In this chapter I try to strengthen the results of the preceding chapter by looking at how Aristotle attempts to negotiate the issues identified there: whether knowledge is [1] “like by like” and [2] “alteration.” I argue that this is the work of De Anima II 5, a difficult text which has attracted a considerable literature, much of it animated by the question of whether Aristotle conceives of perceiving as something purely “spiritual.” Though I argue (as have others) that this question is not settled by II 5, my primary object is to present a reading on which its main business is to clarify the “grammar” of perception, so as to respect the fact that perception is of beings without rendering that fact unintelligible in principle. I argue that what the chapter says about the way perception is (and is not) a kind of alteration, and about the way it is (and is not) like by like, is as though designed to secure it that knowledge of beings is a fact that has causes.