Alexander Moseley's Philosophy of War Pages


Immanuel Kant

Picture of Kant by one of my pupils (Alexandra O, aged 9)

Immanuel Kant on War

Dr Alexander Moseley




            In terms of influence in Western philosophy, Kant (1724-1804) ranks amongst the greatest, and recently his ethical framework of the categorical imperative and duty has been exploited in the field of international political theory.

            He was born in Koenisberg, Prussia (now Kaliningrad, Russia). After studying religion and the classics at school, Kant attended the University of Koenisberg to study physics and mathematics. After a few years of tutoring to wealthy families, Kant, on earning his doctorate, he took up a fee-paying lectureship. Eventually the university gave him a chair in logic and metaphysics.

            The sections explored here are from Kant’s Metaphysics of Morals, and from Perpetual Peace.


            The general thrust of Kant’s thoughts on international affairs are best described by his ethical stance on universalism. The world is made up of rational beings who possess duties towards one another, hence Kant is not interested in the balance of power politics of political realism, but of the overriding cosmopolitan nature of human life. The ethical life for Kant is duty-based—‘deontological’. In contradiction to the consequentialists, who argue that moral judgments are made on the results of actions, Kant insists that it is the intention of the agent that ought to be judged; his ethics is thus ‘agent-centred’ rather than ‘result centred’. But duties do not emanate from one’s own preferences or feeling, nor do they emanate from one’s locality, one’s culture or nation for example. Such laws may be unreasonable, that is they might not be universal in application, and universalisibility is the key to how moral an action is. The categorical imperative invokes firstly the principle of universalisation, and secondly that persons should never be treated as means to another’s ends, but always as ends in themselves.The resulting code of morality has therefore nothing to do with empirical phenomena, it is to be thoroughly a-priori in nature: the agent should ask him or herself, “could I will that everybody in the world would follow this principle under relevantly similar conditions”, and as Donaldson points out, there are marked similiarties between Rawls’s ‘veil of ignorance’ and Kant’s rationalist deontology. [1]

            Kant’s agent centred universalism leads him to propound the need for a free society, whose government legislates on a-priori grounds, regardless of empirical ends. Kant’s international political theory stands in opposition to contractarian theories, whose essential tenets entail that morality and justice can only emerge once the social contract has been implemented—this is especially true of the Hobbesian analysis of the international state of nature: without an overriding world Leviathan or cooperating governments justice and morality cannot exist; whereas for Kant it is morality that justifies cooperation. [2] Kant’s system also opposes that of cultural relativism, for its morality, if it exists at all, is particularist—i.e., it emanates from the locality rather than from universal conditions.

            The categorical imperative and apriori considerations lead Kant to formulate his international political philosophy. Three key elements appear: the state is to be viewed as a moral person; the earth is deemed to be originally owned by all; and perpetual peace ought to be the goal for humanity. [3]


            The thesis that states are to be considered as moral persons presents grave implications for individual rights within the state, but Kant no doubt uses it to resolve the Hobbesian view of the international state of nature as a state of war. If states are moral persons, it follows that they ought to treat one another as ends in themselves and not as means, as the analogous categorical imperative applies to individuals. It is a useful logical solution for his system, yet it can imply that states should be viewed as inviolable entities rather than as instruments of the governed. However, Kant acknowledges that a government shuold procure the safety of  its civilians and their property, but that it does not follow that a government owns the civilians, for people should be considered to be colegislators of the state, and should not be treated as means to others’ ends. They must give their free assent if they are to be armed to fight.

            Since they are moral persons, states have the right to go to war to defend their existence. Governments have rights to peace—which include the right to be neutral, the guarantee of peace and the right to form alliances for mutual defence; but above all, moral reasoning demands that there be no war (p.160, § 160). Indeed the demand for universal peace is the final end of Kant’s doctrine of the Right -it is what reason dictates should be the proper condition of humanity, and hence all other acts should defer to it. Therefore, war is the gravest injustice and should be avoided. It follows for Kant, that in the absence of a world government, all governments have a duty to leave it to form a federal league of nations. This message constitutes the thrust of Perpetual Peace and it the founding hallmark of twentieth century attempts to remove the threat of world war, firstly in the institution of the League of Nations (1919-39) and then in the more effective United Nations (1949-).

            Similar to acts of injustice at the individual level, the Kantian just war begins with a wrong committed, or with the attempt to prevent such an act. Kant extends his concept of just war beyond self-defense and anticipated self-defence to also inclue “the menacing increase in another state’s power (by its acquisition of territory).” (§56) Against such an arms race, the just government has the right to retaliate.

However, despite the justice of fighting a war against an aggressor or potential aggressor, Kant maintains that a government in the international state of nature does not have the right to punish, for that right can only come from a legitimate authority, and since there is no such legitimate authority, so state can punish another. Historically, the West has attempted to create such a body in the Hague conventions (1899, 1907, 1954) and the Geneva Conventions (1864, 1949, 1977) with the backing of the United Nations. [4]

            The unjust war is defined as any action by a government, which, if universalised, would make impossible peace among the nations of the world. Kant includes the violation of treaties; but in effect a nation cannot be unjust in what is essentially a condition of injustice. “A just enemy would be one that I would be doing wrong by resisting; but then he would also not be my enemy.” (§ 60, p.156)

            Until there exists a world federation, properly speaking all rights are provisional. The world federation should be the goal of mankind, yet Kant does not believe that it is an achievable goal, given the difficult nature of governing great distances. Accordingly, humanity should aim to create federations -voluntary associations of member states abiding by a common constitution.

            Moving on to his thoughts on jus in bello, it is interesting that Kant finds the concept almost contradictory, but maintains that it should involve the right to leave the international state of nature and to form the rightful condition of a federation. A war should not aim to exterminate the enemy or to subjugate it, since all nations have a right to preserve themselves—but not by acquiring other states, for such imperialism could be used to threaten others again.

            The actual warfare a just government may use may extend to anything except that which would make its subjects “unfit to be citizens”. (§57) Such acts involve the use of spies, using assassins, poisoners, and snipers, or using disseminators of false propaganda -in general, any means used that could destroy any lasting peace settlement. In victory, the victor should not plunder the enemy’s property that rightfully belongs to the civilians, for they did not wage war but their state did. Although supplies can be exacted from the defeated state, this does not extend to exacting reparations, for such a right can only exist for a legitimate authority and in the international state of nature none exists. The vanquished do not lose their civil rights, for to do so would impy the existence of an illegitimate punitive war.

            Finally, since the earth is initially common property, no nation has a right to colonise others’ lands. This opposes the long tradition going back to Aristotle that some people are born to serve others and which finds a manifestation even in the liberal thinker Bertrand Russell (Justice of War). However, Kant’s proscriptions against war do not rule out waging war to secure the universal code of justice his deontology demands; British imperial policy was based on such an ethic, namely that the Crown sought to bully the peoples of the world into a liberal sphere of influence through its gun boat policy in the nineteenth century.

            Kant’s prescriptions for peace are compiled in his influential Perpetual Peace (1795) in six codes.

1)      No treaty of peace shall be held valid in which there is tacitly reserved matter for a future war.

2)      No independent states, large or small, shall come under the dominion of another state by inheritance, exchange, purchase, or donation.

3)      Standing armies shall in time be totally abolished.

4)      National debts shall not be contracted with a view to the external friction of states.

5)      No state shall by force interfere with the constitution o government of another state.

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, poisoners, breach of capitulation, and incitement to treason in the opposing state.

He follows these with the conditions of perpetual peace at the national level. States should be republican, international law should be based on a federation of free states, and that universal hospitality should reign.

            The problems that remain for Kant’s system are two fold. Firstly, the probability of enacting perpetual peace through a world federation. This is an empirical concern, for which reasons Kant was pessimistic; however, modern developments since the Second World War (1939-45) have given Kantians hope. Secondly, is the graver problem of the deontological basis for his system.

            Deontological theories clash with consequentialist considerations in forming the paradigm of just war conventions. For example, if a war could be ended quicker by breaching a convention, should that convention be breached? Kantians would hold that, say, the targetting of civilians or the use of certain weapons should be outlawed and absolutely prohibited, [5]   and Dostoyevsky may cry “Would you be the architect under such conditions? Tell me honestly!” [6] , but consequentialists can focus on the benefits of breaking absolute prohibitions. For example, President Truman’s motivation for bombing Hiroshima and Nagasaki with atomic weapons, was based on the desire to avoid prolonged bloodshed, when victory could gained swiftly. A more productive approach, one that saddles the open-endedness of consequentialism and the absolutism of deontology, is offered by Michael Walzer’s argument for a sliding scale principle. Whilst the rights of civilians and the traditional just war conventions are to be upheld, Walzer argues that in cases of a ‘supreme emergency’, such rights may be broached. He upholds the threat Nazi Germany posed in World War II, a time when civilisation itself was at stake. At this time, prohibitions may be justly breached.



[1] Thomas Donaldson, “Kant’s Global Rationalism”, in Traditions of International Ethics, eds. Terry Nardin and David R. Mapel, Cambridge University Press: Cambridge, 1996, p.140.

[2] Donaldson, ibid., p.142

[3] Donaldson, ibid., p.145

[4] Cf. Useful article on an overview of the legal history of war codes by Antje Mays, “War and Peace: Of Law, Lawlessness, and Sovereignty”, Presentation for the Joint Services Conference on Professional Ethics XIX, 30th-31st January 1997, Washington DC; source:, accessed 18th February, 1998.

[5] Cf. Thomas Nagel, “War and Massacre”.

[6] Dostoyevsky, The Karamazov Brothers, quoted in Ethics, ed. Peter Singer, Oxford Readers, 1994, p.332.


© Dr Alexander Moseley, 1998