There is wide disagreement about the meaning of ordinary mental terms (such as ‘belief’, ‘desire’, ‘pain’). Sellars suggested that our use of these terms is governed by a widely shared theory, ‘folk psychology’, a suggestion that has gained empirical support in psychological studies of self-attribution and in a growing literature concerning how children acquire (or, in the case of autism, fail to acquire) ordinary mental concepts. Recently, there has been a lively debate about whether people actually ‘theorize’ about the mind, or, instead, engage in some kind of ‘simulation’ of mental processes.