 While there is little direct discussion of this question in Descartes’ work, one can find passages devoted to it in post-Cartesian philosophy. Malebranche, for example, differentiates knowledge of one’s own mind, of bodies, and of other men’s mind: the first is through consciousness, the second through ideas, and the third through conjecture (1674–5 [1980: 239]). In the case of another man’s sensations, Malebranche first considers the possibility that everyone has the same sensations when confronted with the same objects, but then notes that it can happen that “the internal fibers of the optic nerve do not produce the same sensation for different people” (Ibid, 66). Despite this possibility, Malebranche thinks there is reason to believe that God arranged things so that the same physical conditions do produce the same sensations (i.e., that nature is uniform). Nonetheless, he argues that we cannot know another’s sensations as there is “a great deal of diversity in different people’s organs of sight as well as of hearing and taste” (ibid). Writing in response to Malebranche, Arnauld (1683) insists that we do know other men’s minds through ideas: we have ideas of their bodies and must reason from these to the conclusion that they have minds. In Arnauld’s work we have, arguably, an early formulation of the argument from analogy.