A philosophical tradition going back to Descartes assumed that human beings have an indubitable consciousness of their own minds but that knowledge of other minds was at best inferred. What they failed to see was that the consciousness, the felt experience that could not be doubted, was not the same as introspection. William James, as mentioned in Chapter 4, was guilty of this conflation. Introspection is enabled by mental concepts used in ascribing mental states to others. Put simply, introspection is self-ascription; one cannot introspect without linguistic concepts of mind. As Montgomery (2005, p. 120) pointed out in regard to children’s acquisition of theory of mind, “introspective knowledge [plays a much smaller role] in mental concept formation than is sometimes claimed.” Montgomery’s concern has been ignored by those influenced by Simulation Theory.