Can preventive war be justified?

Absolute rules fail in the hard cases that actually arise

Question: Can preventive war be justified?
Position‹3 of 3: It depends - preventative war can be justified in set conditions
Argument‹2 of 2: Absolute rules fail in the hard cases that actually arise

The argument

This argument is about how moral rules behave at the extremes. Proponents observe that an unconditional prohibition on preventive war must be applied to the worst imaginable case as well as the ordinary one: a regime that has announced its intention to destroy a neighbour, is visibly completing the means to do so, and cannot be deterred. A rule that forbids action there is not being cautious; it is requiring a state to permit its own destruction, and proponents argue that no rule commands that kind of obedience. The permissive answer fails symmetrically, on this view. A principle that allows a state to attack whenever it judges a future threat to exist, on its own assessment, in secret, is not a moral constraint but the removal of one. Proponents note that the overwhelming majority of wars described as preventive have been wars of choice, launched on evidence that did not survive scrutiny, and that any serious position has to make those wars impermissible while leaving the genuine extremity open. Proponents argue that this is why the conditional answer is the stable one. Moral reasoning about killing elsewhere takes the same form: self-defence by individuals is permitted but hedged with requirements of necessity, proportionality and immediacy, and nobody regards those qualifications as evasions. The conditional position asks of states what is already asked of persons. Because an absolute prohibition fails in the extreme case and an unconditional permission fails in the ordinary one, this argument concludes, preventive war can be justified only within carefully set conditions.

Premises

[P1]An unconditional prohibition would require a state to accept destruction visibly being prepared against it, which no moral rule plausibly demands. [P2] An unconditional permission allows any state to attack on its own secret assessment of a future threat, which removes the constraint entirely. [P3] Moral reasoning about individual self-defence already takes the conditional form, permitting it subject to necessity, proportionality and immediacy. [C] Therefore the defensible position is that preventive war is justified only under set conditions.

Counter-arguments

Opponents reply that the extreme case the argument rests on is hypothetical, while the wars actually launched under preventive reasoning have been wars of choice justified by evidence that did not survive scrutiny. They argue that a bright-line rule is valuable precisely because it does not bend to the most alarming story available at the time, and that genuine extremities can be met by deterrence, alliance and defensive preparation rather than by invasion.

Rejecting the premises

[Rejecting P1] The case is framed as a choice between accepting visible destruction and permitting prevention, which assumes there is no third course. Deterrence, alliance, mobilisation, blockade and defensive preparation all answer a visible threat without attacking first, and the premise does not consider them. [Rejecting P2] An unconditional permission is not what any opponent of preventive war defends, so the dilemma is built in part from a position nobody holds. The actual contest is between a prohibition and a conditional permission, and the premise draws its force from a third option neither side proposes. [Rejecting P3] Individual self-defence includes immediacy among its conditions, and immediacy is precisely what a preventive war lacks. The analogy therefore supports the prohibition that the argument is directed against.