Perhaps more than any other philosopher, Immanuel Kant has suffered the praise of having been labeled an historical optimist. Kant’s writings on international affairs have been misconstrued as a defense of the both the desirability and inevitability of a world federation of democracies bound by law. This rendering of Kant has been aided by a selective attention to a few key works and a cultivated ignorance of his more pessimistic remarks on the human condition elsewhere. The truth is that Kant’s theory of international affairs is complicated, eluding clean classification as “realist” or “liberal,” but altogether gloomier than is commonly thought. Although the optimist may dream of perpetual peace, no such harmony can be hewn from “the crooked timber of humanity.” Kant’s view of history is in fact quite pessimistic, and his prescriptions for politics are in many ways consistent with the realist paradigm. Mankind faces a Sisyphean task: an unending struggle between the universal and particular, harmony and multiplicity, sympathy and antagonism.

The case for Kant-as-liberal-optimist is straightforward: in Perpetual Peace and the Doctrine of Right, he speaks of the condition of injustice in which states find themselves, arranged in an international anarchy with no higher authority. Like the state of nature among individuals, states are subjected to the unilateral whims of their potential adversaries, a condition formally incompatible with the duty to respect each as an end-in-itself. Just as men must overcome this anarchic condition of injustice by establishing a civil state, states must institute an international legal order in the form of a federation of states submitting to a common adjudicative authority.  Only then can coercion become regulated in the international sphere and represent the omnilateral will of the human race, just as the state represents the will of its people.

If only states were to submit to this regime, war might be done away with. This, however, is possible only in a federation of republics, since they alone will be constituted in a way to abolish the motive for war. Here is the origin of the “democratic peace” doctrine Kant purportedly advanced: for any state with a democratic constitution, “the consent of the citizens . . . is required to determine . . . ‘Whether there shall be war or not?’ Hence, nothing is more natural than that they should be very loth to enter upon so undesirable an undertaking, for . . . they would necessarily be resolving to bring upon themselves all the horrors of War.” Only a democratic world order, in which each state’s population internalizes the costs of its own behavior, can organize itself into a liberal world order in which states are regulated by law.

And yet Kant is elsewhere less sanguine about the prospects for peace. He claims in the Doctrine of Right that “perpetual peace, the ultimate goal of the whole right of nations, is indeed an unachievable idea”—“idea,” as we will soon see, being the operative word. He even characterizes the history of the human race as afflicted by an unavoidable antagonism which cannot—and indeed should not—be cured. Is Kant simply an incoherent thinker, at times a hopeful liberal, elsewhere a pessimist?

We must first understand Kant’s conception of humanity as participating in two worlds, the sensuous and intelligible. Man is at once rational and free, therefore subject to laws of reason and accountable for his actions, and also prone to sensual inclinations, therefore liable to disobey his rational duties when given over to temptation. To say that man ought to act in some way is not to say that he will, but only that, from the practical point of view of free choice, he can and should. A purely rational being, a Holy Will, devoid of sensuous content, could only ever affirm the laws of reason. Animals, on the other hand, obey their instincts and are incapable of freedom and, for this reason, morality also. Man alone is capable of both recognizing the moral law and choosing to disobey it, and it is for this reason that Kant claims that people are by nature evil.

Whether by weakness of will, impurity of motive, or the radical evil of freely choosing immorality, man lives in a fallen condition, inflicting himself on humanity with a cruelty unseen even in beasts. As evidence, Kant offers “international affairs where civilized nations stand vis-à-vis one another in a relationship of a raw state of nature (a continuing state of war), and are firmly resolved never to depart from that . . . This is so much the case that the philosophical chiliasm, who hoped for a state of perpetual peace based on a federation of nations as a world republic, was ridiculed as mentally raptured.” Concupiscence, the inclination toward sin that rests at the base of man’s soul, is incurable, playing itself out time and again in the bloody annals of history. Kant’s judgment is fatalistic, for “as long as a state has another adjacent state which it might hope to subdue, it strives to enlarge itself through the subjugation of this other, and therefore also to make itself a universal monarchy . . . But this monster . . . after having swallowed all neighboring states, finally dissolves of itself and separates through uproar and discord into many smaller states which, instead of striving toward a union of states (a republic of free, allied peoples), simply and of itself starts the process all over again in order never to cease the war.”

What are we to make of Kant’s simultaneous enjoinder to establish liberal order and his pessimism about its prospects? At times it seems as though Kant’s views, especially in Perpetual Peace and the Doctrine of Right, entertain the genuine possibility of perpetual peace through democratization. But this is mistaken, resting on a misunderstanding of Kant’s notion of republican government, a condition that is, like perpetual peace, an unachievable idea. Where the Kantian optimists have failed is to conflate the regulative and the constitutive.

In his Critique of Pure Reason, Kant distinguishes between the regulative and constitutive use of ideas. The latter, he claims, is the mistake of all systems of dogmatic metaphysics—to take the principles of reason as actually constituting objects of the world of appearances apart from one’s own judgment. Space and time are constitutive categories, but ideas are not—phenomena are ordered according to these categories, and every object given in intuition conforms to them a priori. Regulative ideas, by contrast, are merely principles of judgment that, although not formative elements of the world of appearances, must nonetheless be presupposed to render man’s activities coherent. The unity of nature is one such regulative principle—we cannot know as a matter of sense certainty that all sensible particulars are integrated in a lawful whole, but such a unity must be assumed in order to make scientific inquiry possible.

There are practical regulative ideas as well, the presupposition of which is necessary for action, but which are not to be thought constitutive of reality. The existences of God and of an immortal soul are such ideas that must be assumed in order to regulate our actions, but for which we have no theoretical proof. When Kant speaks of an idea, he is speaking in this sense: a formal principle exceeding all bounds of experience, that is not an empirical law governing the world of things, but is instead a necessary postulate to guide our activities. The idea is not an object of possible knowledge, but a necessary assumption that renders knowledge (or, in this case, action) coherent.

So what of the idea of perpetual peace and the prospects of a liberal-democratic world order? Kant writes:

Now morally practical reason pronounces in us its irresistible veto: there is to be no war . . . So the question is no longer whether perpetual peace is something real or a fiction, and whether we are not deceiving ourselves in our theoretical judgment when we assume that it is real. Instead, we must act as if it is something real, though perhaps it is not; we must work toward establishing perpetual peace and the kind of constitution that seems to us most conducive to it . . . And even if the complete realization of this objective always remains a pious wish, still we are certainly not deceiving ourselves in adopting the maxim of working incessantly towards it.

Perpetual peace, as Kant earlier stated, is nothing more than an idea, an end which, like the “greatest good” or “absolute knowledge,” can never be achieved, but that serves as the constant object of our activity. The moral law demands that we strive for the establishment of justice in the relation among civil states through the creation of a liberal world order. But, as Kant writes, there are empirical causes that disrupt this task—the competition of states, the ebbing and flowing of empires, the spirit of acquisitiveness, and so on. Try as the spirit may, the body will subvert it, and so the idea in its purity can never become an actuality, just as the form of a universal concept is always corrupted by the particularity of its material instance.