Aggression
Aggression is the initiation of physical force against other persons or their property, the threat of such force, or fraud committed against them. The principle that such initiation is always illegitimate is the non-aggression principle, the central axiom of libertarianism in the tradition of Murray N. Rothbard.
The definition
Three elements do the work.
- Initiation. Only the first use of force is aggression. Force used to repel or to obtain restitution for an aggression already committed is defensive, and the principle does not condemn it. The whole content of the principle lies in the distinction between starting and answering.
- Physical force. The principle concerns invasions of person and property, not offence, dislike, competitive injury, or refusal to deal. A merchant ruined by a rival who serves customers better has suffered a loss but not an aggression, because nothing of his was invaded.
- Person or property. Because aggression is defined against property titles, the principle is not self-contained: it yields determinate answers only once it is settled what belongs to whom. Rothbard therefore grounds it in a theory of appropriation and self-ownership rather than treating non-aggression as a free-standing intuition.
Fraud is classed with force on the ground that it is a species of theft: the defrauder obtains property under an agreement whose terms he does not intend to fulfil, and so takes title he was never voluntarily given.
Foundations
Rothbard developed the principle from self-ownership and the appropriation of unowned resources through labour, arguing in The Ethics of Liberty that these yield a complete set of property titles and therefore a determinate answer to every question of what counts as invasion.[1]
Hans-Hermann Hoppe offered a different derivation, argumentation ethics, which holds that anyone who argues for a norm has already presupposed his opponent's control of his own body, so that a defence of aggression contradicts the conditions of its own utterance.[2]
Application to the state
The principle is the basis of the anarcho-capitalist critique of the state. Taxation takes property without the owner's consent; conscription disposes of his person; a territorial monopoly on adjudication is maintained by prohibiting competitors. Each is aggression under the definition above, and the libertarian conclusion is that the state's characteristic activities are not exempted from the rule applied to everyone else. Minarchists accept the principle but hold that a strictly limited state can be financed and maintained without violating it, and the disagreement between the two positions is largely about whether that is possible.
Disputed cases
The principle is easier to state than to apply, and the boundaries are contested within the libertarian literature. Pollution, risk-imposition, blackmail, child neglect, and the status of threats short of imminent attack are all cases where libertarians who agree on the principle disagree on the verdict, generally because they disagree about the underlying property titles rather than about non-aggression itself.