Perpetual Peace: A Philosophical Sketch

Kant views a government’s constitution as a rational framework through which a state organizes the moral and political life of its citizens. A constitution expresses the relationship between freedom and law—two central pillars of Kant’s moral philosophy. Kant argues that a “republican constitution” is the only legitimate form of government because it aligns political authority with the autonomy of individuals.

Cosmopolitan right, in Kant’s Perpetual Peace, is the third category of law in his moral-political framework, alongside civil and international rights. It governs the relationship between individuals and foreign nations, emphasizing a minimal but universal moral obligation for respect and hospitality. For the philosopher, cosmopolitan right emerges from the shared ownership of the earth’s surface. Thus, every human being has the “right to visit” other lands without hostility, so long as they act peaceably. This right is not a license for colonization or domination, which Kant explicitly condemns. Instead, cosmopolitan right forms the ethical foundation for peaceful interaction across borders and cultures.

Central to Perpetual Peace is Kant’s proposal for a voluntary federation of free, republican states united by shared laws and a moral commitment to peace. Unlike a global superstate, this federation preserves the sovereignty of each member while creating a framework for lawful international relations. Its purpose is to prevent war by replacing the anarchy of competing powers with a system of universal law. This idea predates modern institutions such as the League of Nations and the United Nations. Kant’s notion of the federation represents a bridge between individual morality and world peace.

Kant’s principle of hospitality arises from the idea that the Earth belongs collectively to all human beings, and no person has an inherent right to exclude another from the surface of the planet. Hospitality is a key element of his cosmopolitan philosophy. Kant carefully distinguishes between the right to visit and the right to settle: Hospitality ensures safety and respect, not colonization and appropriation. In this distinction, Kant condemns European imperial practices, which used travel and trade as pretexts for conquest. Hospitality is, therefore, an ethical test of a state’s commitment to reason and moral law.

Perpetual peace describes longstanding peace within a state. Kant’s essay outlines prescriptions that he argues will lead to perpetual peace. The philosopher does not imagine peace as the mere absence of war but as an enduring condition sustained by just institutions and rational cooperation. The term “perpetual” signals that true peace must be grounded in universal laws that make war impossible in principle. Importantly, Kant views peace as a moral duty rising from the categorical imperative: If war cannot be universally willed without contradiction, reason demands peace.

Kant’s definition for republicanism refers to a constitution with separation of powers, representative lawmaking, and the rule of law. A republican constitution is used by a state governed by laws that preserve individual freedom and subject rulers themselves to those same laws. Kant does not view a true republic as a democracy, which he sometimes viewed as prone to despotism when majority rule suppresses minority rights. He suggests that a republic is grounded in representation, and that the state must ensure that citizens—who bear the costs of war—have a voice in deciding whether or not to wage it.