The debate turns on what freedom was supposed to mean. If free will requires that, holding everything prior exactly fixed, you could still have done otherwise, then determinism plainly rules it out. Compatibilists argue that this requirement was never what we cared about, and that fastening on it produces a puzzle where there was a practical distinction we already knew how to draw.
The classical version, in Hobbes and Hume, defines freedom as the absence of impediment. You act freely when you do what you want and nothing prevents you. A prisoner in a cell is unfree; a person choosing dinner is free — and both facts are entirely compatible with every event having causes. Hume put the point sharply: the opposite of freedom is not causation but constraint. A world in which your actions had no causes would not make you freer, since your behaviour would then be random rather than yours.
That last observation is compatibilism's strongest card. Indeterminism does not obviously help. If a genuinely uncaused event occurs in your brain and you act on it, that action is not more under your control — it is less, since it did not flow from your character, values, or reasoning. Freedom seems to require that your actions be caused in the right way, by you, rather than uncaused.
Modern versions add depth. Frankfurt distinguished first-order desires — wanting a cigarette — from second-order desires — wanting to want it, or wishing you didn't. A person is free, on his account, when their will is the one they want to have. The addict who acts on a craving they wish they were rid of is unfree in a real sense, though nobody physically prevented them, and this captures something the classical account misses. Others emphasise reasons-responsiveness: an agent is free when their deliberation actually makes a difference to what they do, so that had there been good reason to act otherwise, they would have.
ObjectionsWhy incompatibilists aren't satisfied.
The manipulation argument. Imagine a person whose values and reasoning were installed by a neuroscientist before birth. They act on their own desires, without coercion, responsive to reasons — meeting every compatibilist condition — yet we hesitate to call them responsible. If manipulation undermines responsibility while satisfying the compatibilist criteria, the criteria seem insufficient. Determinism, the argument runs, is manipulation by prior causes rather than by a person.
Changing the subject. Kant called compatibilism a wretched subterfuge, and the complaint persists: it answers a question about the deep sourcehood of action by substituting a question about external constraint. Compatibilists reply that the "deep" freedom being demanded is incoherent — it would require being the uncaused cause of yourself, which nothing could satisfy.
Compatibilism is the majority position among philosophers, which is worth knowing but is not an argument. What it has going for it is that it preserves moral responsibility without requiring a metaphysics nobody can specify. What it has going against it is the persistent sense that something has been renamed rather than resolved.