In the de Anima Aristotle holds that we can perceive ordinary objects and discriminate their different features in virtue of the senses rather than the reasoning capacity. He says, for instance, that the sense of sight and the sense of taste can concern the same object, say bile, and discriminate its being yellow from its being bitter (de An. 425b1–2). However, it is not clear how he limits the scope of a single sense. The received interpretation that goes back to Thomas Aquinas and even further to Alexander of Aphrodisias consists in two claims: first, that Aristotle defines a single sense by reference to its ability to perceive the sensible properties that are proper to that sense, colour for sight, sound for hearing, and so forth, and second, that he explains perceptions of unities of these items, and differences between them by reference to a further, higher-order capacity that the senses share with each other, and which is called the ‘common sense’. But I argue that this interpretation is problematic. It is problematic because, among other things, it judges Aristotle incapable of explaining how we can perceive contrary sensible properties such as white and black at a time. On the alternative interpretation that I propose, Aristotle defines the sense by reference to its ability to discern the differences between its proper items. That is why, I argue, he refers to each single sense as a capacity for discriminating (to kritikon), which implies that he regards discrimination as the basic function of each sense. The aim of the paper is thus to show that Aristotle’s theory of sense perception is basically a theory of perceptual discrimination.