In 1969 Harry Frankfurt published his hugely influential paper ‘Alternate Possibilities and Moral Responsibility’ in which he claimed to present a counterexample to the so-called ‘Principle of Alternate Possibilities’ (‘a person is morally responsible for what he has done only if he could have done otherwise’). The success of Frankfurt-style cases as counterexamples to the Principle has been much debated since. I present an objection to these cases that, in questioning their conceptual cogency, undercuts many of those debates. Such cases all require a counterfactual mechanism that could cause an agent to perform an action that he cannot avoid performing. I argue that, given our concept of what it is for someone to act, this requirement is i...