What is compatibilism, and what can neuroscience say about free will?

Compatibilism is the thesis that free will is compatible with determinism. Because free will is usually taken to be a necessary condition for moral responsibility, it is sometimes stated as the claim that moral responsibility is compatible with determinism. A 2023 review in Neuropsychologia concludes that current neuroscientific evidence is insufficient to undermine free will, and that neuroscience may not be able to answer the old philosophical questions. It may, however, help with the compatibilist question of whether people act on their own desires and reasons. [1] [2]

The problem it responds to is this: if what we do follows from the laws of nature and the state of the world long ago, then we seem unable to do otherwise and seem not to be the ultimate source of our actions. Incompatibilists conclude that freedom and responsibility are in doubt. They come in several kinds. Hard determinists think determinism is true and we are not free, while libertarians think we are free and so determinism is false. [1] [3]

Compatibilists say these worries miss the mark, but they do not agree on why. Some argue that determinism would not remove our freedom to do otherwise. Others, citing Frankfurt, Watson and Dennett, reject the idea that this freedom is needed for the kinds of free will worth wanting. Still others deny that it is connected to responsible agency at all. Scientific American describes compatibilism as the dominant view in biological, psychological, legal and medical circles, and defines it pragmatically: you are free if you can follow your own desires and preferences. [1] [4]

Studies of the brain mechanisms behind free choice leave two readings. One holds that the neural basis of choice rests on random neuronal noise, and so is indeterministic. The other holds that a free choice may result from an accumulation of unconscious contextual evidence, which leans toward determinism. If the mechanisms are deterministic, that precludes free will for incompatibilists. If they are indeterministic, that favors free will from a libertarian standpoint, though some argue randomness is not the same as freedom. [2]

The review's authors add that experimental setups have limits, and that the complexity of brain wiring and the limits of neuroscientific techniques prevent definitive conclusions. They also note that the answer on determinism may lie in fundamental physics rather than neuroscience. They caution against generalizing from experimental tasks that may not be relevant to free will. A different, more deflationary line, in a paper on what science tells us about free will, argues that we control our actions because we are our brains, and that the experience of conscious free will is the first-person view of neural activity. [2] [5]

On the compatibilist view, responsibility requires that a person acted intentionally, for reasons, as the source of the action, and with enough insight to consider the consequences. Frankfurt's example illustrates the point: a person who chooses option A on their own, while an implanted device would have forced A had they chosen B, can still be held responsible although they could not have done otherwise. [2]

Neuroscience could contribute by studying decision-making in healthy people and in conditions such as addiction, compulsion or delusion, and by examining brain regions involved in intentional action and moral judgment. The review cautions that most such studies are correlational. It says the field cannot yet reliably assess whether a particular individual meets the conditions for legal responsibility. [2]