 It was against this background that Harry Frankfurt proposed his famous counterexample to the “Principle of Alternate Possibilities” (a person is morally responsible for what he has done only if he could have done otherwise). Frankfurt wanted to defend the claim that moral responsibility is compatible with determinism without having to defend the claim that the ability to do otherwise is compatible with determinism. His strategy took the form of an ingenious thought experiment that was supposed to show that no matter how you understand ability to do otherwise—whether you are a compatibilist or an incompatibilist—you should agree that the possession of this ability is not a necessary condition of being morally responsible (Frankfurt 1969).