A notion prominent in the work of Ryle. A category mistake arises when things or facts of one kind are presented as if they belonged to another. Someone would make a category mistake if after being shown all the battalions and regiments she wished to be shown the army. Ryle believed that a Cartesian theory of mind depended on the category mistake of reifying mental events, instead of seeing mental descriptions as just one kind of description of persons and their dispositions. Thinking of beliefs as in the head, or numbers as large spatial objects, or God as a person, or time as flowing, may each be making category mistakes.