 At several places in De Corpore, Hobbes appears to carry out the mixed-mathematics ideal by showing, with a citation, that he used a causal principle from geometry within an explanation that included details about the “quality of the subject”. For example, in De Corpore XXV, the chapter with which Hobbes began Part IV, Hobbes appears to have done just this when he explained sensation. In that explanation, he appealed both to “qualities of the subject”, such as the claim based upon experience that “we may observe… that our phantasms or ideas are not always the same” (EW I.389), and by citing and using causal principles from earlier in the work (see discussion of this explanation in Adams  2016).[4]