Libertarian Free Will

Core Idea

Libertarianism about free will is the incompatibilist view that agents do have genuine free will, which requires that determinism is false. On this view, free actions are neither fully determined by prior causes nor are they random — they originate in the agent as a genuine cause. Agent causation theories (Chisholm, O'Connor) hold that persons are irreducible causal powers that initiate action from themselves. Event-causal indeterminist views locate indeterminacy in neural processes but struggle to explain why quantum randomness amounts to control rather than mere chance. Libertarianism is empirically constrained by physics and neuroscience.

How It's Best Learned

Read Chisholm's 'Human Freedom and the Self' for the agent-causation version, then Kane's The Significance of Free Will for an event-causal approach. Assess whether either avoids the 'luck objection' — that indeterminate events are lucky, not free.

Common Misconceptions

• Libertarian free will is not the political philosophy of libertarianism; it's a position in metaphysics.
• Appealing to quantum indeterminacy doesn't automatically solve the problem: random events are not the same as self-determined actions.

Explainer

From your study of free will and determinism, you understand the central challenge: if every event — including every brain state and decision — is fully determined by prior physical causes plus the laws of nature, then in what sense could you have done otherwise? The incompatibilist answers that you couldn't have, and draws the conclusion that genuine free will is incompatible with determinism. At this fork in the road, there are two incompatibilist responses: hard determinism (determinism is true, therefore we lack free will) and libertarianism about free will (we do have free will, therefore determinism must be false for at least some actions).

Libertarianism thus stakes a bold empirical and metaphysical claim: the causal history of a free action is not fully deterministic. But this immediately faces what is sometimes called the luck objection. If the decision is not fully determined by prior causes, then there is some element of indeterminacy at the moment of choice — which seems to mean the decision is, to that degree, random. And random events are not controlled by the agent. They simply happen. So replacing determinism with indeterminism seems to trade one threat to free will (compulsion by prior causes) for another (mere chance). The challenge for any libertarian theory is to explain how indeterminism can be freedom rather than luck.

Two main strategies have emerged. Agent causation theories (associated with Roderick Chisholm and Timothy O'Connor) hold that free actions are caused by the agent *as a substance*, not by any prior event. The agent is an irreducible causal power — a locus of origination — that initiates action from itself without being reducible to the chain of physical events. This preserves the intuition that the self genuinely causes its choices, but it faces the challenge of explaining how agent causation fits into the physical world without violating causal closure. Event-causal indeterminist theories (associated with Robert Kane) locate indeterminacy in specific neural processes — moments where quantum-level fluctuations leave the outcome genuinely open — and argue that the agent's character and deliberation are causally engaged with these processes, so the outcome, though not determined, is authentically the agent's own.

Your prerequisite in modal logic is relevant here: libertarians often appeal to the "could have done otherwise" requirement for free will — the claim that in the actual world, with all the same prior history and laws, the agent might have chosen differently. Modal logic provides the tools for being precise about this claim. On a libertarian reading, in the possible worlds adjacent to the actual one (same prior history, same laws), some worlds contain the agent deciding A and others contain the agent deciding B — genuine branching in the space of possibilities, not just branching due to ignorance about a fixed outcome. Whether physics and neuroscience actually support this picture remains an open empirical question, and it is one reason libertarian free will carries a distinctive empirical burden that compatibilist theories do not.