Since the ancient Greeks, one of the most provocative and oft-discussed questions in philosophy has been whether we have free will in determining the course of our actions, or whether our actions are determined by forces beyond our control. Before the advent of secular thought, those forces might have been identified as the whims of the gods, though the tradition of naturalism in Western thought goes back at least as far as the Milesian School of Greek Philosophy, in the 6th century B.C. In more recent times as the cognitive sciences have developed, it has seemed increasingly likely that our brains work along deterministic lines (or, if quantum effects are non-negligible, at the very least along mechanical lines). So a new debate has arisen: are the concepts of determinism (or naturalism or mechanism) when applied to the brain sciences logically compatible with free will? So some of the attention has shifted from the debate between the “determinists” and the “anti-determinists”, to that between the “compatibilists” and the “anticompatibilists”.

Two declared opponents in this debate are Peter van Inwagen (author of An Essay on Free Will, Oxford University Press, 1983) and Daniel C. Dennett (author of several books including Elbow Room, MIT Press, 1984, which I will be referencing here). Each argues for his conclusion from premises he regards as antecedently plausible, with van Inwagen taking the anti-compatibilist line and Dennett the compatibilist. As van Inwagen is the more precise arguer of the two, I will use his work as the starting point for this discussion. Like Dennett, whose book is subtitled “The Varieties of Free Will Worth Wanting”, he is arguing that we do have free will.Where they differ is on the nature of its relationship to determinism. Van Inwagen presents three premises in his main argument : that free will is in fact incompatible with