Agent causation is the thesis that free actions are caused not by prior events but by the agent as a substance — the person herself originates the causal chain without being determined by antecedent states. Chisholm introduced the distinction: standard event causation is a relation between events (the striking caused the lighting), while agent causation is a relation between a substance and an event (the agent caused the decision). Agent causation is the core metaphysical commitment of many libertarian theories of free will, because it promises a kind of origination that is neither determined nor random. Critics object that agent causation is mysterious — it posits a sui generis causal power that resists integration with the natural sciences — and that it faces the problem of timing: what explains why the agent acts at one moment rather than another?
Read Chisholm's 'Human Freedom and the Self,' then O'Connor's Persons and Causes. Focus on the key objection: if agent causation is not event causation, how does it interface with the physical causal order?
From your study of free will and determinism, you know the central tension: if every event is caused by prior events according to natural laws, then your choices appear to be just more links in a causal chain stretching back before you were born. From your study of causation and causal relations, you know that standard philosophical accounts analyze causation as a relation between *events* — the striking of the match caused the lighting of the flame, one event producing another. Agent causation is a proposed escape from this picture: not all causation is event causation. Some causation, specifically the causation involved in free action, has a *substance* — a person — as the cause rather than an event.
Roderick Chisholm, who developed the most influential formulation of agent causation, drew the distinction sharply. Event causation is a relation between events: event E1 causes event E2. The entire physical world operates this way — one state of affairs gives rise to the next. Agent causation is a relation between a substance and an event: the *agent* (the person, not any event occurring in or to the person) causes the decision. When you freely raise your arm, on this view, you — not your brain state, not your desires, not your prior intentions — are the direct cause of the raising. This gives you a kind of origination: you start a new causal sequence rather than merely transmitting an existing one.
Why does this matter for free will? Because it promises to escape both horns of the classic dilemma. If your choices are determined by prior events, you are not free (the determinist's complaint). If your choices are not determined — if they happen randomly — you are not in control of them either, and randomness is no better than compulsion. Agent causation offers a third option: your choices are neither determined by prior events nor random, because *you* are their cause, and you are not an event. The self is a substance with its own causal power, irreducible to the event-causal order. This is the core metaphysical commitment of libertarianism about free will (not the political view, but the view that free will requires the ability to have done otherwise in a genuinely undetermined sense).
The most serious objection is the problem of intelligibility. What exactly does it mean for a substance — rather than an event — to cause something? In event causation, we can at least point to regularities, counterfactuals, and mechanisms. In agent causation, we seem to be positing a sui generis causal power that operates outside the ordinary physical world, and critics ask: how does this power interface with the physical causal order? If your neural states are not causally sufficient for your decision, something must bridge the gap — but what, and how? This is sometimes called the problem of causal integration: agent causation seems to require that the agent inject a causal contribution into the physical world without being subject to physical law, which appears to violate the causal closure of the physical domain.
A related challenge is the timing problem: if you, as an agent, are the cause of your decision, what explains why you decided at this moment rather than that one? In event causation, timing is explained by the timing of the causing event. In agent causation, there seems to be no explanation — the agent simply acts when they act. Critics see this as leaving too much unexplained; defenders reply that this is precisely what origination requires. Whether that is an acceptable cost or a sign that agent causation is incoherent is the central dispute that divides libertarians from both compatibilists and hard determinists.
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