Philosophy of War and Peace

What it asks

War is the deliberate infliction of death on a scale nothing else approaches. Two responses are available: that it is therefore always wrong, or that it is sometimes permissible and always constrained.

The second is the just war tradition, and it separates two questions that are genuinely independent. Whether it is permissible to fight at all - just cause, proper authority, last resort, proportionality. And what may be done within a war once begun - distinction between combatants and civilians, proportionality in each act, no means that are wrong in themselves.

Keeping those apart has a consequence people find surprising: on the traditional view, a soldier fighting for an unjust cause does no wrong by fighting, provided they fight within the rules.

The recurring problems

The moral equality of combatants. That soldiers on both sides have the same permissions is the traditional view and is what makes the law of war workable. It also implies that fighting for an aggressor is no worse than resisting one, which is very hard to defend as a moral claim rather than a legal convention. The revisionist challenge developed since the 1990s argues that individual liability, not membership of an army, determines who may be attacked.

Noncombatant immunity. Civilians may not be targeted, and may foreseeably be killed as a side effect of a legitimate attack. The doctrine of double effect carries the whole weight of that distinction, and it is doing more work than it can comfortably bear.

Supreme emergency. Whether the rules may be broken when a political community faces annihilation. Any answer here is uncomfortable.

Asymmetry. The framework assumes states with armies. It fits insurgency, occupation, drone campaigns and cyber operations badly, and those are what wars now mostly are.

How it developed

Augustine argued that a Christian may fight in a war ordered by legitimate authority for a just cause, against the pacifism of the early church. Aquinas systematised it, and Vitoria and Suarez extended it in the sixteenth century to the treatment of peoples in the Americas - the origin of the idea that the rules bind regardless of whom one is fighting.

Grotius secularised the tradition in the seventeenth century, and from there it entered international law, where it now sits as the law of armed conflict.

Walzer's Just and Unjust Wars in 1977, written against the Vietnam war, restated the tradition for a secular audience through historical cases and made it a live subject in philosophy again.

The revisionist turn since has been the most significant development in centuries, arguing that if killing in war is subject to morality at all, it must be subject to the same principles as killing anywhere else - which unravels much of what the tradition and the law take for granted.

The positions within it

Just war theory in traditional and revisionist forms; pacifism in absolute and contingent versions; political realism, which holds that war is outside morality; cosmopolitan approaches that deny states any special standing. All are in the Schools section.

Where it stands now

The revisionist argument has largely won the philosophical debate and cannot be adopted into law, because a legal regime that made a soldier's permissions depend on the justice of their cause would be unenforceable. That gap between the best moral account and the only workable legal one is the field's central live problem.

The applied work is on autonomous weapons, on the ethics of occupation and reconstruction, and on cyber operations, where the threshold for what counts as an attack is not settled.