 Eliminativism argues that the prima facie failure to straightforwardly reduce mental kinds to neurophysiological kinds ought to lead to the elimination of mental kinds altogether (Churchland 1981, 1988). This is to claim that there are no mental natural kinds. On this view, the mental kinds in folk psychology are comparable to the kinds delineated by discredited folk theories from the past e.g., the humours in medieval medicine. The underlying principle of medieval medicine was the balancing of so-called four humours. According to the theory, illness was caused by an imbalance of these four humours. From the point of view of modern medicine this theory is radically false and so the only option is to eliminate the humours as putative natural kinds. Analogously, mental kinds ought to be eliminated in favour of those kinds uncovered by recent research in neuroscience. Eliminativists agree that human beings have invented a very successful methodology for describing their mental lives. This methodology is folk psychology, a common sense theory of how mental states are causally related to human action. However, folk psychology, they argue, is merely a heuristic device invented by human beings in order to make the explanation of behaviour easier. The posits of the theory are not real natural kinds. Once a better explanation of human behaviour in terms of neurophysiological kinds is available, then mental kinds will be eliminated.