The concept of an agent's causing some event seems distinct from that of an event's causing another event, and this apparent distinctness has been exploited by some philosophers of action—agent causationists—to defend an incompatibilist and libertarian account of free will. Agent causationism is associated historically with, among others, the philosophers Francisco Suárez and Thomas Reid, and in more recent times has been defended by Richard Taylor and Roderick Chisholm.
Agent Causation and Event Causation
What is indisputable is that causal statements come in at least two forms, one in which a term denoting a person or persisting object is the subject of the verb cause and one in which a term denoting a particular event occupies this role. Compare, for example, "The bomb caused the collapse of the bridge" and "The explosion of the bomb caused the collapse of the bridge." Here it seems plausible to contend that the first of these statements is elliptical, meaning something such as "Some event involving the bomb caused the collapse of the bridge," and more generally that the causation of events by inanimate objects is always reducible to the causation of those events by other events involving those objects. However, it is less evident that this sort of analysis applies in cases in which a person or other intelligent agent is said to cause some event. Sentences containing transitive verbs of action generate many such cases, because an action sentence such as "John raised his arm" clearly entails a corresponding agent-causal sentence, "John caused a rising of his arm." What seems less clear is that the latter sentence entails an event-causal sentence, "Some event involving John caused a rising of his arm," at least on the assumption that John raised his arm as a so-called basic action.
A basic action is standardly taken to be one that is not done by doing anything else. An action such as closing a door is nonbasic, because one can only close a door by doing something to it, such as pushing it. It is possible to raise one's arm as a nonbasic action—for example, by pulling on a rope attached to the arm, using one's other arm. But, it seems, there is nothing one needs to do in order to raise one's arm when one raises it in the normal way. This appears to generate a difference between the case of the bomb's causing the collapse of the bridge and that of John's causing the rising of his arm: the bomb caused the collapse by exploding, but John, it seems, did not cause the rising by doing anything else. Consequently, it is not evident that there was any event involving John that could be said to have caused the rising in the way that the explosion of the bomb can be said to have caused the collapse of the bridge. In this case it appears that a statement of agent causation is not reducible to one of event causation.
Philosophers who favor a volitionist theory of action may dispute this suggestion. They may urge that there is in fact something that John did, and by doing this he raised his arm—on the assumption, at least, that he did so voluntarily. Namely, John willed to raise his arm. It was by willing to raise his arm that he did raise it, and so it might be said that the agent-causal statement, "John caused the rising of his arm," is true only in virtue of the truth of the event-causal statement, "John's willing to raise his arm caused the rising of his arm." However, volitionism is now a minority position in the philosophy of action—in contrast with its heyday in the seventeenth and eighteenth centuries—because many philosophers are skeptical about the existence of volitions as a supposedly distinctive class of mental events. Proponents of the irreducibility of agent causation to event causation may take comfort in this fact, although they still have to face another and more prevalent kind of critic: the proponents of mainstream causal theories of action. These critics contend that intentional actions have mental causes of another sort—the onsets of states of belief and desire. While these philosophers may concede that there is no action by doing which John caused his arm to rise, they still contend that there was an event involving John that caused the rising of his arm—to wit, the onset of his desire to raise it and, perhaps, his belief that by raising it he could achieve some further desired end. This event was not an action of John's, to be sure, but it was nonetheless an event involving him that, like the exploding of the bomb, seems to explain how the effect he caused was brought about.
Agent Causationism and Free Will
Agent causationists—that is, philosophers who maintain the irreducibility of agent causation to event causation—are opposed to mainstream causal theories of action, not least because the latter seem inhospitable to libertarianism (the doctrine that free actions lack determining causes in the form of antecedent events which causally necessitate their occurrence). Proponents of such mainstream theories are typically compatibilists concerning the relationship between free will and determinism. Agent causationists, in contrast, standardly hold that certain events caused by agents are not caused by any antecedent events, or at least that these certain events lack sufficient causes in the form of antecedent events. Some agent causationists maintain that the events in question are bodily movements—such as the rising of an arm—when these are the products of basic actions. Others maintain, perhaps more plausibly, that the events in question are certain neural events that are the causal precursors of bodily movements. Yet others seek to combine agent causationism with a form of volitionism by contending that what agents cause directly are their own volitions, choices, or endeavors. Thus, agent causationism is not necessarily opposed to volitionism, only to certain versions of it.
Common to all standard forms of agent causationism, however, is the doctrine that at least some cases of an agent A 's causing an event e do not consist in e 's being caused by any antecedent event involving A. This doctrine seems to help the case for libertarianism in the following way. The libertarian wants to say that in a case of free action, an event e occurs that lacks a sufficient cause in the form of antecedent events. But this prompts the objection that e would then be a mere chance event—such as the spontaneous decay of a radium atom—and as such would not exhibit the kind of freedom associated with an action for which an agent may be held morally responsible. The agent causationist may respond by urging that there is a significant difference between the decay of a radium atom and a case of free action because in the latter an event e occurs that, while lacking a sufficient cause in the form of antecedent events, still has a cause in the form of the agent whose action it is. A radium atom does not cause itself to decay, but a free human agent may cause him or herself to act in a certain way, according to agent causationism. Free agents, according to this conception, are unmoved movers or ultimate initiators of certain trains of events. And it is in having this capacity for initiation that their freedom allegedly lies, for it supposedly enables free agents to intervene in and affect the ongoing stream of events in which natural physical processes consist. Free agents' capacity for initiation is conceived to be a "two-way power"—a power either to cause or to refrain from causing an initial event of an appropriate kind.
Objections to Agent Causationism
Not surprisingly, agent causationism is subject to many criticisms—in particular from philosophers who advertise their own position as being "naturalistic"—and is charged with being mysterious and incompatible with the modern scientific worldview as revealed by physics and biology. More specifically, one popular objection is that agent causationism is committed to some form of substance dualism in the philosophy of mind, which in the eyes of most naturalistic philosophers would be enough to condemn it. However, whereas many agent causationists may in fact be substance dualists, it is not clear that their agent causationism requires them to be.
A more cogent objection to agent causationism, forcibly expressed by C. D. Broad, is that the agent causationist cannot explain why an event supposedly caused irreducibly by an agent should occur when it does (since agent-causes, unlike event-causes, are not datable items). The collapse of the bridge occurred when it did because the explosion, which was its cause, occurred when it did. But why should the many different events supposedly caused by a single agent during his or her lifetime have occurred when they did? One possible answer is that these events also have contributory causes in the form of antecedent events occurring at different times, even though each of them additionally requires causation by the agent for its occurrence. Another possible response, consistent with the first, is to appeal to temporal factors included in the agent's reasons for causing the various different events in question. (Agent causationists typically repudiate the doctrine that reasons are causes, and distinguish between reasons-explanations and causal explanations—or at least they deny that an agent's reasons, in the form of certain beliefs and desires of the agent, are part of a sufficient event-cause of the agent's action.)
Others may object that agent causationism does not really assist the case for libertarianism in the way it is alleged to for the following reason. Suppose, for the sake of argument, that instances of irreducible agent causation really do occur, and that sometimes it is the case that an agent A causes an event e in this irreducible fashion, while e lacks a sufficient cause in the form of antecedent events. It was suggested earlier that this still allows us to say that e was not just a chance event, because it was caused by A. However, what about the event of A 's causing e ? It would seem that this event must either possess or lack a sufficient cause in the form of antecedent events. If the former, then it is hard to see how libertarianism is saved. If the latter, then it would seem that A 's causing e is itself just a chance event and so once again provides the wrong sort of freedom for moral responsibility.
Once more, various replies are available. One is simply to deny that A 's causing e qualifies as an event and as such is something eligible to possess a cause. After all, it seems odd to think of one event's causing another as itself being an event, just as it may be deemed equally odd to think of an agent's causing an event as itself being an event. Another possible reply is that when there is an instance of agent causation—A 's causing e —the agent A is not only the agent-cause of e but is also, by virtue of that fact, the agent-cause of this instance of agent causation. If this is the case, then the instance of agent causation is excluded from being a mere chance event for the same reason that the event e is thus excluded.
It does not appear, on close inspection, that there is anything incoherent in the notion of irreducible agent causation, but whether it really helps to solve the problem of free will and whether it is consistent with current scientific theories in physics and biology are questions that still remain open to further debate.
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E. J. Lowe