Subjects with autism show severe impairments in the ability to attribute beliefs to themselves and others, i.e., in their "theory of mind." An experimental investigation of the relative comprehension difficulty posed in representing different mental states is reported in this chapter, revealing that certain mental states are easier to recall than others, for all subjects. For example, see and want are easier than believe. But whereas for normal children imagine and pretend are as easy as see and want, for people with autism they are significantly more difficult. Gopnik and Slaughter's three-stage model of normal development of a theory of mind is replicated in the present experiment and found to fit the pattern of results for people with mental handicap but not the data from autism. Instead, the data from autism seem to fit a hypothesis of both deviance and delay in the development of a theory of mind.