The rise of cognitive psychology has heralded a revival of interest in the mind-body problem. As a heuristic, Hyland (1985) suggested that mind terms and body terms be thought of as complementary descriptions of the same event. Complementarism precludes causal relations between mental and physiological events, and instead posits identity relations between these two types of variables. Independently, Kirsch (1985) proposed that for all causal sequences linking one mind state to another, there is a corresponding causal sequence of physiological states. Rather than being mind-body philosophies, complementarity and causal isomorphism are shown to be logical consequences of virtually all monist philosophies, including those that are currently most prominent. Their heuristic value is demonstrated with respect to empirical questions about psychophysiological phenomena.