  Although most psychologists would without hesitation accept the causal interaction of minds and bodies, a small but growing number of empirical researchers have insisted that the evidence supports some version of epiphenomenalism, the thesis that mental states, while caused by physical happenings, exert no efficacy in return. Wegner, a psychologist, contends that accumulated empirical evidence overwhelmingly supports epiphenomenalism, at least with respect to conscious willing (Wegner 2002, 2004). He draws on influential work by Libet (1985, 2001, 2004) and others to argue that conscious intending is itself a product of nonconscious processes that do the real causal work, so that free will is “an illusion”. If Wegner and his colleagues are right, these results could have ancillary implications for the physical efficacy of mental states generally.