In libertarian political philosophy, a night-watchman state is a model of a state whose only functions are to provide its citizens with the military, the police, and courts, thus protecting them from aggression, theft, breach of contract, fraud, and enforcing property laws; therefore only to act as an enforcer of the non-aggression principle. The nineteenth-century UK has been described by historian Charles Townshend as standard-bearer of this form of government among Western countries.
The term Nachtwächterstaat was coined by German socialist Ferdinand Lassalle in an 1862 speech in Berlin. He criticized the bourgeois liberal limited government state, comparing it to a night-watchman whose sole duty was preventing theft. The phrase quickly caught on as a description of capitalist government, even as liberalism began to mean a more involved state, or a state with a larger sphere of responsibility.Ludwig von Mises later opined that Lassalle tried to make limited government look ridiculous, but that it was no more ridiculous than governments that concerned themselves with "the preparation of sauerkraut, with the manufacture of trouser buttons, or with the publication of newspapers". Proponents of the night-watchman state are minarchists, a contraction of "minimum" and -archy. Arche (; Ancient Greek: ?) is a Greek word which came to mean "first place, power", "method of government", "empire, realm", "authorities" (in plural: ), "command". The word "minarchist" was coined by Samuel Edward Konkin III in 1980.
Minarchists generally justify the state on the grounds that it is the logical consequence of adhering to the non-aggression principle. They argue that anarchism is impractical because it is not sufficient to enforce the non-aggression principle, because the enforcement of laws under anarchism is open to competition. Another common justification is that private defense and court firms would tend to represent the interests of those who pay them enough.
Some minarchists argue that a state is inevitable, thus believing anarchy to be futile. Robert Nozick, who publicized the idea of a minimal state in Anarchy, State, and Utopia, argued that a night-watchman state provides a framework that allows for any political system that respects fundamental individual rights, and therefore morally justifies the existence of a state.