 At the same time, if the activity of every substance—an electron, an oak tree—consists in fundamental substance causation, the worry arises whether agent causation can provide what free-will theorists who appeal to it have thought it could provide: origination, and the agent’s determining, herself, which of several open alternatives she pursues. After all, on the view in question, an electron, too, may be an undetermined determinant of what it does. Perhaps, in the end, the difference between the electron and the free agent isn’t a matter of the agent being the ultimate source of her behavior, but rather in the purposiveness involved in agent causation.