If the argument of this book has been on the right track, Aristotle affords, within his study of the first principles of animal life, pride of place to the classification of the primary perceptual acts as complete passive activities. This is not a claim about the nature of sense-data or about the sensing of mere qualities. It is, rather, a claim about perception in a rudimentary but robust sense of directly accessing the external bearers of modal-specific qualities. These rudimentary perceptual acts are cases of κρίνειν; they – and only they – reliably identify those qualities as distinct from any other perceptual feature that the objects could have. It is this explanatorily primary layer of perceptual experience that Aristotle wishes to analyse under the concept of complete passive activities.

His claim is not just that these acts involve passive processes. He, to be sure, never intended to deny that they do. However, when he identifies perception as a kind of being affected, he means what he says. To appreciate this classification, we must shed some of our deeply ingrained intuitions about ‘passivity’ and ‘activity’. The idea that there are complete activities that are essentially passive may sound paradoxical to us, and it is certainly not to be taken for granted. However, Aristotle believes that we cannot move forward in understanding what perception is without seeing how complete passive activities are possible. This is the case because perceiving consists in being assimilated to something else, but without losing causal contact with it, as is the case with a mere appearance. Continued perceiving, and thus any perceiving whatsoever, is, in Aristotle’s view, possible only if perceivers preserve their unlikeness vis-à-vis the perceived objects acting on them. The qualities they receive must not become their own; they ought to remain qualities of the perceived objects out in the world. Perceiving, to put it bluntly, is receiving forms without the matter.

This admittedly abstract analysis encapsulates Aristotle’s novel ontology of perception, which underlies his inquiry into the first principles thereof. Perception is essentially a way of relating to external reality. But it is also irreducibly qualitative. Although the qualities of perceived objects must not become qualities of the perceiver herself, they do come to be present in her. And they come to be present in her in a new way that cannot simply be explained away. In contrast to contemporary defenders of qualia, however, Aristotle is not so much interested in the subjective or private character of perceptual experience – that is, in the irreducibility of ‘what it is like’ to perceive this or that. One might say that perception is, for him, objectively qualitative in the sense that the qualities constituting it remain qualities of the external objects, while coming to be present in the perceiver: perception, and only perception, is how these qualities (and so their bearers) reveal themselves in a perceiver, without anything subjective or personal interfering. It is exactly the notion of complete passive activities that, by Aristotle’s lights, successfully integrates this simultaneously relational and qualitative nature of perception.

This all implies that perception is, on Aristotle’s view, a more dynamic phenomenon than is usually acknowledged by scholars. And this has direct consequences for the much-debated question of the role of the perceptive body. It is wrong to foist onto Aristotle the assumption that either the perceiver acquires a material likeness to the perceived object (be it literal or analogical) or that perception involves no material processes whatsoever. This kind of disjunction is exactly what makes us blind to the core idea. Material processes are, no doubt, essentially involved in perception; but, if perception is not to end in failure, those processes cannot result in any standing material likeness. The resulting likeness is dynamic (it is, so to speak, established in each moment anew) and is fundamentally cognitive, or ‘phenomenal’ if you wish: it is how a quality of an outside object reveals itself. It should be clear by now that accepting ‘phenomenal’ likenesses into the picture does not mean turning Aristotle into a spiritualist. It is merely a way of acknowledging that the primary perceptual acts cannot be explained away or reduced to ordinary material processes. That is, of course, something entirely different from saying that these acts have no essential link to any material process. In fact, once we take Aristotle’s causal account of these acts seriously, we can see that he is willing to give much more of an explanation of perception than is allowed for by most existing non-reductive materialist readings.

The primary cause of perception is, for Aristotle, nothing other than the perceptive soul. But it does not play this role by being itself the proper subject of the perceptual object’s acting. That would involve the illicit assimilation of the soul to bodies, and so of the explanans to the explananda, in a way that would effectively beg the question. Nor does perception just vaguely ‘supervene’ on material processes. Rather, I argued, Aristotle conceives of the perceptive soul as the controlling factor of a very precise homeostatic mechanism. That mechanism can be approached as a refinement of the most fundamental self-preservative activity of living, but directed to an entirely new purpose – namely, receiving qualities possessed by outside objects: not devouring things, but taking them in as they are on their own. This turns perception into an essentially different kind of activity: the most rudimentary complete passive activity.

Given Aristotle’s willingness to use his analysis of perception as the starting point of his inquiry into the thinking part of the soul, we can expect that the proposed analysis of complete passive activities will also bear fruit there. However, because thought has an entirely different kind of correlative object (namely, the very essences of things) and because it is, by Aristotle’s lights, not a bodily activity, the flesh and bones of it – if that language can be retained at all – will have to be very different. Elucidating them is a task that must await another study.