“Modal Catapult” and the Argument for Incompatibility

Abstract

Peter van Inwagen’s modal argument for incompatibility of free will and determinism is analyzed. The argument is based on the transfer of powerlessness – no choice about p, no choice about p implies q, so no choice about q. Standard counterexamples based on inability to influence indeterministic events are first mentioned, but the main focus is on the counterexample presented by Johnson and McKay which led van Inwagen to change his definition of (in)ability to act otherwise. The danger is that this definition by itself implies incompatibilism which is dialectically improper (useless in an argument for incompatibilism). Lewis presents an objection to the first, non-modal version of the argument, so both versions are compared with respect to transfer principles for practical modalities. Lewis acknowledges that a Beta like principle leads a compatibilist to accept ability to break laws, but this ability taken in weak sense is acceptable. Begging the question is one of the main issues in discussions of the argument. One of the premises of the modal argument is really equivalent to the conclusion, but the argument does not thereby beg the question. Van Inwagen’s conclusion is, at least in principle, open to scientific refutation. In the unlikely event that causal determinism were true, we should, according to him, become compatibilists. I argue that this is not so different from Lewis (a compatibilist but not determinist), but less consistent. Nevertheless the argument indicates some paradoxical (in the sense of visual paradoxes) consequences of determinism.