QuestionsWhat is a just society?Perpetual peace: republics, a federation of free states and universal hospitality
What is a just society?One humanity

Perpetual peace: republics, a federation of free states and universal hospitality

The perpetual peace project

Immanuel Kant 1724 · 1804Set the limits of reason; act from duty.
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What it claims

To establish perpetual peace, each state must be a republic, states must form a federation and foreigners must be protected by hospitality; and this aim is no chimera.

Why

Peace is not natural and must be established: in a republic, those who pay for war must consent to it.

The same idea through history
Marcus Aurelius170All humans are fellow citizens of one city, the world: the ancient idea of a right that goes beyond state borders.
Charles-Irénée Castel, abbé de Saint-Pierre1713The first great modern plan: a permanent union of the European states, with a common arbiter, to guarantee peace.
Immanuel Kant1795He turns it into an argument of legal philosophy: three levels of public right and a guarantee by nature.
In short

"Perpetual peace: republics, a federation of free states and universal hospitality" is an argument by Immanuel Kant (Perpetual Peace (Zum ewigen Frieden), 1795, 1795) on the question "What is a just society?" (answer: one humanity). Its claim: To establish perpetual peace, each state must be a republic, states must form a federation and foreigners must be protected by hospitality; and this aim is no chimera. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 8 premises. AskPhilosophy presents 3 objections, 1 of them with a documented reply, and the original text behind each premise, checked word for word.

Perpetual Peace (Zum ewigen Frieden), 1795
Valid

In 1795 Europe is at war and the French Revolution has just shaken it. Kant proposes a real peace treaty, not a mere truce. His idea: peace is not the natural state between humans, it must be established, and only through law. From this he draws three requirements, one for each level of public right. Within, each state must have a republican constitution. Between states, there must be a federation of free states, not a world state. Between individuals and foreign states, right is limited to hospitality: not being treated as an enemy when arriving peacefully. He adds that nature itself pushes this way. It is the "universal" camp because right here holds for all human beings, beyond borders. The P1..P8 → C form is our reconstruction.

P1Peace is not the natural state among humans, which is rather a constant threat of war. Peace must be established, and this can only be done in a state governed by law.
P2Within a state, the only constitution that comes from the idea of the original contract is the republican one, founded on the freedom of its members, their subjection to a common legislation and their equality as citizens.
P3In a republic, citizens must consent to war, although they would pay for it with their persons and their property: they will think twice. A ruler who owns the state loses almost nothing by it.
P4Between states, which are like individuals in a state of nature, right requires a federation of free states that does not form a single state: a state of nations would be self-contradictory, since several peoples united in one state would make only one people.
P5Between foreigners and states, cosmopolitan right is limited to hospitality: the right of a stranger, arriving peacefully, not to be treated as an enemy. It is not a right to be received as a guest.
P6Nature itself works for peace: it makes concord spring from human discord, even against their will, through the war that scatters peoples and forces them to give themselves laws.
P7The commercial spirit cannot coexist with war and sooner or later takes hold of every nation: states are pushed by interest to promote peace.
P8This guarantee of nature does not allow us to predict peace, but it is enough from a practical point of view: it makes it a duty to work for this end, which is therefore no chimera.
Therefore, to establish perpetual peace, each state must be a republic, states must form a federation and foreigners must be protected by hospitality; and this aim is no chimera.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
The argument is valid as Kant writes it, with no hidden premise. P1 states that peace goes through law; P2 to P5 say what law requires at each level; P6 to P8 add that nature makes this aim realistic. The whole debate is therefore about the premises. P4 is the most attacked: can a federation with no power above states really prevent war? Hegel says no. P2 is also disputed: must all states be republics? Rawls doubts it. And P1 assumes that peace is a project of law, which Schmitt denies.
Analogy. In a block of flats, peace between neighbours does not come from goodwill alone. You need house rules (internal right), common rules between the buildings on the street (federation), and the rule that a peaceful visitor is not thrown out (hospitality). But no one has to merge the whole street into a single building.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Hegel (no praetor between states) 1820 · attacks premise 4

Between states there is no praetor, that is, no judge above them, at most referees and mediators, and even then only if particular wills so wish. The Kantian idea of perpetual peace through an alliance of states that would settle every dispute assumes that states are in agreement, but this agreement itself rests on their sovereign will, hence on chance (Philosophy of Right, § 333, Remark).

Kant replies
Kant (what he had already written, twenty-five years before Hegel) 1795 · Kant admits that the federation is only a "negative substitute"
Kant knows the ideal would be a universal republic, but states do not want it. Failing that, only a negative substitute remains: a permanent alliance that averts war and keeps spreading. He adds that one will always have to fear that it breaks down (Perpetual Peace, second definitive article).
Hegel 1820
Hegel draws the consequence: when the particular wills of states find no agreement, the dispute can be settled only by war. And since a state can put its honour in each of its interests, it is impossible to say beforehand which offences would justify war (Philosophy of Right, § 334).
Where the debate stands (our summary)Kant and Hegel agree that no judge imposes itself on states today. Kant holds that reason nevertheless obliges us to create this federation, even if it remains fragile; Hegel holds that an agreement based on sovereign wills remains a mere ought. The core disagreement is whether a legal order between states can hold without a power to enforce it. An open point, with no widely accepted answer. Our summary.
C
Carl Schmitt 1932 · attacks the conclusion

For Schmitt, the political is defined by the possibility of distinguishing friend from enemy, and war is its extreme eventuality. A world where this possibility was abolished by a universal legal order would no longer have politics: it would be depoliticised. He also suspects that in the name of humanity a state may deny its adversary the status of an ordinary enemy and wage unlimited war on him (The Concept of the Political, 1932).

no reply
No reply possible: objection raised in 1932, after the author's death (1804).
Where the debate stands (our summary)Schmitt rejects the very idea of peace through universal law; Kant holds it to be a duty of reason. Both look war in the face, but one makes it the limit of the political, the other the evil that law must abolish. A core disagreement, with no widely accepted answer. Our summary.
John Rawls 1999 · attacks premise 2

Rawls takes up the Kantian idea of a society of free peoples, but not the requirement that all be republics. He accepts that a "decent" people, non-liberal and hierarchical but respectful of human rights and of peace, may be a full member of that society. Liberal peoples must tolerate it, not force it to become a democracy (The Law of Peoples, 1999).

no reply
No reply possible: objection raised in 1999, after the author's death (1804).
Where the debate stands (our summary)Rawls and Kant agree on the federation and on rejecting a world state. They differ on the condition of entry: a republic for Kant, a "decent" people is enough for Rawls. The debate is about toleration of non-liberal regimes. An open point, with no widely accepted answer. Our summary.