The chapter develops the question (raised in Chapter 4) about the precise way in which soul is supposed to play the role of the primary explanans of perception. It does so by bringing out the key difficulty that Aristotle faces and by analysing the three possible answers to this difficulty. The problem is that Aristotle seems to commit himself to three jointly inconsistent tenets: (i) the perceptive soul is the primary cause of perception; (ii) perception is passive; and (iii) the perceptive soul is impassive. These claims are inconsistent if it is true that (iv) there is no way for the soul of being the primary cause of φ-ing other than being the proper subject of whatever φ-ing consists in. Two dominant ways of resolving this problem, since antiquity, consist in denying Aristotle’s commitment to either (ii) or (iii). I argue that difficulties, both exegetical and philosophical, faced by each of these strategies are insurmountable. The third possible strategy starts from denying (iv). I trace such a strategy to the medieval idea of a sensus agens and argue that although the existing medieval (and later) versions cannot stand as such, the third strategy is nevertheless the most promising one.

The chapter explores how Aristotle wants to account for perception’s essentially receptive nature. It focuses on Aristotle’s commitment to the passivity of perception, namely, the idea that perception is a certain kind of being affected (paskhein) by perceptual objects. It provides a classification and preliminary critical analysis of existing interpretations of the passivity of perception. I argue that Aristotle’s first general account of perception in An. 2.5 is systematically pre-causal in the sense that makes it impossible to directly infer from it anything specific about the respective roles of the body and the soul (against both Material and Psychic Interpretation). Furthermore, I contend that Aristotle develops a robust conception of passivity here that successfully encapsulates, on the most general level, what perception is (against Deflationary and Aporetic Interpretation). More specifically, I argue that An. 2.5 is centrally aimed at reconciling perception’s passivity and completeness (the perceiver has both seen and is seeing the same object) and that this task is motivated by the need for capturing the difference between genuine (‘continued’) perceiving and mere appearance within an assimilation model of perception.

The chapter starts by outlining the version of direct realism endorsed by Aristotle. I argue that he was committed to uncompromised realism about perceptible qualities and to the view that we immediately perceive the bearers of these qualities without any need of further synthetic acts. These features highlight the difficulty of capturing the explanantia of perception. Two notions key to that endeavour are those of mediation and discrimination. The chapter provides a novel analysis of mediation (for discrimination, see Chapter 6), arguing that, for Aristotle, media are – more or less perfect – qualitative conductors. Furthermore, the chapter addresses the existing debate about what, according to Aristotle, happens in the sense organs when we perceive. I argue that the dilemma governing this debate between spiritualism and materialism (either ‘literalist’ or ‘analogical’) is a false one. Tertium datur, and this alternative turns out to be precisely the view Aristotle embraced: perception consists of a thoroughly material process, but what this process results in must not be a standing material likeness (which would mark the end of perception because like cannot be affected by like), but a dynamic ‘phenomenal’ likeness – the presence of a quality of the perceived object which remains to be precisely a quality of that object.

The chapter provides a novel account of perceptual discrimination (krinein) in Aristotle. Against the widespread view that the most basic perceptual acts consist in noticing differences between two or more perceived qualities, I argue that discrimination is for Aristotle more like sifting, winnowing on a sieve: it consists in identifying – with an ultimate authority – the quality of an external object as distinct from any other quality of the given range that the object could have. The chapter further explores how the notion of discrimination is embedded by Aristotle within his causal assimilation model of perception. I argue that the central notion of a discriminative mean (mesotēs), introduced in An. 2.11, is intended to capture the role of the perceptive soul as the controlling factor of a homeostatic mechanism underlying perception. As such the notion lays the groundwork for resolving the apparent conflict between the passivity of perception and the impassivity of the soul (as analysed in Chapter 5). The prospect is further explored in Chapter 7. The present chapter concludes by arguing that Aristotle conceives perceptual discrimination as a holistic assessment of the external object acting on the perceiver, including those of its features which are not causally efficacious.

The chapter spells out the homeostatic model of how the soul is involved in perception introduced in Chapter 6, while addressing two main challenges for it. First, I argue that while the physiological details are not easy to tease out, there is no principal reason against Aristotle’s extension of the model from touch to other sense modalities. More importantly, I argue that we can understand the role of the perceptive soul as an extension of the model developed for the nutritive soul in An. 2.4 and based on Aristotle’s art analogy (from Phys. 2 and elsewhere). The upshot is that the basic perceptual acts are underlaid by bodily processes non-cognitively controlled by the soul. But while homeostasis is the aim of nutrition, in perception it only becomes a means for achieving something else, namely discrimination. The chapter closes by showing how the interpretation developed in this book pays off when it comes to understanding Aristotle’s two notoriously difficult concluding accounts: the account of perception as a reception of forms without the matter in An. 2.12 and the summarizing account of the cognitive soul in An. 3.8.

The chapter sheds fresh light on Aristotle’s account of perception by providing a novel analysis of the puzzles that he articulates within his discussion of the predecessors’ views, especially in An. 1. I argue that Aristotle takes the key insight of the traditional view that like is perceived by like to be expressed in the idea that the perceiver is like the perceptual object by which she is being affected. This idea seems inconsistent with the widely shared assumption that only unlike things can act upon each other. Aristotle’s predecessors were unable to resolve this tension (the notion of a generic likeness is of no help), but he believes that precisely this tension must be resolved by any successful account of what perception is. The only predecessor who at least hinted towards a resolution is Anaxagoras with his account of impassive nous (understood by Aristotle as a general account of cognition). But Anaxagoras failed to account for the causal aspects of cognition as a way of being affected by its object. Aristotle’s own account can be seen as an attempt to incorporate the true insights of both the view that in perception like is affected by like and the view that what perceives must be impassive.

The chapter provides a novel detailed analysis of one of the most discussed chapters in the Aristotelian corpus, namely An. 2.5. The central claim is that in An. 2.5 Aristotle lays down his programmatic definition of perception as a complete passive activity. He does so by classing the perceptive capacity with capacities that are already fulfilments (entelekheiai) of their subjects and by showing how this classification is compatible with perception being passive (i.e. a kind of being affected). By working out the concept of complete passive activity Aristotle fills in a conceptual gap left open elsewhere in the corpus (most strikingly in Metaphysics Θ.6), where both completeness and passivity are taken for granted but without showing how the two features can cohere. In An. 2.5, Aristotle, thus, succeeds in capturing how perception differs not only from manifestations of non-passive complete capacities (such as the art of house-building), but also from passive processes (as exhibited in the inexhaustibility of the perceptive capacity and the object-directedness of perception). His definition is programmatic in the sense that it analyses the explananda without, however, yet providing any explanantia.