Whereas scholars often look to De Anima 2.5 to support one or another understanding of the sense in which perception, for Aristotle, qualifies as an alteration and qualitative assimilation to the sense-object, I ask the more basic question of what the chapter is meant to establish or accomplish with respect to the question whether perception is an alteration. I argue that the chapter does not presuppose or legitimate the view that perception is an alteration where it is thought to, and (...) that it is meant rather to challenge that view, most importantly, by putting its argumentative weight behind a different model of perception, leading to a kind of antinomy. What stands in the way of understanding perception as an alteration (and assimilation to the sense-object), in this chapter, is ultimately the lack of an account of perceiving a quality as having that quality. (shrink)