taxes payable in fiat currency are necessary for the public's acceptance of the same fiat currency for all other purposes? The account of the Lincoln era points to a moment in time when the USD became legal tender but I fail to see how its use for payment of taxes was more significant than its use for settlement of private debts. Alexander, what would constitute the proof of a theory. A theory is an explanation. theories are disconfirmed by counter-instances. There are no counter-instance disconfirming the state theory of money as far as I can see. Conversely, just because a theory has not been disconfirmed does not entail that it is confirmed. Only theories that don't fit the facts are ruled out. The various theories of money are attempts to explain a historical phenomenon in which controlled experiments are not possible and even facts are in dispute. It is possible that different explanations fit the facts. It is also possible that some combination of the present theories will turn out to be the optimal explanation, or that all of them will be disconfirmed and replaced by a better explanation. If economics were a hard science and the facts were agreed upon, then it might be possible to construct a theory that all experts would agree is optimal. That is just not the case, so you are barking up the wrong tree looking for a "proof" where one doesn't exist. The question is which explanation has the best rationale backing it