Philosophy
The Metaphysics of Free Will and the Principle of Alternative Possibilities
Quick fact
In Harry Frankfurt's famous thought experiments, an agent can be morally responsible for an action even when they could not have done otherwise—because the interfering mechanism never actually intervenes.
Why this is interesting
You are about to press a button, but a psychologist has secretly been scanning your brain. Would you be morally blamed for pressing it, even if you genuinely had no other option?
Read the full explanation
Understanding The Metaphysics of Free Will and the Principle of Alternative Possibilities
Imagine you are deciding whether to raise your hand. Normally, we think you are responsible for raising it because you could have chosen not to. This intuition is captured by the Principle of Alternative Possibilities (PAP), which says: a person is morally responsible for an action only if they could have done otherwise. For centuries, this principle seemed obvious. If someone is forced at gunpoint, we do not praise or blame them because they had no real choice. But what if you are not forced in fact, yet the option to do otherwise is somehow blocked? Harry Frankfurt challenged this. He imagined a case where a neuroscientist has secretly implanted a device in your brain that would force you to raise your hand if you decided not to. But you decide to raise your hand on your own. The device never kicks in. You had no alternative—because if you had tried to not raise, you would have been forced anyway—but you did act of your own free will. Frankfurt said you are morally responsible, and so PAP must be false.
A deeper explanation
Frankfurt's counterexample works by separating the condition of having an alternative from the condition of being the genuine source of your action. In his scenario, the agent does not have an alternative, but the agent's own deliberation and decision cause the action. Crucially, the backup mechanism that would have forced the action is never triggered. This shows that responsibility does not depend on the mere existence of a counterfactual possibility—what would have happened had the agent tried to act differently—but on the actual causal history of the action. This has profound implications for compatibilism, the view that free will and moral responsibility are compatible with determinism. If PAP is false, then determinism does not automatically undermine moral responsibility, because even if all your actions are determined, you might still be the source of them in the relevant sense. Critics of Frankfurt argue that his cases are ultimately flawed, perhaps because the agent's ability to do otherwise is not completely removed without altering the mental life of the agent. But the principle that responsibility requires alternative possibilities has been profoundly shaken, and the debate continues today.