Perpetual Peace: A Philosophical Sketch

Appendix 2 plays a pivotal role in Kant’s Perpetual Peace by articulating the transcendental principle of public right. This principle provides a test by which political maxims can be judged. Importantly, this Appendix also bridges the seeming gap between moral demands and political action, reinforcing that states, constitutions, and cosmopolitan duties must be tied to universal law. 

Kant begins Appendix 2 by focusing on public right in the legal and political domains. He identifies publicity as an essential formal condition of any legal title or claim: A legal norm must be capable of being known publicly. Kant’s formula is both juridical and moral. It is juridical because it belongs to the doctrine of public right, what is permissible in law and politics. It is moral because it appeals to universal scrutiny. If a state or political actor must keep a maxim secret in order for it to succeed, then that maxim inherently contradicts the requirements for justice.

The Appendix strengthens Kant’s earlier arguments for The Moral Obligation of States by insisting that states must act under maxims consistent with publicity. A state cannot legitimately maintain secret treaties or manipulative policies because they violate the transparency required by public right. This aligns tightly with the preliminary article forbidding treaties that preserve hidden causes of future war. Here, Kant grounds the prohibition by showing how secrecy stands in opposition to justice itself.

Kant’s discussion also applies the principle to constitutional and revolutionary maxims. His work is noted for both its dismissal of revolutions and his seeming support for the French Revolution. This seeming contradiction is made clearer by his explanation. He examines whether rebellion can be morally justified. Kant asserts that this is only acceptable when the constitution is nonexistent or illegitimate. Even resistance to tyranny must be constrained by the logic of publicity and legality.

Appendix 2 also bolsters Kant’s vision for Universal Hospitality and Cosmopolitan Ethics by extending the requirement of publicity beyond domestic relations to the realm of global justice. If political maxims must withstand public scrutiny, then foreign policy, treaties, and international commitments are subject to the same test. Secret alliances or imperial conquests cannot be morally justified if their maxims could not survive open public discussion.

By rooting cosmopolitan ethics in the concept of public right, Kant asserts that universal hospitality and lawful interaction among states must be publicly justifiable. The principle of publicity provides a formal guardrail for cosmopolitan norms: States must be able to articulate their international conduct with transparency, so that citizens and foreigners alike can see whether their maxims align with universal reason and ethics.

Bridging morality and politics through the principle of public right, Appendix 2 helps resolve the tension between duty and prudence. It shows that states are more than power machines—they are moral agents whose legitimacy depends upon acting under publicly justifiable maxims which reflect individual morality. In Kant’s vision, the gradual realization of public right across states is part of humanity’s moral advance toward perpetual peace.