A rule can never be binding just because some person with physical power wants it to be so. He must have authority to issue the rule or it is no rule, and such authority can only come from another rule which is already binding on those to whom he speaks. That is the difference between a valid law and the orders of a gunman.

Builds on: "Obligation under rules differs from mere coerced obedience to orders."

Ronald Dworkin, Ronald Dworkin - The Model …, loc. 48