the empire itself, this word may be pronounced Chin, while because of the ‘guttural sound the Italian missionaries may have called it Kin.–It is clear that what the Romans called the “Land of Seres” was China; the silk, however, was sent to Europe across Greater Tibet (through Lesser Tibet, Bukhara, Persia, and then on).

This suggests many reflections concerning the antiquity of this wonderful state, in comparison with that of Hindustan at the time of its union with Tibet and thence with Japan. We see, on the contrary, that the name “Sina” or “Tshina,” said to have been used by the neighbors of the country, suggests nothing.

Perhaps we can also explain the very ancient but never well-known intercourse of Europe with Tibet by considering the shout, (‘Konx Ompax‘), of the hierophants in the Eleusinian mysteries, as we learn from Hysichius (cf. Travels of the Young Anacharsis, Part V, p. 447 ff.). For, according to Georgi, op. cit., the word Concoia means God, which has a striking resemblance to Konx. Pah-cio (ibid., 520), which the Greeks may well have pronounced pax, means the promulgator legis, divinity pervading the whole of nature (also called Cencresi, p. 177). Om, however, which La Croze translates as benedictus (“blessed”), when applied to divinity perhaps means “the beatified” (p. 507). P. Franz Orazio often asked the Lamas of Tibet what they understood by “God” (Concoia) and always got the answer, “It is the assembly of saints” (i.e., the assembly of the blessed ones who, according to the doctrine of rebirth, finally, after many wanderings through bodies of all kinds, have returned to God, or Burchane; that is to say, they are transmigrated souls, beings to be worshiped, p. 223). That mysterious expression Konx Ompax may well mean “the holy” (Konx), the blessed (Om), the wise (Pax), the supreme being pervading the world (nature personified). Its use in the Greek mysteries may indicate monotheism among the epopts in contrast to the polytheism of the people (though Orazio scented atheism there). How that mysterious word came to the Greeks via Tibet can perhaps be explained in this way; and the early traffic of Europe with China, also through Tibet, and perhaps earlier than communication with Hindustan, is made probable.

For a Polish translation of this essay, see:

Return to Vinnie’s Home Page

Go to the First Supplement, “Of the Guarantee for Perpetual Peace”

Go the the Second Supplement, “Secret Article for Perpetual Peace”

Go to Appendix I, “On the Opposition Between Morality and Politics With Respect to Perpetual Peace”

Go to Appendix II, “Of the Harmony Which the Transcendental Concept of Public Right Established Between Morality and Politics”

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Immanuel Kant
Immanuel Kant (painted portrait).jpg
Born 22 April 1724
Königsberg, Prussia
(now Kaliningrad, Russia)
Died 12 February 1804 (aged 79)
Königsberg, Prussia
Residence Germany
Nationality German
Era 18th-century philosophy
Region Western philosophy
School Kantianism
Enlightenment philosophy
Main interests Epistemology · Metaphysics
Ethics · Logic
Notable ideas Categorical imperative
Transcendental idealism
Synthetic a priori
Noumenon · Sapere aude
Nebular hypothesis
Signature Autograph-ImmanuelKant.png

Immanuel Kant (German: [ɪˈmaːnu̯eːl kant]; 22 April 1724 – 12 February 1804) was a German philosopher. He is the central figure of modern philosophy, and set the terms by which all subsequent thinkers have had to grapple. He argued that human perception structures natural laws, and that reason is the source of morality. His thought continues to hold a major influence in contemporary thought, especially in fields such as metaphysics, epistemology, ethics, political philosophy, and aesthetics.[1]

Kant’s major work, the Critique of Pure Reason (Kritik der reinen Vernunft, 1781),[2] aimed to unite reason with experience to move beyond what he took to be failures of traditional philosophy and metaphysics. He hoped to end an age of speculation where objects outside experience were used to support what he saw as futile theories, while opposing the skepticism of thinkers such as Hume.

He stated:

It always remains a scandal of philosophy and universal human reason that the existence of things outside us … should have to be assumed merely on faith, and that if it occurs to anyone to doubt it, we should be unable to answer him with a satisfactory proof.[3]

Kant proposed a “Copernican Revolution-in-reverse”, saying that:

Up to now it has been assumed that all our cognition must conform to the objects; but … let us once try whether we do not get farther with the problems of metaphysics by assuming that the objects must conform to our cognition.[4]

In simple terms, Kant pointed out that we all shape our experience of things through the filter of our mind. The mind shapes that experience, and among other things, Kant believed the concepts of space and time were programmed into the human brain, as was the notion of cause and effect.[5] We never have direct experience of things, the noumenal world, and what we do experience is the phenomenal world as conveyed by our senses. These observations summarize Kant’s views upon the subject–object problem.

Kant published other important works on ethics, religion, law, aesthetics, astronomy, and history. These included the Critique of Practical Reason (Kritik der praktischen Vernunft, 1788), the Metaphysics of Morals (Die Metaphysik der Sitten, 1797), which dealt with ethics, and the Critique of Judgment (Kritik der Urteilskraft, 1790), which looks at aesthetics and teleology. He aimed to resolve disputes between empirical and rationalist approaches. The former asserted that all knowledge comes through experience; the latter maintained that reason and innate ideas were prior. Kant argued that experience is purely subjective without first being processed by pure reason. He also said that using reason without applying it to experience only leads to theoretical illusions. The free and proper exercise of reason by the individual was a theme both of the Enlightenment, and of Kant’s approaches to the various problems of philosophy.

His ideas influenced many thinkers in Germany during his lifetime. He settled and moved philosophy beyond the debate between the rationalists and empiricists. The philosophers Fichte, Schelling, Hegel and Schopenhauer amended and developed the Kantian system, thus bringing about various forms of German idealism. He is seen as a major figure in the history and development of philosophy. German and European thinking progressed after his time, and his influence still inspires philosophical work today.[6]



Immanuel Kant was born in 1724 in Königsberg, the capital of Prussia at that time, today the city of Kaliningrad in the Russian exclave of Kaliningrad Oblast. He was the fourth of nine children (four of them reached adulthood). Baptized ‘Emanuel’, he changed his name to ‘Immanuel’[7] after learning Hebrew. In his entire life, he never traveled more than ten miles from Königsberg.[8] His father, Johann Georg Kant (1682–1746), was a German harnessmaker from Memel, at the time Prussia’s most northeastern city (now Klaipėda, Lithuania). His mother, Anna Regina Reuter (1697–1737), was born in Nuremberg.[9] Kant’s paternal grandfather had emigrated from Scotland to East Prussia, and his father still spelled their family name “Cant”.[10] In his youth, Kant was a solid, albeit unspectacular, student. He was brought up in a Pietist household that stressed intense religious devotion, personal humility, and a literal interpretation of the Bible. Kant received a stern education – strict, punitive, and disciplinary – that preferred Latin and religious instruction over mathematics and science.[11] Despite being raised in a religious household and still maintaining a belief in God, he was skeptical of religion in later life and was an agnostic.[12][13][14][15][16][17] The common myths concerning Kant’s personal mannerisms are enumerated, explained, and refuted in Goldthwait’s introduction to his translation of Observations on the Feeling of the Beautiful and Sublime.[18] It is often held that Kant lived a very strict and predictable life, leading to the oft-repeated story that neighbors would set their clocks by his daily walks. He never married, but did not seem to lack a rewarding social life – he was a popular teacher and a modestly successful author even before starting on his major philosophical works.

The young scholar

Kant showed a great aptitude to study at an early age. He was first sent to Collegium Fredericianum and then enrolled at the University of Königsberg (where he would spend his entire career) in 1740, at the age of 16.[19] He studied the philosophy of Leibniz and Wolff under Martin Knutzen, a rationalist who was also familiar with developments in British philosophy and science and who introduced Kant to the new mathematical physics of Newton. Knutzen dissuaded Kant from the theory of pre-established harmony, which he regarded as “the pillow for the lazy mind”. He also dissuaded the young scholar from idealism, which was negatively regarded by most philosophers in the 18th century. (The theory of transcendental idealism that Kant developed in the Critique of Pure Reason is not traditional idealism, i.e. the idea that reality is purely mental. In fact, Kant produced arguments against traditional idealism in the second part of the Critique of Pure Reason.) His father’s stroke and subsequent death in 1746 interrupted his studies. Kant became a private tutor in the smaller towns surrounding Königsberg, but continued his scholarly research. 1747 saw the publication of his first philosophical work, Thoughts on the True Estimation of Living Forces.

Early work

Kant is best known for his work in the philosophy of ethics and metaphysics, but he made significant contributions to other disciplines. He made an important astronomical discovery, namely a discovery about the nature of the Earth’s rotation, for which he won the Berlin Academy Prize in 1754.[citation needed]

According to Lord Kelvin:

“Kant pointed out in the middle of last century, what had not previously been discovered by mathematicians or physical astronomers, that the frictional resistance against tidal currents on the earth’s surface must cause a diminution of the earth’s rotational speed. This immense discovery in Natural Philosophy seems to have attracted little attention,–indeed to have passed quite unnoticed, –among mathematicians, and astronomers, and naturalists, until about 1840, when the doctrine of energy began to be taken to heart.”

—Lord Kelvin, physicist, 1897

According to Thomas Huxley:

“The sort of geological speculation to which I am now referring (geological aetiology, in short) was created as a science by that famous philosopher, Immanuel Kant, when, in 1775, he wrote his General Natural History and Theory of the Celestial Bodies; or, an Attempt to Account for the Constitutional and Mechanical Origin of the Universe, upon Newtonian Principles.” —

—Thomas H. Huxley, 1869

In the General History of Nature and Theory of the Heavens (Allgemeine Naturgeschichte und Theorie des Himmels) (1755), Kant laid out the Nebular hypothesis, in which he deduced that the Solar System formed from a large cloud of gas, a nebula. He thus attempted to explain the order of the solar system, seen previously by Newton as being imposed from the beginning by God. Kant also correctly deduced that the Milky Way was a large disk of stars, which he theorized also formed from a (much larger) spinning cloud of gas. He further suggested the possibility that other nebulae might also be similarly large and distant disks of stars. These postulations opened new horizons for astronomy: for the first time extending astronomy beyond the solar system to galactic and extragalactic realms.[20]

From this point on, Kant turned increasingly to philosophical issues, although he continued to write on the sciences throughout his life. In the early 1760s, Kant produced a series of important works in philosophy. The False Subtlety of the Four Syllogistic Figures, a work in logic, was published in 1762. Two more works appeared the following year: Attempt to Introduce the Concept of Negative Magnitudes into Philosophy and The Only Possible Argument in Support of a Demonstration of the Existence of God. In 1764, Kant wrote Observations on the Feeling of the Beautiful and Sublime and then was second to Moses Mendelssohn in a Berlin Academy prize competition with his Inquiry Concerning the Distinctness of the Principles of Natural Theology and Morality (often referred to as “The Prize Essay”). In 1770, at the age of 45, Kant was finally appointed Professor of Logic and Metaphysics at the University of Königsberg. Kant wrote his inaugural dissertation in defence of this appointment. This work saw the emergence of several central themes of his mature work, including the distinction between the faculties of intellectual thought and sensible receptivity. Not to observe this distinction would mean to commit the error of subreption, and, as he says in the last chapter of the dissertation, only in avoidance of this error does metaphysics flourish.

The issue that vexed Kant was central to what twentieth century scholars termed “the philosophy of mind.” The flowering of the natural sciences had led to an understanding of how data reaches the brain. Sunlight may fall upon a distant object, whereupon light is reflected from various parts of the object in a way that maps the surface features (color, texture, etc.) of the object. The light reaches the eye of a human observer, passes through the cornea, is focused by the lens upon the retina where it forms an image similar to that formed by light passing through a pinhole into a camera obscura. The retinal cells next send impulses through the optic nerve and thereafter they form a mapping in the brain of the visual features of the distant object. The interior mapping is not the exterior thing being mapped, and our belief that there is a meaningful relationship between the exterior object and the mapping in the brain depends on a chain of reasoning that is not fully grounded. But the uncertainty aroused by these considerations, the uncertainties raised by optical illusions, misperceptions, delusions, etc., are not the end of the problems.

Kant saw that the mind could not function as an empty container that simply receives data from the outside. Something must be giving order to the incoming data. Images of external objects must be kept in the same sequence in which they were received. This ordering occurs through the mind’s intuition of time. The same considerations apply to the mind’s function of constituting space for ordering mappings of visual and tactile signals arriving via the already described chains of physical causation.

It is often held that Kant was a late developer, that he only became an important philosopher in his mid-50s after rejecting his earlier views. While it is true that Kant wrote his greatest works relatively late in life, there is a tendency to underestimate the value of his earlier works. Recent Kant scholarship has devoted more attention to these “pre-critical” writings and has recognized a degree of continuity with his mature work.[21]

The silent decade

At the age of 46, Kant was an established scholar and an increasingly influential philosopher. Much was expected of him. In correspondence with his ex-student and friend Markus Herz, Kant admitted that, in the Inaugural Dissertation, he had failed to account for the relation and connection between our sensible and intellectual faculties—he needed to explain how we combine sensory knowledge with reasoned knowledge, these being related but very different processes. He also credited David Hume with awakening him from “dogmatic slumber” (circa 1771).[22] Hume had stated that experience consists only of sequences of feelings, images or sounds. Ideas such as ’cause’, goodness, or objects were not evident in experience, so why do we believe in the reality of these? Kant felt that reason could remove this skepticism, and he set himself to solving these problems. He did not publish any work in philosophy for the next eleven years.

Immanuel Kant

Although fond of company and conversation with others, Kant isolated himself. He resisted friends’ attempts to bring him out of his isolation. In 1778, in response to one of these offers by a former pupil, Kant wrote:

“Any change makes me apprehensive, even if it offers the greatest promise of improving my condition, and I am persuaded by this natural instinct of mine that I must take heed if I wish that the threads which the Fates spin so thin and weak in my case to be spun to any length. My great thanks, to my well-wishers and friends, who think so kindly of me as to undertake my welfare, but at the same time a most humble request to protect me in my current condition from any disturbance.”[23]

When Kant emerged from his silence in 1781, the result was the Critique of Pure Reason. Although now uniformly recognized as one of the greatest works in the history of philosophy, this Critique was largely ignored upon its initial publication. The book was long, over 800 pages in the original German edition, and written in a convoluted style. It received few reviews, and these granted no significance to the work. Its density made it, as Johann Gottfried Herder put it in a letter to Johann Georg Hamann, a “tough nut to crack,” obscured by “all this heavy gossamer”.[24] Its reception stood in stark contrast to the praise Kant received for earlier works, such as his Prize Essay and shorter works that preceded the first Critique. These well-received and readable tracts include one on the earthquake in Lisbon that was so popular that it was sold by the page.[25] Prior to the change in course documented in the first Critique, his books sold well, and by the time he published Observations on the Feeling of the Beautiful and Sublime in 1764 he had become a popular author of some note.[26] Kant was disappointed with the first Critique’s reception. Recognizing the need to clarify the original treatise, Kant wrote the Prolegomena to any Future Metaphysics in 1783 as a summary of its main views. He also encouraged his friend, Johann Schultz, to publish a brief commentary on the Critique of Pure Reason.

Kant’s reputation gradually rose through the 1780s, sparked by a series of important works: the 1784 essay, “Answer to the Question: What is Enlightenment?“; 1785’s Groundwork of the Metaphysics of Morals (his first work on moral philosophy); and, from 1786, Metaphysical Foundations of Natural Science. But Kant’s fame ultimately arrived from an unexpected source. In 1786, Karl Reinhold began to publish a series of public letters on the Kantian philosophy. In these letters, Reinhold framed Kant’s philosophy as a response to the central intellectual controversy of the era: the Pantheism Dispute. Friedrich Jacobi had accused the recently deceased G. E. Lessing (a distinguished dramatist and philosophical essayist) of Spinozism. Such a charge, tantamount to atheism, was vigorously denied by Lessing’s friend Moses Mendelssohn, and a bitter public dispute arose among partisans. The controversy gradually escalated into a general debate over the values of the Enlightenment and the value of reason itself. Reinhold maintained in his letters that Kant’s Critique of Pure Reason could settle this dispute by defending the authority and bounds of reason. Reinhold’s letters were widely read and made Kant the most famous philosopher of his era.

Mature work

Kant published a second edition of the Critique of Pure Reason (Kritik der reinen Vernunft) in 1787, heavily revising the first parts of the book. Most of his subsequent work focused on other areas of philosophy. He continued to develop his moral philosophy, notably in 1788’s Critique of Practical Reason (known as the second Critique) and 1797’s Metaphysics of Morals. The 1790 Critique of Judgment (the third Critique) applied the Kantian system to aesthetics and teleology.

In 1792, Kant’s attempt to publish the Second of the four Pieces of Religion within the Bounds of Bare Reason, in the journal Berlinische Monatsschrift, met with opposition from the King’s censorship commission, which had been established that same year in the context of 1789 French Revolution.[27] Kant then arranged to have all four pieces published as a book, routing it through the philosophy department at the University of Jena to avoid the need for theological censorship.[citation needed] Kant got a now famous reprimand from the King,[27] for this action of insubordination. When he nevertheless published a second edition in 1794, the censor was so irate that he arranged for a royal order that required Kant never to publish or even speak publicly about religion.[citation needed] Kant then published his response to the King’s reprimand and explained himself, in the preface of The Conflict of the Faculties.[27]

He also wrote a number of semi-popular essays on history, religion, politics and other topics. These works were well received by Kant’s contemporaries and confirmed his preeminent status in eighteenth century philosophy. There were several journals devoted solely to defending and criticizing the Kantian philosophy. But despite his success, philosophical trends were moving in another direction. Many of Kant’s most important disciples (including Reinhold, Beck and Fichte) transformed the Kantian position into increasingly radical forms of idealism. The progressive stages of revision of Kant’s teachings marked the emergence of German Idealism. Kant opposed these developments and publicly denounced Fichte in an open letter in 1799.[28] It was one of his final acts expounding a stance on philosophical questions. In 1800, a student of Kant, Gottlob Benjamin Jäsche, published a manual of logic for teachers called Logik, which he had prepared at Kant’s request. Jäsche prepared the Logik using a copy of a textbook in logic by Georg Freidrich Meier entitled Auszug aus der Vernunftlehre, in which Kant had written copious notes and annotations. The Logik has been considered of fundamental importance to Kant’s philosophy, and the understanding of it. The great nineteenth century logician Charles Sanders Peirce remarked, in an incomplete review of Thomas Kingsmill Abbott’s English translation of the introduction to the Logik, that “Kant’s whole philosophy turns upon his logic.”[29] Also, Robert Schirokauer Hartman and Wolfgang Schwarz, wrote in the translators’ introduction to their English translation of the Logik, “Its importance lies not only in its significance for the Critique of Pure Reason, the second part of which is a restatement of fundamental tenets of the Logic, but in its position within the whole of Kant’s work.”[30]

Kant’s health, long poor, took a turn for the worse and he died at Königsberg on 12 February 1804, uttering “Es ist gut” (“It is good”) before expiring.[31] His unfinished final work, the fragmentary Opus Postumum, was, as its title suggests, published posthumously.


In Kant’s essay “Answering the Question: What is Enlightenment?“, Kant defined the Enlightenment as an age shaped by the Latin motto Sapere aude (“Dare to Know”). Kant maintained that one ought to think autonomously, free of the dictates of external authority. His work reconciled many of the differences between the rationalist and empiricist traditions of the 18th century. He had a decisive impact on the Romantic and German Idealist philosophies of the 19th century. His work has also been a starting point for many 20th century philosophers.

Kant asserted that, because of the limitations of argumentation in the absence of irrefutable evidence, no one could really know whether there is a God and an afterlife or not. For the sake of morality and as a ground for reason, Kant asserted, people are justified in believing in God, even though they could never know God’s presence empirically. He explained:

All the preparations of reason, therefore, in what may be called pure philosophy, are in reality directed to those three problems only [God, the soul, and freedom]. However, these three elements in themselves still hold independent, proportional, objective weight individually. Moreover, in a collective relational context; namely, to know what ought to be done: if the will is free, if there is a God, and if there is a future world. As this concerns our actions with reference to the highest aims of life, we see that the ultimate intention of nature in her wise provision was really, in the constitution of our reason, directed to moral interests only.[32]

The sense of an enlightened approach and the critical method required that “If one cannot prove that a thing is, he may try to prove that it is not. And if he succeeds in doing neither (as often occurs), he may still ask whether it is in his interest to accept one or the other of the alternatives hypothetically, from the theoretical or the practical point of view. Hence the question no longer is as to whether perpetual peace is a real thing or not a real thing, or as to whether we may not be deceiving ourselves when we adopt the former alternative, but we must act on the supposition of its being real.”[33] The presupposition of God, soul, and freedom was then a practical concern, for “Morality, by itself, constitutes a system, but happiness does not, unless it is distributed in exact proportion to morality. This, however, is possible in an intelligible world only under a wise author and ruler. Reason compels us to admit such a ruler, together with life in such a world, which we must consider as future life, or else all moral laws are to be considered as idle dreams… .”[34]

Kant claimed to have created a “Copernican revolution” in philosophy. This involved two interconnected foundations of his “critical philosophy“:

These teachings placed the active, rational human subject at the center of the cognitive and moral worlds. Kant argued that the rational order of the world as known by science was not just the fortuitous accumulation of sense perceptions.

Conceptual unification and integration is carried out by the mind through concepts or the “categories of the understanding” operating on the perceptual manifold within space and time. The latter are not concepts,[35] but are forms of sensibility that are a priori necessary conditions for any possible experience. Thus the objective order of nature and the causal necessity that operates within it are dependent upon the mind’s processes, the product of the rule-based activity that Kant called, “synthesis. There is much discussion among Kant scholars on the correct interpretation of this train of thought.

The ‘two-world’ interpretation regards Kant’s position as a statement of epistemological limitation, that we are not able to transcend the bounds of our own mind, meaning that we cannot access the “thing-in-itself“. Kant, however, also speaks of the thing in itself or transcendental object as a product of the (human) understanding as it attempts to conceive of objects in abstraction from the conditions of sensibility. Following this line of thought, some interpreters have argued that the thing in itself does not represent a separate ontological domain but simply a way of considering objects by means of the understanding alone – this is known as the two-aspect view.

The notion of the “thing in itself” was much discussed by those who came after Kant. It was argued that since the “thing in itself” was unknowable its existence could not simply be assumed. Rather than arbitrarily switching to an account that was ungrounded in anything supposed to be the “real,” as did the German Idealists, another group arose to ask how our (presumably reliable) accounts of a coherent and rule-abiding universe were actually grounded. This new kind of philosophy became known as Phenomenology, and its founder was Edmund Husserl.

With regard to morality, Kant argued that the source of the good lies not in anything outside the human subject, either in nature or given by God, but rather is only the good will itself. A good will is one that acts from duty in accordance with the universal moral law that the autonomous human being freely gives itself. This law obliges one to treat humanity – understood as rational agency, and represented through oneself as well as others – as an end in itself rather than (merely) as means to other ends the individual might hold. This necessitates practical self-reflection in which we universalize our reasons.

These ideas have largely framed or influenced all subsequent philosophical discussion and analysis. The specifics of Kant’s account generated immediate and lasting controversy. Nevertheless, his theses – that the mind itself necessarily makes a constitutive contribution to its knowledge, that this contribution is transcendental rather than psychological, that philosophy involves self-critical activity, that morality is rooted in human freedom, and that to act autonomously is to act according to rational moral principles – have all had a lasting effect on subsequent philosophy.

Theory of perception

Kant defines his theory of perception in his influential 1781 work The Critique of Pure Reason, which has often been cited as the most significant volume of metaphysics and epistemology in modern philosophy. Kant maintains that our understanding of the external world had its foundations not merely in experience, but in both experience and a priori concepts, thus offering a non-empiricist critique of rationalist philosophy, which is what he and others referred to as his “Copernican revolution“.[36]

Firstly, Kant’s distinction between analytic and synthetic propositions:

  1. Analytic proposition: a proposition whose predicate concept is contained in its subject concept; e.g., “All bachelors are unmarried,” or, “All bodies take up space.”
  2. Synthetic proposition: a proposition whose predicate concept is not contained in its subject concept ; e.g., “All bachelors are happy,” or, “All bodies have weight.”

Analytic propositions are true by nature of the meaning of the words involved in the sentence—we require no further knowledge than a grasp of the language to understand this proposition. On the other hand, synthetic statements are those that tell us something about the world. The truth or falsehood of synthetic statements derives from something outside of their linguistic content. In this instance, weight is not a necessary predicate of the body; until we are told the heaviness of the body we do not know that it has weight. In this case, experience of the body is required before its heaviness becomes clear. Before Kant’s first Critique, empiricists (cf. Hume) and rationalists (cf. Leibniz) assumed that all synthetic statements required experience to be known.

Kant, however, contests this: he claims that elementary mathematics, like arithmetic, is synthetic a priori, in that its statements provide new knowledge, but knowledge that is not derived from experience. This becomes part of his over-all argument for transcendental idealism. That is, he argues that the possibility of experience depends on certain necessary conditions—which he calls a priori forms—and that these conditions structure and hold true of the world of experience. In so doing, his main claims in the “Transcendental Aesthetic” are that mathematic judgments are synthetic a priori and in addition, that Space and Time are not derived from experience but rather are its preconditions.

Once we have grasped the concepts of addition, subtraction or the functions of basic arithmetic, we do not need any empirical experience to know that 100 + 100 = 200, and in this way it would appear that arithmetic is in fact analytic. However, that it is analytic can be disproved thus: if the numbers five and seven in the calculation 5 + 7 = 12 are examined, there is nothing to be found in them by which the number 12 can be inferred. Such it is that “5 + 7” and “the cube root of 1,728” or “12” are not analytic because their reference is the same but their sense is not—that the mathematic judgment “5 + 7 = 12” tells us something new about the world. It is self-evident, and undeniably a priori, but at the same time it is synthetic. And so Kant proves a proposition can be synthetic and known a priori.

Kant asserts that experience is based both upon the perception of external objects and a priori knowledge.[37] The external world, he writes, provides those things that we sense. It is our mind, though, that processes this information about the world and gives it order, allowing us to comprehend it. Our mind supplies the conditions of space and time to experience objects. According to the “transcendental unity of apperception”, the concepts of the mind (Understanding) and the perceptions or intuitions that garner information from phenomena (Sensibility) are synthesized by comprehension. Without the concepts, intuitions are nondescript; without the intuitions, concepts are meaningless—thus the famous statement, “Thoughts without content are empty, intuitions without concepts are blind.”[38]

Kant also makes the claim that an external environment is necessary for the establishment of the self. Although Kant would want to argue that there is no empirical way of observing the self, we can see the logical necessity of the self when we observe that we can have different perceptions of the external environment over time. By uniting all of these general representations into one global representation, we can see how a transcendental self emerges. “I am therefore conscious of the identical self in regard to the manifold of the representations that are given to me in an intuition because I call them all together my representations.”[39]

Categories of the Faculty of Understanding

Kant statue in Belo Horizonte, Brazil

In studying the work of Kant one must realize that there is a distinction between “understanding” as the general concept (in German, das Verstehen) and the “understanding” as a faculty of the human mind (in German, der Verstand, “the intellect”). In much English language scholarship, the word “understanding” is used in both senses.

Kant deemed it obvious that we have some objective knowledge of the world, such as, say, Newtonian physics. But this knowledge relies on synthetic, a priori laws of nature, like causality and substance. The problem, then, is how this is possible. Kant’s solution was to reason that the subject must supply laws that make experience of objects possible, and that these laws are the synthetic, a priori laws of nature that we know apply to all objects before we experience them. So, to deduce all these laws, Kant examined experience in general, dissecting in it what is supplied by the mind from what is supplied by the given intuitions. What has just been explicated is commonly called a transcendental reduction.[40]

To begin with, Kant’s distinction between the a posteriori being contingent and particular knowledge, and the a priori being universal and necessary knowledge, must be kept in mind. For if we merely connect two intuitions together in a perceiving subject, the knowledge is always subjective because it is derived a posteriori, when what is desired is for the knowledge to be objective, that is, for the two intuitions to refer to the object and hold good of it necessarily universally for anyone at anytime, not just the perceiving subject in its current condition. What else is equivalent to objective knowledge besides the a priori, that is to say, universal and necessary knowledge? Nothing else, and hence before knowledge can be objective, it must be incorporated under an a priori category of the understanding.[40][41]

For example, say a subject says, “The sun shines on the stone; the stone grows warm,” which is all he perceives in perception. His judgment is contingent and holds no necessity. But if he says, “The sunshine causes the stone to warm,” he subsumes the perception under the category of causality, which is not found in the perception, and necessarily synthesizes the concept sunshine with the concept heat, producing a necessarily universally true judgment.[40]

To explain the categories in more detail, they are the preconditions of the construction of objects in the mind. Indeed, to even think of the sun and stone presupposes the category of subsistence, that is, substance. For the categories synthesize the random data of the sensory manifold into intelligible objects. This means that the categories are also the most abstract things one can say of any object whatsoever, and hence one can have an a priori cognition of the totality of all objects of experience if one can list all of them. To do so, Kant formulates another transcendental deduction.[40]

Judgments are, for Kant, the preconditions of any thought. Man thinks via judgments, so all possible judgments must be listed and the perceptions connected within them put aside, so as to make it possible to examine the moments when the understanding is engaged in constructing judgments. For the categories are equivalent to these moments, in that they are concepts of intuitions in general, so far as they are determined by these moments universally and necessarily. Thus by listing all the moments, one can deduce from them all of the categories.[40]

One may now ask: How many possible judgments are there? Kant believed that all the possible propositions within Aristotle’s syllogistic logic are equivalent to all possible judgments, and that all the logical operators within the propositions are equivalent to the moments of the understanding within judgments. Thus he listed Aristotle’s system in four groups of three: quantity (universal, particular, singular), quality (affirmative, negative, infinite), relation (categorical, hypothetical, disjunctive) and modality (problematic, assertoric, apodeictic). The parallelism with Kant’s categories is obvious: quantity (unity, plurality, totality), quality (reality, negation, limitation), relation (substance, cause, community) and modality (possibility, existence, necessity).[40]

The fundamental building blocks of experience, i.e. objective knowledge, are now in place. First there is the sensibility, which supplies the mind with intuitions, and then there is the understanding, which produces judgments of these intuitions and can subsume them under categories. These categories lift the intuitions up out of the subject’s current state of consciousness and place them within consciousness in general, producing universally necessary knowledge. For the categories are innate in any rational being, so any intuition thought within a category in one mind is necessarily subsumed and understood identically in any mind. In other words we filter what we see and hear.[40]


Kant ran into a problem with his theory that the mind plays a part in producing objective knowledge. Intuitions and categories are entirely disparate, so how can they interact? Kant’s solution is the schema: a priori principles by which the transcendental imagination connects concepts with intuitions through time. All the principles are temporally bound, for if a concept is purely a priori, as the categories are, then they must apply for all times. Hence there are principles such as substance is that which endures through time, and the cause must always be prior to the effect.[42][43]

Moral philosophy

Immanuel Kant

Kant developed his moral philosophy in three works: Groundwork of the Metaphysic of Morals (1785),[44] Critique of Practical Reason (1788), and Metaphysics of Morals (1797).

In the Groundwork, Kant’s method involves trying to convert our everyday, obvious, rational[45] knowledge of morality into philosophical knowledge. The latter two works followed a method of using “practical reason”, which is based only upon things about which reason can tell us, and not deriving any principles from experience, to reach conclusions which are able to be applied to the world of experience (in the second part of The Metaphysic of Morals).

Kant is known for his theory that there is a single moral obligation, which he called the “Categorical Imperative“, and is derived from the concept of duty. Kant defines the demands of the moral law as “categorical imperatives”. Categorical imperatives are principles that are intrinsically valid; they are good in and of themselves; they must be obeyed in all, and by all, situations and circumstances if our behavior is to observe the moral law. It is from the Categorical Imperative that all other moral obligations are generated, and by which all moral obligations can be tested. Kant also stated that the moral means and ends can be applied to the categorical imperative, that rational beings can pursue certain “ends” using the appropriate “means”. Ends that are based on physical needs or wants always gives merely hypothetical imperatives. The categorical imperative, however, may be based only on something that is an “end in itself”. That is, an end that is a means only to itself and not to some other need, desire, or purpose.[46] He believed that the moral law is a principle of reason itself, and is not based on contingent facts about the world, such as what would make us happy, but to act upon the moral law which has no other motive than “worthiness of being happy”.[47] Accordingly, he believed that moral obligation applies only to rational agents.[48]

A categorical imperative is an unconditional obligation; that is, it has the force of an obligation regardless of our will or desires (Contrast this with hypothetical imperative)[49] In Groundwork of the Metaphysic of Morals (1785) Kant enumerated three formulations of the categorical imperative that he believed to be roughly equivalent.[50]

Kant believed that if an action is not done with the motive of duty, then it is without moral value. He thought that every action should have pure intention behind it; otherwise it was meaningless. He did not necessarily believe that the final result was the most important aspect of an action, but that how the person felt while carrying out the action was the time at which value was set to the result.

In Groundwork of the Metaphysic of Morals, Kant also posited the “counter-utilitarian idea that there is a difference between preferences and values and that considerations of individual rights temper calculations of aggregate utility”, a concept that is an axiom in economics:[51]

Everything has either a price or a dignity. Whatever has a price can be replaced by something else as its equivalent; on the other hand, whatever is above all price, and therefore admits of no equivalent, has a dignity. But that which constitutes the condition under which alone something can be an end in itself does not have mere relative worth, i.e., price, but an intrinsic worth, i.e., a dignity. (p. 53, italics in original).

A phrase quoted by Kant, which is used to summarize the counter-utilitarian nature of his moral philosophy, is Fiat justitia, pereat mundus, (“Let justice be done, though the world perish”), which he translates loosely as “Let justice reign even if all the rascals in the world should perish from it”. This appears in his 1795 Perpetual Peace (Zum ewigen Frieden. Ein philosophischer Entwurf.), Appendix 1.[52][53][54]

The first formulation

The first formulation (Formula of Universal Law) of the moral imperative “requires that the maxims be chosen as though they should hold as universal laws of nature” .[50] This formulation in principle has as its supreme law the creed “Always act according to that maxim whose universality as a law you can at the same time will” and is the “only condition under which a will can never come into conflict with itself [….]”[55]

One interpretation of the first formulation is called the “universalizability test”.[56] An agent’s maxim, according to Kant, is his “subjective principle of human actions”: that is, what the agent believes is his reason to act.[57] The universalisability test has five steps:

  1. Find the agent’s maxim (i.e., an action paired with its motivation). Take for example the declaration “I will lie for personal benefit”. Lying is the action; the motivation is to fulfill some sort of desire. Paired together, they form the maxim.
  2. Imagine a possible world in which everyone in a similar position to the real-world agent followed that maxim. With no exception of one’s self. This is in order for you to hold people to the same principle required of yourself.
  3. Decide whether any contradictions or irrationalities arise in the possible world as a result of following the maxim.
  4. If a contradiction or irrationality arises, acting on that maxim is not allowed in the real world.
  5. If there is no contradiction, then acting on that maxim is permissible, and is sometimes required.

(For a modern parallel, see John Rawls’ hypothetical situation, the original position.)

The second formulation

The second formulation (or Formula of the End in Itself) holds that “the rational being, as by its nature an end and thus as an end in itself, must serve in every maxim as the condition restricting all merely relative and arbitrary ends”.[50] The principle dictates that you “[a]ct with reference to every rational being (whether yourself or another) so that it is an end in itself in your maxim”, meaning that the rational being is “the basis of all maxims of action” and “must be treated never as a mere means but as the supreme limiting condition in the use of all means, i.e., as an end at the same time”.[58]

The third formulation

The third formulation (Formula of Autonomy) is a synthesis of the first two and is the basis for the “complete determination of all maxims”. It says “that all maxims which stem from autonomous legislation ought to harmonize with a possible realm of ends as with a realm of nature”.[50] In principle, “So act as if your maxims should serve at the same time as the universal law (of all rational beings)”, meaning that we should so act that we may think of ourselves as “a member in the universal realm of ends”, legislating universal laws through our maxims (that is, a code of conduct), in a “possible realm of ends”.[59] None may elevate themselves above the universal law, therefore it is one’s duty to follow the maxim(s).

Idea of God

Kant stated the practical necessity for a belief in God in his Critique of Practical Reason. As an idea of pure reason, “we do not have the slightest ground to assume in an absolute manner … the object of this idea”,[60] but adds that the idea of God cannot be separated from the relation of happiness with morality as the “ideal of the supreme good”. The foundation of this connection is an intelligible moral world, and “is necessary from the practical point of view”;[61] compare Voltaire: “If God did not exist, it would be necessary to invent him.”[62] In the Jäsche Logic (1800) he wrote “One cannot provide objective reality for any theoretical idea, or prove it, except for the idea of freedom, because this is the condition of the moral law, whose reality is an axiom. The reality of the idea of God can only be proved by means of this idea, and hence only with a practical purpose, i.e., to act as though (als ob) there is a God, and hence only for this purpose” (9:93, trans. J. Michael Young, Lectures on Logic, p. 590–91).

Along with this ‘idea’ on reason and God, Kant places thought over religion and nature[citation needed], i.e. the idea of religion being natural or naturalistic. Kant saw reason as natural, and as some part of Christianity is based on reason and morality, as Kant points out this is major in the scriptures, it is inevitable that Christianity is ‘natural’. However, it is not ‘naturalistic’ in the sense that the religion does include supernatural or transcendent belief. Aside from this, a key point is that Kant saw that the Bible should be seen as a source of natural morality no matter whether there is/was any truth behind the supernatural factor, meaning that it is not necessary to know whether the supernatural part of Christianity has any truth to abide by and use the core Christian moral code.

Kant articulates in Book Four some of his strongest criticisms of the organization and practices of religious organizations that encourage what he sees as a religion of counterfeit service to God. Among the major targets of his criticism are external ritual, superstition and a hierarchical church order. He sees all of these as efforts to make oneself pleasing to God in ways other than conscientious adherence to the principle of moral rightness in the choice of one’s actions. The severity of Kant’s criticisms on these matters, along with his rejection of the possibility of theoretical proofs for the existence of God and his philosophical re-interpretation of some basic Christian doctrines, have provided the basis for interpretations that see Kant as thoroughly hostile to religion in general and Christianity in particular (e.g., Walsh 1967).Nevertheless, other interpreters consider that Kant was trying to mark off a defensible rational core of Christian belief.[63] Kant sees in Jesus Christ the affirmation of a “pure moral disposition of the heart” that “can make man well-pleasing to God”.[64]

Kant had exposure to Islam as well and reflected about the role of reason therein.[65]

Idea of freedom

In the Critique of Pure Reason,[66] Kant distinguishes between the transcendental idea of freedom, which as a psychological concept is “mainly empirical” and refers to “the question whether we must admit a power of spontaneously beginning a series of successive things or states” as a real ground of necessity in regard to causality,[67] and the practical concept of freedom as the independence of our will from the “coercion” or “necessitation through sensuous impulses”. Kant finds it a source of difficulty that the practical concept of freedom is founded on the transcendental idea of freedom,[68] but for the sake of practical interests uses the practical meaning, taking “no account of… its transcendental meaning,” which he feels was properly “disposed of” in the Third Antinomy, and as an element in the question of the freedom of the will is for philosophy “a real stumbling-block” that has “embarrassed speculative reason”.[67]

Kant calls practical “everything that is possible through freedom”, and the pure practical laws that are never given through sensuous conditions but are held analogously with the universal law of causality are moral laws. Reason can give us only the “pragmatic laws of free action through the senses”, but pure practical laws given by reason a priori[69] dictate “what ought to be done“.[70][71]

The categories of freedom

In the Critique of Practical Reason, at the end of the second Main Part of the Analytics,[72] Kant introduces, in analogy with the categories of understanding their practical counterparts, the categories of freedom. Kant’s categories of freedom appear to have primarily three functions: as conditions of the possibility for actions (i) to be free, (ii) to be comprehensible as free and (iii) to be morally evaluated. For Kant actions, although qua theoretical objects they are always already constituted by means of the theoretical categories, qua practical objects (objects of reason in its practical use, i.e. objects qua possibly good or bad) they are constituted by means of the categories of freedom; and it is only in this way that actions, qua phenomena, can be a consequence of freedom, and can be understood and evaluated as such.[73]

Aesthetic philosophy

Kant discusses the subjective nature of aesthetic qualities and experiences in Observations on the Feeling of the Beautiful and Sublime, (1764). Kant’s contribution to aesthetic theory is developed in the Critique of Judgment (1790) where he investigates the possibility and logical status of “judgments of taste.” In the “Critique of Aesthetic Judgment,” the first major division of the Critique of Judgment, Kant used the term “aesthetic” in a manner that, according to Kant scholar W.H. Walsh, differs from its modern sense.[74] Prior to this, in the Critique of Pure Reason, to note essential differences between judgments of taste, moral judgments, and scientific judgments, Kant abandoned the term “aesthetic” as “designating the critique of taste,” noting that judgments of taste could never be “directed” by “laws a priori“.[75] After A. G. Baumgarten, who wrote Aesthetica (1750–58),[76] Kant was one of the first philosophers to develop and integrate aesthetic theory into a unified and comprehensive philosophical system, utilizing ideas that played an integral role throughout his philosophy.[77]

In the chapter “Analytic of the Beautiful” of the Critique of Judgment, Kant states that beauty is not a property of an artwork or natural phenomenon, but is instead a consciousness of the pleasure that attends the ‘free play’ of the imagination and the understanding. Even though it appears that we are using reason to decide what beautiful, the judgment is not a cognitive judgment,[78] “and is consequently not logical, but aesthetical” (§ 1). A pure judgement of taste is in fact subjective insofar as it refers to the emotional response of the subject and is based upon nothing but esteem for an object itself: it is a disinterested pleasure, and we feel that pure judgements of taste, i.e. judgements of beauty, lay claim to universal validity (§§20–22). It is important to note that this universal validity is not derived from a determinate concept of beauty but from common sense

. Kant also believed that a judgement of taste shares characteristics engaged in a moral judgement: both are disinterested, and we hold them to be universal. In the chapter “Analytic of the Sublime” Kant identifies the sublime as an aesthetic quality that, like beauty, is subjective, but unlike beauty refers to an indeterminate relationship between the faculties of the imagination and of reason, and shares the character of moral judgments in the use of reason. The feeling of the sublime, itself officially divided into two distinct modes (the mathematical and the dynamical sublime), describes two subjective moments, both of which concern the relationship of the faculty of the imagination to reason. Some commentators,[79] however, argue that Kant’s critical philosophy contains a third kind of the sublime, the moral sublime, which is the aesthetic response to the moral law or a representation thereof, and a development of the “noble” sublime in Kant’s theory of 1764. The mathematical sublime is situated in the failure of the imagination to comprehend natural objects that appear boundless and formless, or appear “absolutely great” (§ 23–25). This imaginative failure is then recuperated through the pleasure taken in reason’s assertion of the concept of infinity. In this move the faculty of reason proves itself superior to our fallible sensible self (§§ 25–26). In the dynamical sublime there is the sense of annihilation of the sensible self as the imagination tries to comprehend a vast might. This power of nature threatens us but through the resistance of reason to such sensible annihilation, the subject feels a pleasure and a sense of the human moral vocation. This appreciation of moral feeling through exposure to the sublime helps to develop moral character.

Kant had developed the distinction between an object of art as a material value subject to the conventions of society and the transcendental condition of the judgment of taste as a “refined” value in the propositions of his Idea of A Universal History (1784). In the Fourth and Fifth Theses of that work he identified all art as the “fruits of unsociableness” due to men’s “antagonism in society”,[80] and in the Seventh Thesis asserted that while such material property is indicative of a civilized state, only the ideal of morality and the universalization of refined value through the improvement of the mind of man “belongs to culture”.[81]

Political philosophy

In Perpetual Peace: A Philosophical Sketch[82] Kant listed several conditions that he thought necessary for ending wars and creating a lasting peace. They included a world of constitutional republics.[83] His classical republican theory was extended in the Science of Right’, the first part of the Metaphysics of Morals (1797).[84]

“Kant’s political teaching may be summarized in a phrase: republican government and international organization. In more characteristically Kantian terms, it is doctrine of the state based upon the law (Rechtsstaat) and of eternal peace. Indeed, in each of these formulations, both terms express the same idea: that of legal constitution or of “peace through law.” … Taken simply by itself, Kant’s political philosophy, being essentially a legal doctrine, rejects by definition the opposition between moral education and the play of passions as alternate foundations for social life. The state is defined as the union of men under law. The state rightly so called is constituted by laws which are necessary a priori because they flow from the very concept of law. A regime can be judged by no other criteria nor be assigned any other functions, than those proper to the lawful order as such.” [85]

He opposed “democracy,” which at his time meant direct democracy, believing that majority rule posed a threat to individual liberty. He stated, “…democracy is, properly speaking, necessarily a despotism, because it establishes an executive power in which ‘all’ decide for or even against one who does not agree; that is, ‘all,’ who are not quite all, decide, and this is a contradiction of the general will with itself and with freedom.”[86] As with most writers at the time, he distinguished three forms of government i.e. democracy, aristocracy, and monarchy with mixed government as the most ideal form of it.


Kant lectured on anthropology for over 25 years. His Anthropology from a Pragmatic Point of View was published in 1798. (This was the subject of Michel Foucault‘s doctoral dissertation.) Kant’s Lectures on Anthropology were published for the first time in 1997 in German.[87] The former was translated into English and published by the Cambridge Texts in the History of Philosophy series in 2006.[88]


Kant’s influence on Western thought has been profound.[89] Over and above his influence on specific thinkers, Kant changed the framework within which philosophical inquiry has been carried out. He accomplished a paradigm shift: very little philosophy is now carried out as an extension, or in the style of pre-Kantian philosophy. This shift consists in several closely related innovations that have become axiomatic, in philosophy itself and in the social sciences and humanities generally:

  • Kant’s “Copernican revolution”, that placed the role of the human subject or knower at the center of inquiry into our knowledge, such that it is impossible to philosophize about things as they are independently of us or of how they are for us;[90]
  • His invention of critical philosophy, that is of the notion of being able to discover and systematically explore possible inherent limits to our ability to know through philosophical reasoning
  • His creation of the concept of “conditions of possibility”, as in his notion of “the conditions of possible experience” – that is that things, knowledge, and forms of consciousness rest on prior conditions that make them possible, so that, to understand or to know them, we must first understand these conditions
  • His theory that objective experience is actively constituted or constructed by the functioning of the human mind
  • His notion of moral autonomy as central to humanity
  • His assertion of the principle that human beings should be treated as ends rather than as means

Some or all of these Kantian ideas can be seen in schools of thought as different from one another as German Idealism, Marxism, positivism, phenomenology, existentialism, critical theory, linguistic philosophy, structuralism, post-structuralism, and deconstructionism.[91][dubious ]

Historical influence

Statue of Immanuel Kant in Kaliningrad (Königsberg), Russia

During his own life, there was much critical attention paid to his thought. He did have a positive influence on Reinhold, Fichte, Schelling, Hegel, and Novalis during the 1780s and 1790s. The school of thinking known as German Idealism developed from his writings. The German Idealists Fichte and Schelling, for example, tried to bring traditional “metaphysically” laden notions like “the Absolute,” “God,” or “Being” into the scope of Kant’s critical thought.[92] In so doing, the German Idealists tried to reverse Kant’s view that we cannot know what we cannot observe.

Hegel was one of his first major critics. In response to what he saw as Kant’s abstract and formal account, Hegel brought about an ethic focused on the “ethical life” of the community.[93] But Hegel’s notion of “ethical life” is meant to subsume, rather than replace, Kantian ethics. And Hegel can be seen as trying to defend Kant’s idea of freedom as going beyond finite “desires,” by means of reason. Thus, in contrast to later critics like Nietzsche or Russell, Hegel shares some of Kant’s most basic concerns.[94]

Kant’s thinking on religion was used in Britain to challenge the decline in religious faith in the nineteenth century. British Catholic writers, notably G. K. Chesterton and Hilaire Belloc, followed this approach. Ronald Englefield debated this movement, and Kant’s use of language. See Ronald Englefield‘s article,[95] reprinted in Englefield[96] Criticisms of Kant were common in the realist views of the new positivism at that time.

Arthur Schopenhauer was strongly influenced by Kant’s transcendental idealism. He, like G. E. Schulze, Jacobi and Fichte before him, was critical of Kant’s theory of the thing in itself. Things in themselves, they argued, are neither the cause of what we observe nor are they completely beyond our access. Ever since the first Critique of Pure Reason philosophers have been critical of Kant’s theory of the thing in itself. Many have argued, if such a thing exists beyond experience then one cannot posit that it affects us causally, since that would entail stretching the category ‘causality’ beyond the realm of experience. For a review of this problem and the relevant literature see The Thing in Itself and the Problem of Affection in the revised edition of Henry Allison’s Kant’s Transcendental Idealism. For Schopenhauer things in themselves do not exist outside the non-rational will. The world, as Schopenhauer would have it, is the striving and largely unconscious will.

With the success and wide influence of Hegel’s writings, Kant’s influence began to wane, though there was in Germany a movement that hailed a return to Kant in the 1860s, beginning with the publication of Kant und die Epigonen in 1865 by Otto Liebmann. His motto was “Back to Kant”, and a re-examination of his ideas began (See Neo-Kantianism). During the turn of the 20th century there was an important revival of Kant’s theoretical philosophy, known as the Marburg School, represented in the work of Hermann Cohen, Paul Natorp, Ernst Cassirer,[97] and anti-Neo-Kantian Nicolai Hartmann.[98]

Kant’s notion of “Critique” or criticism has been quite influential. The Early German Romantics, especially Friedrich Schlegel in his “Athenaeum Fragments”, used Kant’s self-reflexive conception of criticism in their Romantic theory of poetry.[99] Also in Aesthetics, Clement Greenberg, in his classic essay “Modernist Painting”, uses Kantian criticism, what Greenberg refers to as “immanent criticism”, to justify the aims of Abstract painting, a movement Greenberg saw as aware of the key limitiaton—flatness—that makes up the medium of painting.[100] French philosopher Michel Foucault was also greatly influenced by Kant’s notion of “Critique” and wrote several pieces on Kant for a re-thinking of the Enlightenment as a form of “critical thought”. He went so far as to classify his own philosophy as a “critical history of modernity, rooted in Kant”.[101]

Kant believed that mathematical truths were forms of synthetic a priori knowledge, which means they are necessary and universal, yet known through intuition.[102] Kant’s often brief remarks about mathematics influenced the mathematical school known as intuitionism, a movement in philosophy of mathematics opposed to Hilbert’s formalism, and the logicism of Frege and Bertrand Russell.[103]

Influence on modern thinkers

West German postage stamp, 1974, commemorating the 250th anniversary of Kant’s birth.

With his Perpetual Peace, Kant is considered to have foreshadowed many of the ideas that have come to form the democratic peace theory, one of the main controversies in political science.[104]

The Kantian paradigm shift in philosophy and metaphysics has been sustained. Some British and American philosophers trace their intellectual origins to Hume:[105] however, Kant acknowledged Hume as awakening him from his ‘dogmatic slumbers’, and his work articulated and clarified the issues looked at by Hume.[106] (See The silent decade section, above).

Prominent recent Kantians include the British philosopher P. F. Strawson,[107] the American philosophers Wilfrid Sellars[108] and Christine Korsgaard.[109]

Due to the influence of Strawson and Sellars, among others, there has been a renewed interest in Kant’s view of the mind. Central to many debates in philosophy of psychology and cognitive science is Kant’s conception of the unity of consciousness.[110]

Kant’s work on mathematics and synthetic a priori knowledge is also cited by theoretical physicist Albert Einstein as an early influence on his intellectual development.[111]

Jürgen Habermas and John Rawls are two significant political and moral philosophers whose work is strongly influenced by Kant’s moral philosophy.[112] They have each argued against relativism,[113] supporting the Kantian view that universality is essential to any viable moral philosophy.

Kant’s influence also has extended to the social and behavioral sciences, as in the sociology of Max Weber, the psychology of Jean Piaget, and the linguistics of Noam Chomsky. Because of the thoroughness of the Kantian paradigm shift, his influence extends to thinkers who neither specifically refer to his work nor use his terminology.

Scholars have shown that Kant’s critical ethos has also inspired nonwestern political thinkers, including the Muslim political reformer Tariq Ramadan.[114]

Tomb and statue

Immanuel Kant’s tomb today

Kant’s tomb is today in a mausoleum adjoining the northeast corner of Königsberg Cathedral in what is now known as Kaliningrad, Russia. The mausoleum was constructed by the architect Friedrich Lahrs and was finished in 1924 in time for the bicentenary of Kant’s birth. Originally, Kant was buried inside the cathedral, but in 1880 his remains were moved outside and placed in a neo-Gothic chapel adjoining the northeast corner of the cathedral. Over the years, the chapel became dilapidated before it was demolished to make way for the mausoleum, which was built on the same spot, where it is today.

The tomb and its mausoleum are some of the few artifacts of German times preserved by the Soviets after they conquered and annexed the city. Today, many newlyweds bring flowers to the mausoleum.

Artifacts previously owned by Kant, known as Kantiana, were included in the Königsberg City Museum. However, the museum was destroyed during World War II.

A replica of the statue of Kant that stood in German times in front of the main University of Königsberg building was donated by a German entity in the early 1990s and placed in the same grounds.

After the expulsion of Königsberg’s German population at the end of World War II, the historical University of Königsberg where Kant taught was replaced by the Russian-speaking Kaliningrad State University, which took up the campus and surviving buildings of the historic German university. In 2005, that Russian-speaking university was renamed Immanuel Kant State University of Russia in honour of Kant. The change of name was announced at a ceremony attended by President Vladimir Putin of Russia and Chancellor Gerhard Schröder of Germany, and the university further formed a Kant Society, dedicated to the study of Kantianism.

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