Free will

Free will refers to the human capacity to select among possible actions, to govern one's behavior in a way that grounds moral responsibility, or to act as the genuine origin of one's deeds. Different philosophical traditions emphasize different aspects of this idea, and debates center on whether such freedom can exist alongside physical determinism, divine foreknowledge, or other limitations. The concept is tightly bound to notions of moral desert, praise, blame, and other judgments that only make sense for actions that are freely chosen. It also relates to advice, persuasion, deliberation, and prohibition. Traditionally, only freely willed actions are considered worthy of credit or blame. Whether free will exists, and what follows from its existence or absence, ranks among philosophy's longest-running disputes.

Some thinkers define free will as the ability to make choices not determined by prior events. Determinism, however, holds that the natural world follows cause-and-effect relationships, allowing only one possible course of events—a view inconsistent with a libertarian model of free will. This issue was recognized in ancient Greek philosophy and remains a major focus. The position that free will and determinism are incompatible is called incompatibilism. It includes metaphysical libertarianism, which claims determinism is false and free will is possible, and hard determinism or hard incompatibilism, which claims determinism is true and free will impossible. Another incompatibilist view, illusionism or hard incompatibilism, argues that both determinism and indeterminism (randomness) are incompatible with free will, so free will is impossible regardless of whether determinism is true.

Compatibilists, by contrast, hold that free will and determinism can coexist. Some compatibilists—hard compatibilists—even argue that determinism is necessary for free will and agency, because choice involves preferring one action over another, which requires understanding how choices will turn out. Different compatibilists define "free will" in very different ways, and thus identify different constraints as relevant. Classical compatibilists saw free will as simply freedom of action: one is free if, had one wanted to do otherwise, one could have done so without physical hindrance. Many contemporary compatibilists instead treat free will as a psychological capacity—for example, the ability to direct behavior in ways responsive to reason or open to sanction. Still other conceptions of free will exist, each with its own concerns, but all share the common feature of not seeing physical determinism as a threat to free will.

The problem of free will appears in ancient Greek philosophical literature. The compatibilist notion has been attributed to Aristotle and Epictetus: they held that control over actions came from nothing hindering us from doing or choosing something. According to Susanne Bobzien, the incompatibilist notion may first appear in Alexander of Aphrodisias, who argued that control comes from being causally undetermined in decision, allowing free choice between doing or not doing. The term "free will" (liberum arbitrium) was introduced by Christian philosophy. Until the Enlightenment proposed its own meanings, it traditionally meant a lack of necessity in the human will—so "the will is free" meant "the will does not have to be as it is." This requirement was accepted by both incompatibilists and compatibilists.

The underlying questions are whether we have the control over our actions that we feel we do, and if so, what kind or degree of control we exercise over voluntary behavior. These ancient problems predate the early Greek Stoics, and some modern philosophers still lament the lack of progress. On one hand, humans have a strong sense of freedom, agency, and self-determination, leading to a natural belief in free will. On the other hand, that intuitive feeling could be mistaken. Reconciling the evidence that conscious decisions are causally effective with the view that the physical world is fully explained by physical law is difficult. The conflict between felt freedom and natural law arises when either causal closure (no physical event has a non-physical cause) or physical determinism (the future is entirely determined by preceding events) is asserted. This puzzle is known as the problem of free will or the dilemma of determinism, and it also creates a moral dilemma about assigning responsibility for actions if they are entirely caused by past events. Compatibilists maintain that mental reality is not itself causally effective. Classical compatibilists addressed the dilemma by arguing that free will exists as long as humans are not externally constrained or coerced.