Determinism is the thesis that every event, including every human choice, is the necessary outcome of prior causes together with the laws of nature. Free will is the capacity of an agent to act otherwise than they do, in a sense relevant to moral responsibility. The free will problem is the question of whether the two can both be true.
The dispute over free will and determinism asks how the ordinary conviction that people choose their actions fits with the picture of the world as a chain of causes. If a decision is itself an event in nature, and if every event follows of necessity from what came before, then it can seem that a choice was settled long before the chooser was born. Yet praise, blame, and the felt experience of deliberation all assume that the agent could have done something else. Resolving this tension is the central task of the debate.[1]
The problem is ancient, but it sharpened as the natural sciences described a world governed by exact and exceptionless law. The more the universe looked like a closed causal system, the harder it became to find room within it for an agent who originates action rather than merely transmits the effects of earlier states. NoteThe Stoics already debated fate and responsibility; the modern form owes much to the rise of mechanistic physics.
Stating the problem
The difficulty is usually framed as a conflict between three claims that each seem plausible on their own but cannot all be held together without qualification. The first is that determinism is true. The second is that free will exists. The third is the incompatibility thesis: that if determinism is true, no one acts freely. Holding any two of these forces a stance on the third, and the named positions in the debate are best understood as different choices about which claim to give up or reinterpret.[2]
A man can do what he wills, but he cannot will what he wills. commonly attributed to Arthur Schopenhauer
The main positions
Three families of view dominate the literature, distinguished by how they answer the question of whether freedom and determinism can coexist.
Hard determinism
Hard determinism accepts both that determinism is true and that determinism rules out free will, and concludes that free will is an illusion. On this view, the sense that we could have chosen otherwise is a mistake about our own situation, and practices of moral blame must be revised or reinterpreted accordingly. Some recent writers prefer the label hard incompatibilism, since they argue freedom is absent whether or not strict determinism holds, including under the indeterminism of quantum theory.[3]
Libertarianism
Libertarianism, in the metaphysical sense unrelated to the political doctrine, keeps free will and incompatibility but rejects determinism. It holds that at least some choices are not fixed by prior causes, so that the agent genuinely contributes something new. The standing challenge is to explain how an uncaused or partly uncaused choice can still be the agent's own action rather than mere chance. NoteThis is often called the luck objection: randomness seems no better suited to grounding responsibility than necessity.
Compatibilism
Compatibilism, the most widely held academic position, denies the incompatibility thesis. It argues that freedom does not require the absence of causes, only the right kind of causes. To act freely, on this account, is to act from one's own desires and reasons without external compulsion, regardless of whether those desires were themselves caused. Hume put the point by treating liberty as the power of acting according to the determinations of the will, contrasted with constraint rather than with causation as such.[4]
Why it matters
The question is not merely speculative. How a society understands responsibility shapes its justifications for punishment, reward, and reform, and the free will debate sits beneath those justifications. It also reaches into the philosophy of mind, since any account of agency must say how reasons relate to the physical events in a deliberating brain. For the relation between coherent moral judgment and considered principles, see the entry on reflective equilibrium; for the broader study of the mind that decides, see related work on the philosophy of mind indexed at PhilWiki's branches.