Sometimes people say that you can't really have law under anarchy. But, inspired by a recent episode of Divided Argument (dividedargument.com/episodes/s…), I think American constitutional law is a counterexample.

Constitutional law looks and acts like law that constrains the federal and state governments. But there isn't a super-government that rules over the federal government that constitutional law appeals to, where if the federal government disobeyed rulings the super-government would punish them. Instead, courts rule on constitutional law, and the federal government follows, probably because the individual humans who work for the government by and large think that's the best for them in the long run.

This doesn't prove that law for humans could work without a state. There are way more humans than there are governments, so even a small rate of people ignoring courts is quite bad (where a small rate of governments ignoring courts is tolerable). And of course there are a bunch of other disanalogies. But it does indicate that stateless law is a conceivable thing.