Classic Works

Immanuel Kant, Perpetual Peace: A Philosophic Sketch (1795)

Kant and the Birth of Modern Idealism

The classic source of modern idealism in international relations theory is Immanuel Kant’s 1795 essay “Perpetual Peace: A Philosophic Sketch.” There, the German philosopher (1724-1804) takes up the question of whether perpetual peace is the preserve of men in their graves. Answering in the negative, Kant delineates the conditions necessary for the establishment of perpetual peace among nations, argues that statesmen are morally obligated to seek those conditions, and assures us that those conditions will eventually obtain. He envisions the world slowly progressing toward a federation of independent republics at peace with one another.

In important ways, Kant’s “Perpetual Peace” constitutes a fundamental break with the tradition of modern realism begun by Machiavelli and Hobbes. Most important is Kant’s insistence that morality must guide foreign policy. Yet Kant does not return to pre-modern idealism. On the contrary, he follows and even radicalizes Hobbes’s characterization of the status quo as a state of nature. Insofar as his advocacy of a worldwide federation of states is animated by an aversion to this condition, one can say that Kant’s idealistic position emerges dialectically out of Hobbes’s realistic position. Indeed, Kant follows a path that emerges out of Hobbes’s thought, namely, escaping the state of nature among nations by means of a social contract. Furthermore, Kant’s prediction that perpetual peace can and will be realized is only a more intense expression of the hopefulness for human progress that marks modern thought from the beginning. Kant’s emphasis on the good that philosophers, if permitted to express themselves freely in public, can do betrays far greater confidence in the good of enlightenment than the pre-modern idealists ever had.

Preliminary Articles of a Perpetual Peace

Kant lays out six articles of perpetual peace, which together constitute the First Section of the essay. He proceeds, in the Second Section, to identify three definitive articles of perpetual peace. These articles are followed by a series of supplements and appendices. The distinction Kant draws between preliminary and definitive articles of perpetual peace makes clear from the outset that he regards the achievement of perpetual peace as a long, gradual process. As their name suggests, the preliminary articles are necessary but insufficient first steps toward that goal.

As Kant explains in his more systematic account of international relations in The Metaphysics of Morals, states, in their external relations with one another, exist in “a state of nature…hence in a condition of constant war” (53). Because there is no common legal authority to which it might appeal in this condition, a state, if it “believes that it has been injured by another state,” “is entitled to resort to violence” (56). Kant insists that even though no state can do injustice to another in this condition given that it is “devoid of right,” the condition is “in the highest degree unjust in itself.” Neighboring states are therefore “bound to abandon such a condition” in favor of “a federation of peoples in accordance with the idea of an original social contract, so that states will protect one another against external aggression while refraining from interference in one another’s internal disagreements” (54). The six preliminary articles of perpetual peace aim at producing the conditions under which such a federation can be formed. Adhering to them is the first thing that states must do in fulfilling the duty to abandon the state of nature.

The six preliminary articles are as follows.

  1. No conclusion of peace shall be considered valid as such if it was made with a secret reservation of the material for a future war.
  2. No independently existing state, whether it be large or small, may be acquired by another state by inheritance, exchange, purchase or gift.
  3. Standing armies will gradually be abolished altogether.
  4. No national debt shall be contracted in connection with the external affairs of the state.
  5. No state shall forcibly interfere in the constitution and government of another state.
  6. No state at war with another shall permit such acts of hostility as would make mutual confidence impossible during a future time of peace. Such acts would include the employment of assassins or poisoners, breach of agreements, the instigation of treason within the enemy state.

The first article seems to be a mere point of semantics. Since peace is by definition perpetual, whenever any party to an agreement ending hostilities makes a secret reservation of material for a future war, peace has not really been concluded. But this article actually gets at the heart of Kantian morality. As Kant explains in the second appendix to “Perpetual Peace,” “the transcendental formula of public right” consists in the proposition that “[a]ll actions affecting the rights of other human beings are wrong if their maxim is not compatible with their being made public” (126). This criterion of publicity derives from the more fundamental criterion of universality. As Kant writes in the Groundwork of the Metaphysic of Morals, the fundamental moral duty, or the categorical imperative, is to “[a]ct as if the maxim of your action were to become through your will a universal law of nature” (89). To make a secret reservation of the material for a future war in concluding a peace treaty would be to violate this duty. The secrecy of the action indicates that the actor could not will that all other states act similarly. The imperative of publicity and, more fundamentally, of universality shows that the Kantian statesmen cannot be concerned exclusively with the particular interest of his country. His pursuit of national interest must be regulated by the categorical imperative. The remaining articles are further examples of this.

Articles 2-5 are all aimed at obviating or mitigating the causes of war. Kant’s explanation of the second article, like the first, has a somewhat academic character. States are societies of men and, by definition, are not possessions to be transferred among princes. The practical significance of this point, however, is that the proprietary view that rulers take of their states causes conflict and, what is more, runs afoul of the rights of their subjects, who, in the characteristic formula of Kantian morality, ought to be regarded not as mere means but as ends in themselves (94).

The prohibition on standing armies contemplated by Article 3 similarly aims not only at diminishing the likelihood of war but also at protecting “the rights of man in one’s own person” (95). With respect to the former, Kant views the accumulation of relative power of any kind, whether military, financial, or diplomatic, as an incitement to one’s neighbors. In the state of nature, it amounts to a threat that triggers “the right of anticipatory attack” (56). With respect to protecting the rights of man, Kant distinguishes citizens’ voluntarily undergoing periodic military training to secure themselves and their country from “the hiring of men to kill or to be killed,” which he likens to using men “as mere machines and instruments” (95). A “citizen,” he explains, “must always be regarded as a co-legislative member of the state (i.e., not just as a means, but also an end in himself), and he must therefore give his free consent through his representatives not only to the waging of war in general, but also to ever particular declaration of war” (55).

The fourth article is intended to combat a modern innovation, the credit system, that Kant worries will do away with one of the age-old limits on warfare, scarce resources. The fifth article’s prohibition on forcible interference in the domestic politics of another state precludes a whole category of warfare, one that, as we shall see, we might not expect Kant to rule out. The internal lawlessness of a state, Kant reasons, does not amount to an injury to other states. Those other states therefore have no justification for interfering. Here we see the concept of autonomy, so central to Kant’s understanding of the moral relations of human beings, applied to states.

While Kant accepts that wars will go on for some time, he insists, in the final preliminary article, that war be conducted in such a way that it does not make future peace impossible. The premise of this article is that, if peace is ever to be concluded between warring states, there must be some modicum of trust between those states even when they are at war with one another. For, should a peace treaty be concluded between states that do not trust one another to keep their word, that treaty will be a dead letter. Without mutual trust, each state will be secretly preparing for a resumption of hostilities. According to the first preliminary article, such an agreement does not even count as a genuine peace treaty. The bleak outcome of this dynamic, Kant warns, is “a war of extermination,” which would eliminate the possibility of perpetual peace (96). Kant claims that “diabolical arts” such as “the employment of assassins…or poisoners, breach of agreements, the instigation of treason…within the enemy state” and even “the employment of spies” “inevitably lead to such a war” and are therefore prohibited (96-97). They all destroy the conditions of trust among warring states and therewith the preconditions for perpetual peace.

Kant’s explanation of the sixth preliminary article surprisingly contains a statement on punitive war. He argues that the very concept of punitive warfare is incoherent on the grounds that “war is only a regrettable expedient for asserting one’s rights by force within a state of nature, where no court of justice is available to judge with legal authority” (96). In the absence of such a court, “neither party can be declared an unjust enemy, for this would presuppose a judge’s decision; only the outcome of the conflict, as in the case of a so-called ‘judgment of God’, can decide who is right” (96). While Kant does not make clear why he includes this critique of retributive war in his explanation of Article 6, the reason would seem to be that retributive war, like spying and the other diabolical arts, eliminates the possibility of mutual trust among warring states and gives rise to wars of extermination. Thus Kant indicates that not only immoralism in warfare but also moralism in warfare stands in the way of perpetual peace. In this respect, we find Kant in the camp of Hobbes and the modern realists over and against Thomas Aquinas and the Christian just war tradition. Kant’s idealism is modern and not medieval insofar as it rules out the only form of warfare that the medieval idealists approved of. This distinction sheds light on Kant’s understanding of the place of morality in international relations. He agrees with Hobbes that the state of war is amoral, but insists that there is a moral obligation to escape this state. War, for Kant, can be just in the sense that it is so limited as to hasten this escape but not in the sense that it entails the just prosecution of a wrongdoer.

In some ways Kant’s preliminary articles of peace reflect a moderate acceptance of the limits to achieving perpetual peace in the short term. These articles do not outlaw war, they merely regulate it. The designation “preliminary” indicates that adherence to these articles is merely a first step toward that goal. What is more, Kant allows states “subjective latitude” in following Articles 2-4. There are circumstances, he admits, in which following these articles would hinder rather than promote the goal. But he is at pains to make clear that this allowance does not entail any compromise on the goal. “[A]ny delay,” he explains, “is permitted only as a means of avoiding a premature implementation which might frustrate the whole purpose of the article” (97). No end other than the establishment of perpetual peace can justify deviation from these articles.

Given this, one can only regard Kant’s position as entailing a radical reorientation of the ends of foreign policy. It is a reorientation from national ends to cosmopolitan ends. More fundamentally, it is, as Kant makes clear in the first appendix, a moral reorientation, from expediency to duty. Kant emphatically breaks with the Hobbesian outlook underlying modern realism, in which morality is conceived as “a general doctrine of expediency, i.e. a theory of the maxims by which one might select the most useful means of furthering one’s own advantage” (116). This is no morality at all, according to Kant. For the core of morality is duty, the fulfillment of which involves subordinating one’s own good to principle. Contra Hobbes, Kant insists that “all politics must bend the knee before right” (125). Kant takes particular exception to the “realistic” view that man cannot do what he ought to do, for example, the “man will never want to do what is necessary in order to attain the goal of eternal peace” (117). Our knowledge of human nature is too limited, in Kant’s view, to make such a prediction. We do not have sufficient grounds for abandoning the hope for perpetual peace or, in turn, the dutiful pursuit of perpetual peace. The “realistic” view must be combated not only because it is false but also because it is a self-fulfilling prophecy. If people are convinced that perpetual peace is impossible, then it will not come about.

Kant holds out as exemplary the “moral politician, i.e., someone who conceives of the principles of political expediency in such a way that they can co-exist with morality” while condemning the “political moralist, i.e. one who fashions his morality to suit his own advantage as a statesman” (118). The former makes it his “duty” to assure that “any faults which could not have been prevented…in the political constitution or in the relations between states…are corrected as soon as possible…even if selfish interests have to be sacrificed” (118). As in his description of the preliminary articles, Kant here concedes that the moral politician need not correct these faults immediately. Indeed, he ought not to do so unless or until it is certain that the can actually succeed in correcting them. For instance, a revolution may ultimately be required in order to correct the constitution of a state, but it ought not to be undertaken until the state is prepared for such a correction.

Definitive Articles of a Perpetual Peace

In his three definitive articles of a perpetual peace, Kant lays out the necessary and sufficient conditions for the achievement of perpetual peace. The guiding premise is that “that state of peace must be formally instituted, for a suspension of hostilities is not in itself a guarantee of peace” (98). In this respect, Kant is simply applying Hobbes’s argument to international relations. Unlike Hobbes, Kant thinks that it is necessary and possible formally to institute a state of peace among nations just as it is among men. He affirms that, in a state of nature, that is, in the absence of a common authority, the mere existence of a state permanently threatens every other state such that any of those others may take “hostile action” against it even though that state may not have “actively injured” them (98). The only way out of this dynamic is the establishment of “some kind of civil constitution,” in the case of international relations, “a constitution based on the international right of states in their relationships with one another (ius gentium)” (98). The “founding of such a union in the most comprehensive form possible” becomes, in Kant’s theory, “the rightful basis of all political prudence” (129). As we shall see, the character of this union, the extent to which it resembles a state, is not entirely clear. Kant’s concern to establish peace is counterbalanced by his concern to preserve the freedom of states and of their inhabitants.

Perpetual peace depends not only upon establishing an international civil constitution, which Kant takes up in the second definitive article, but also upon establishing republican civil constitutions within each state. This is the subject of the first definitive article, in which Kant articulates what has come to be called “democratic peace theory.” According to Kant “A republican constitution is founded upon three principles: firstly, the principle of freedom for all members of society (as men); secondly, the principle of the dependence of everyone upon a single common legislation (as subjects); and thirdly, the principle of legal equality for everyone (as citizens)” (99). This, in Kant’s view, is the only legitimate constitution. The establishment of such constitutions in the nations of the world also happens to serve the goal of perpetual peace. For, under a republican constitution, popular consent is required for a state to go to war and that consent is unlikely to be forthcoming given the various sacrifices the people would be required to make in waging war. A major cause of war over history, in Kant’s view, is that states’ going to war has generally been determined by princes for whom war does not entail much in the way of sacrifice.

This has been an extremely influential argument. But it almost always travels under the misleading heading “democratic peace theory,” despite the distinction Kant draws between republicanism and democracy. According to Kant, states can be classified in terms of “the different persons who exercise supreme authority”—one (autocracy), several (aristocracy), or all (democracy)—or in terms of “the way in which the nation is governed by its ruler, whoever that may be”—separated legislature and executive (republic), or united legislature and executive (despotism) (100-101). The separation of legislative and executive powers requires a representative form of government, in Kant’s view. And, in democracies, the people are ruled by themselves rather than by representatives. Autocracies and aristocracies, while imperfect, are more likely to partake of “the spirit of a representative system” and have the potential to become republican “by gradual reforms” whereas democracies can only become republican “by means of a violent revolution” (101). Democratic despotism is, in Kant’s eyes, the worst form of government. This is what “the so-called ‘republics’ of antiquity” really were (102). Of course, these so-called republics of antiquity tended toward bellicosity. Their example shows that popular consent alone does not necessarily lessen the likelihood of war and may even augment it. The character of the people and their representatives in republics, perhaps especially modern republics in which private and commercial life is elevated, must be more pacific than that of the ancient assemblies.

Kant envisions republics, impelled by their natural inclination “to seek perpetual peace,” to form a federation of states “securing the freedom of each state in accordance with the idea of international right” (104). Yet states need not passively wait for their neighbors to join such a federation of their own accord. On the contrary, “[e]ach nation, for the sake of its own security, can and ought to demand of the others that they should enter along with it into a constitution, similar to a civil one, within which the rights of each could be secured” (102). This, again, is the logic of Hobbes’s state of nature. The primary obstacle to the establishment of such an international federalism, Kant suggests, is the pride that makes states, or their rulers, cling to their independence. To combat this, Kant, appealing to their pride or shame, compares them to the savages who “cling to their lawless freedom…the freedom of folly to the freedom of reason” (103).

Another obstacle that Kant must overcome is the widespread impression that the prevailing state of affairs among nations is not so dreadful, that it is not entirely bereft of justice but rather ordered according to the traditional ius gentium or right of nations. Kant disparages theorists of the right of nations, singling out Grotius, Pufendorf, and Vattel in particular, as “sorry comforters” whose writings are appealed to whenever they can be used to justify war but never are effective in keeping states from going to war (103). These theorists fail to understand that the establishment of right among nations requires the establishment of some common authority with the capacity to constrain states to conform to right (103). For all his lamenting of the status quo, Kant does see in the appeals to right made by states, however disingenuous, a sign that “man possesses a greater moral capacity, still dormant at present, to overcome eventually the evil principle within him…and to hope that others will do likewise” (103). Here, we see a sign of the progressive hope animating “Perpetual Peace.”

Kant’s extension of Hobbes’s argument to international relations would seem to culminate in the establishment of a sovereign world state and an annihilation of all existing states (or all but one). Yet Kant explicitly distinguishes his call for a federation of states from a call for a sovereign world state. States, insofar as “they already have a lawful internal constitution,” Kant reasons, have a certain dignity that individuals in the state of nature lack. They “have outgrown the coercive right of others to subject them to a wider legal constitution in accordance with their conception of right” (104). Hence it would be unjust to compel states to give up their independent existence. The only just way for states to fulfill the duty to pursue peace is to form a federation aimed, unlike a mere “peace treaty,” at ending “all wars for good” and guaranteeing the freedom of each of its members (104). Yet Kant goes on to suggest that states voluntarily subsuming themselves under one world state is the “only…rational way in which states coexisting with other states can emerge from the lawless condition of pure warfare” (105). But states will not voluntarily do this, perhaps because they are too proud. “[A]n enduring and gradually expanding federation likely to prevent war” is the best available alternative (105). It is suboptimal because it cannot guarantee that “the current of man’s inclination to defy the law and antagonize his fellows” will never burst “forth anew” (105). One can add that there are a host of practical questions about how a federation of states will effectively enforce the law that Kant insists is essential for perpetual peace.

In the final definitive article of a perpetual peace, Kant argues that states must treat foreigners hospitably, that is, not treat them “with hostility, so long as [they behave] in a peaceable manner” (106). This right to hospitality stems, according to Kant, from man’s “right to communal possession of the earth’s surface” (106). By nature, no man has any superior claim to any part of the earth. Over history, of course, the earth has been divided into states. While Kant does not question the legitimacy of national divisions, he does insist that individuals retain the right to travel and establish themselves around the world as long as they do so peacefully. Kant indicates that this article aims to promote the cosmopolitanism needed for perpetual peace. “In this way,” he writes, “continents distant from each other can enter into peaceful mutual relations which may eventually be regulated by public laws, thus bringing the human race nearer and nearer to a cosmopolitan constitution” (106).

In seeking to foster this cosmopolitan spirit, Kant opposes the imperialist policies of eighteenth-century Europe. Claiming territory around the world as though it were uninhabited, Europeans fail to fulfill the duty of peaceful travel that corresponds to the right of hospitality. In identifying commerce as the cause of Europe’s imperial exploits, Kant indicates a limit to Montesquieu’s hopeful predictions of the pacific effects of international trade. Kant sees no good in this imperialism. Not only is it unjust, it is also unprofitable and, given European pretensions to piety, hypocritical (107).

On the Guarantee of a Perpetual Peace

Kant’s progressivism, which distinguishes him from previous theorists of international relations, comes to sight most vividly in the first supplement to “Perpetual Peace,” titled “On the Guarantee of a Perpetual Peace” (108). There he assures us that “Perpetual peace is guaranteed by no less an authority than the great artist Nature herself” (108). (Kant speculates that divine providence may guarantee perpetual peace, but refrains from speaking of it here on the grounds that such speculation is outside the “bounds of possible experience,” i.e., the realm of reason.) It turns out that our natural, amoral or even immoral inclinations lead us toward perpetual peace in spite of ourselves. Nature, Kant explains, has “taken care that human beings are able to live in all the areas where they are settled…driven them in all directions by means of war, so that they inhabit even the most inhospitable regions…[a]nd…compelled them by the same means to enter into more or less legal relationships” (109-10).

Kant argues that human beings have a deeply ingrained natural inclination to bellicosity connected to their love of honor (111-12). While this would seem to undermine any hope of establishing perpetual peace, it actually sets off a dynamic that ends in the realization of precisely this hope. Scattered across the globe, in large part as a result of war, “each people would find itself confronted by another neighbouring people pressing upon it, thus forcing it to form itself internally into a state in order to encounter the other as an armed power” (112). The formation of a state does not presuppose moral goodness on the part of the citizens; it is sufficient to construct institutions that channel their naturally selfish inclinations in such a way that “compel one another to submit to coercive laws, thereby producing a condition of peace within which the laws can be enforced” (113). Submission by all to law is an essential dimension of republicanism, which, as previously noted, serves the cause of perpetual peace. The establishment of such “a good political constitution” is what makes it possible for the people “to attain a good level of moral culture” (113).

Nature also promotes the realization of international right by maintaining “the separate existence of many independent adjoining states” (113). It does this by means of linguistic and religious differences, which keep the nations from intermingling. Kant acknowledges that these differences can cause war, but he claims that they prevent a greater evil, namely, “an amalgamation of separate nations under a single power which has overruled the rest and created a universal monarchy” (113). Such a world state would necessarily be “a soulless despotism,” which would, in turn, “lapse into anarchy” (113). Here we see Kant’s concern for freedom qualifying his argument for world government. Kant suggests that the enduring division of the world into separate nations is not as inimical to peace as it might seem. He blithely predicts that, “as culture grows and men gradually move towards greater agreement over their principles,” the linguistic and religious difference separating nations “lead to mutual understanding and peace” (114). He also assures us that “peace is created and guaranteed by an equilibrium of forces and a most vigorous rivalry” (114). In other words, a balance of power can serve the cause of peace.

Even as nature separates states in these ways, it unifies them by way of their natural inclination for material gain. “[T]he spirit of commerce,” Kant claims, “sooner or later takes hold of every people, and it cannot exist side by side with war” (114). Recognizing that commerce and the gain that comes from it depends upon peace, states are driven by non-moral motives to prevent the outbreak of war. Despite his awareness of the dangers of commercial imperialism, Kant here echoes Montesquieu in identifying the pacifying effects of commerce.

Kant’s aim here and throughout the essay is to show that there are grounds for expecting that the goal perpetual peace, the object of our moral duty, will be achieved, that it is “more than an empty chimera” (114). He is concerned to provide encouragement to those who might doubt the practicability of this goal and might, for that reason, be discouraged from fulfilling their duty. Yet the argument that the achievement of perpetual peace is inevitable, even providentially ordained, raises questions about whether it is necessary for moral men to pursue that goal. This, finally, is the paradox of “Perpetual Peace.” This paradox presents in sharp relief the two poles of Kant’s idealism: his subordination of expediency to duty in the conduct of foreign policy and his expectation that right will ultimately prevail among nations.



Recommended Translations of Kant’s Major Political Works:

Kant, Immanuel. Groundwork of the Metaphysic of Morals. Translated by H. J. Paton. New York: Harper

Perennial Modern Thought, 2009.

———. Political Writings. Translated by H. B. Nisbet. Edited by Hans Reiss. Cambridge:

Cambridge University Press, 1991.

Selected Secondary Works on Kant:

Boucher, David. “International and Cosmopolitan Societies: Locke, Vattel, and Kant.” Chap. 11 in Political Theories of International Relations. Oxford: Oxford University Press, 1998.

Doyle, Michael. “Kant, Liberal Legacies, and Foreign Affairs.” Philosophy and Public Affairs 12 (Part 1, Summer 1983; Part 2, Fall 1983): 205-35, 323-53.

Friedrich, Carl J. Inevitable Peace. Cambridge, MA: Harvard University Press, 1948.

Gallie, W. B. “Kant on Perpetual Peace.” Chap. 2 in Philosophers of Peace and War: Kant, Clausewitz, Marx, Engels, and Tolstoy. Cambridge: Cambridge University Press, 1979.

Hassner, Pierre. “Les concepts de guerre et de paix chez Kant.” Revue française de science politique 11, no. 3 (September 1961): 642-70.

Hurrell, Andrew. “Kant and the Kantian Paradigm in International Relations.” Review of International Studies 16, no. 3 (1990): 183-204.

Pangle, Thomas L., and Peter J. Ahrensdorf. “Modern Idealism.” Chap. 6 in Justice among Nations: On the Moral Basis of Power and Peace. Lawrence: University Press of Kansas, 1999.

Shell, Susan Meld. “Kant on Just War and ‘Unjust Enemies’: Reflections on a ‘Pleonasm’.” Kantian Review 10 (January 2005): 82-111.

Thompson, Janna. “Achieving Perpetual Peace: Kant’s Universal History.” Chap. 2 in Justice and World Order: A Philosophical Inquiry. London: Routledge, 1992.

Tuck, Richard. “Rousseau and Kant.” Chap. 6 in The Rights of War and Peace: Political Thought and the International Order from Grotius to Kant. Oxford: Oxford University Press, 1999.

Waltz, Kenneth. “Kant, Liberalism, and War.” American Political Science Review 56, no. 2 (June 1962): 331-40.