Kalderon states that his aim in this book is the pursuit of the philosophy of perception through its history. He defends what he terms an ‘anti-modern conception’ of colour and colour-perception, attributing a version of this theory to Aristotle. His central theme is that the account of perception put forward by Aristotle in De Anima and elsewhere is best understood as a response to the theory advanced by Empedocles. Over a number of chapters he carefully outlines the different strands in Aristotle's overall account of perception, with a view to clarifying the notorious definition of perception as ‘the assimilation of the sensible form without the matter of the perceived object’.

Kalderon makes a good case for the view that much of Aristotle's positive theorizing about perception can be seen as part of an attempt to resolve a tension in Empedocles’ account. The Empodeclean puzzlement, as Kalderon terms it, arises from the fact that in visual experience the perceiver becomes aware of the qualities of external objects located at some distance from the subject. How is it that when the subject is situated here, their experience makes present the colour quality that is situated on the surface of a remote physical object located over there? Kalderon observes that this puzzle about perceptual experience persists to this day. (It is well articulated in Jerry Valberg's The Puzzle of Experience (1992), as he notes.) However, for Empedocles there is an added problem, insofar as he also advocates an explanatory theory according to which all perception is essentially a form of contact with the perceptual object. This leads Empedocles (and also Plato, in the Timaeus) to claim that in colour vision the eye somehow takes in, or physically ‘ingests’ material effluences emitted by the distal object. On Aristotle's contrasting view, no matter is taken in by the perceiver. The problem is then to provide an alternative theory. For Aristotle, to see the red colour of an external object is not to ingest or grasp anything material, but instead, to assimilate that object's sensible form without assimilating any matter from the object.

Kalderon devotes a number of chapters to a close examination of Aristotle's treatment of vision, and defending its internal consistency. He does a good job in spelling out Aristotle's overall position, and explaining what Aristotle means when he argues that colour is a power to move, or alter, what is transparent. There is much useful exegetical material in his elaboration of Aristotle's ideas on the nature of light and dark, on the generation of the hues, and also dealing with the primary (or special) and general objects of perception, and the distinction to be made between the physiological activity in the eye and the sensory presentation of colour to the perceptive part of the soul. Aristotle rejects the idea that light is some kind of corporeal stuff emanating from the perceptual object, in part on the mistaken empirical grounds that light could not be composed of something that could move so quickly through space. Kalderon sympathetically explains how Aristotle conceives of light as incorporeal activity. It is a state of a potentially transparent medium, a state akin to, or equivalent to, a state of illumination. Strictly speaking, states of colour do not move. Therefore ‘the colours of things are at best indirectly located, inheriting their location from the particulars in which they inhere’ (51).

While there is plenty of interesting argument in these chapters, there is an occasional repetition of claims, and the overall path of the argument is not always easy to follow. Also, in the light of Kalderon's aim of pursuing the philosophy of perception, the exposition might have benefited from the clarification of the role of Aristotle's more speculative theorizing in his attempts to construct an explanation of the nature of light, and the extent to which these could be separated from his more a priori principles about the general framework within which we should try to make sense of perception. Empedocles’ version of the ingestion model can still be rejected even if one retains the idea of light as some form of matter (understood in a broad sense as comprising wave-particles) travelling through space, and thus as contributing to a causally linked chain of events, originating in the surface colour of the distal object and resulting in some change in the perceiver's experience.

More contentious, however, are Kalderon's claims, in the final chapter, about the meaning of Aristotle's central tenet that in perception, the perceiver, or their experience, becomes ‘like’ the object of their experience, and his interpretation of Aristotle's signet-ring and wax impression analogy.

For Aristotle, a visual experience is produced as the effect of a distal object, and it becomes like that distal object, in some manner to be further explicated, by sharing its form. As is well known, there are a number of different ways of interpreting Aristotle's claim. Kalderon rejects Sorabji's view, that some quality in the sense-organ becomes literally like the sensible property; he also argues against Burnyeat's view that no material change necessarily accompanies the assimilation of the form of the distal object by the perceiver's sense-organ, when they become aware of a colour. However, as Caston and other commentators have argued, there are various plausible views that avoid such extremes. Likeness of form can be understood as something closer to ‘isomorphic with', perhaps at a higher, more abstract, level; or, we can interpret the experience as involving some kind of intentional state – with the result that the experience becomes like the sensible quality by representing it. But in either case the experience can still be understood as a state of the perceiver which is distinct from the state of the perceptual object that the experience is of, and whose effect it is. Hence one plausible way to treat Aristotle's theory is as a forerunner to modern causal theories of perception. A sensory impression can be compared to an impressed wax seal, which to some extent resembles its cause, the signet ring.

While Kalderon accepts a version of the abstract isomorphism idea, he adds a distinctive twist in ascribing to Aristotle a form of direct realism, or disjunctivism (which he terms, somewhat misleadingly, ‘perceptual realism’). Kalderon argues that, for Aristotle, the perceptual object is a ‘constituent’ of the subject's experience, referencing the work of John McDowell and other contemporary disjunctivists. When the perceiver sees the white of the sun and assimilates its chromatic form ‘the white of the sun constitutively shapes the perceiver's experience of it’ (176). In initially attempting to clarify this notion of ‘perceptual shaping’ Kalderon appeals, by way of example, to how St Paul's Cathedral constitutively shapes the London skyline by being part of the contour of that skyline. Analogously, he suggests, ‘The whiteness of the sun shapes the contours of your visual experience … simply by being present’, and in this way it becomes a constituent of your experience when you see it. Now, on a modest interpretation of these claims, the causalist could agree: if what is caused in the perception of a distal object is an inner state of the subject, the same colour quality (or form) could be instantiated by two distinct entities, the sun, and the subject's inner experience.

Kalderon, however, has in mind a stronger interpretation. In speaking of ‘the whiteness of the sun being present’ he appears to have in mind the trope that is the particularised quality of the sun being white; he argues that in seeing the colour of a distal object, the perceiver assimilates ‘that particular's chromatic form’ (all italics mine). So it seems that it is the trope, the whiteness of the sun, that is the constituent of the perceiver's experience, although the point is not made entirely clear; and the issue is further complicated by the fact that exactly how the colour appears in illusory conditions depends also upon the subject's point of view. Hence other factors can affect the way that the colour of a remote object is presented in visual awareness, and there need not be a complete match of the objective colour and the colour present in experience. In any event, the resulting account is opposed (in Kalderon's view rightly) to scientific accounts of the sensible qualities – such as colour and sound – that we are immediately aware of, according to which the sensible qualities are complexes of primary qualities belonging to distal structures, which cause distinct inner sensory states. Kalderon argues that ‘Aristotle has in mind a non-causal sense of impression’ (173), and claims that only something like the presentational conception of experience that he attributes to Aristotle can account for the objectivity of perceptual content.

It is not obvious that anything like this direct realist analysis is set out unequivocally in Aristotle's writings. Why then does Kalderon attribute it to Aristotle? One central argument adduced by Kalderon is based upon the way that we individuate perceptual experiences. He begins by focusing on the Aristotle's signet-ring and wax seal analogy. According to Kalderon, the point of the analogy is to illustrate the way in which experiences are more than the mere causal effects of objects. A seal carries an authority deriving from its legitimate source; it has to be produced in the appropriate manner, by the legitimate possessor of the signet-ring. Analogously, sensory impressions are individuated by their legitimate sources, meaning that they are individuated by their objects. Kalderon argues that if sensory impressions are understood as merely the effects of causal shaping, we cannot explain the individuating relation between impression and object, since ‘cause and effect are contingently connected’ (175). A perceptual impression of Castor may be subjectively similar to an impression of Pollux, but they are to be distinguished by their different perceptual objects. Kalderon concludes that ‘… in being individuated by their [perceptual] objects, these objects constitutively shape our sensory impressions of them’.

One difficulty for this line of argument is that it does not explain how the perceptual objects themselves are individuated in the first place. On what basis can it be determined whether Helen is seeing Castor or Pollux? The only principled, non-circular, means whereby we can identify the object of a given perceptual experience is by reference to the causal route that tracks back in perception to the perceptual object. It is true – as Kalderon notes – that the perceptual object is not identified simply by virtue of being a mere cause of a sensory impression. Rather, it is determined by being the specific cause that brings about the impression in the appropriate way. It is causally produced in the manner distinctive of distance perception. There is no circularity here, for as Aristotle notes in De Sensu, there is an internal connection between the perception of remote objects and the ability to act for the purposes of self-preservation: the relevant sensory processes are those that enable creatures to move around and act upon distant objects so as to obtain nourishment and avoid harm.

It can therefore be argued that in a perceptual situation there is a causal link between two distinct events, the distal object and the inner experience, just as in the wax case there is a causal link between the signet-ring and resulting isomorphic wax seal. There is no conflict here with Kalderon's claims about individuation. Metaphysically speaking, there are causal facts about which kinds of things or events are related to other, distinct, kinds of things or events in perception; at the level of logic and language there are ways we make identifying references to, and describe, those same things or events which, because of our descriptions and identifications, and because of our systems of classification, can make for close conceptual connections between them. But these two levels are perfectly compatible with each other. So the fact that in this formal sense the perceptual object is a constituent of the subject's experience does not preclude a causal interpretation of Aristotle's account of perception.

By appealing to his idea of constitutive shaping Kalderon attempts to explicate a more substantive notion of what it is for an object to be a constituent of an experience. He argues (on behalf of his version of Aristotle's theory) that, for example, ‘Sensory experience is an encounter with … its primary objects [such as colours]’, ‘In sensory consciousness, we simply confront the primary object of the given modality .... ’, and ‘… the sun's whiteness … shapes the contours of your visual consciousness …’. His idea seems to be that the actual character of the subject's visual experience – the ‘what it is like’ aspect – derives from properties of the object actually seen.

Kalderon elaborates and defends this account in some detail. But there are two major problems with it. The first is that such phenomenologically based attempts to explain what it is for an external object to be a constituent of one's experience are circular – they already presuppose a direct realist view of perception, by assuming that a perceptual encounter somehow enables the subject to become immediately aware of the sensible properties of external objects. The appeal to the notion of what is ‘present’, or what we ‘encounter’ presupposes the very conception of perceptual experience that we are trying to explain (Kalderon is not alone among contemporary theorists in appealing to these kinds of question-begging explanations). So we have done nothing to resolve the initial Empodeclean puzzle: we still lack an explanation of how it is that the experience can connect a perceiver located at one position to an external object situated at a different place. How does the experience reach out to and include the perceptual object? The central difficulty remains.

The second problem is that even if we could explain what it is for an external object to be present in sensory consciousness, and present as a constituent of the experience in something more than the merely formal sense, it is not clear why we should prefer such an account to the more straightforward causal view that many of Aristotle's remarks about the nature of perception in De Anima and elsewhere point towards.

For these reasons it is not clear to me that Kalderon succeeds in integrating Aristotle's proto-scientific ideas about the nature of perception with an adequate philosophical analysis of the concept. There is certainly a good deal of interesting analysis presented in this book of Aristotle's ideas about light and colour, and about how they relate to those of his predecessors. Yet it is arguable that much of the discussion of the detailed nature of Aristotle's account of transparency, and of colour, and light and dark, is independent of exactly what is meant by Aristotle's claims about the assimilation of form without matter. Nevertheless, those who are unsympathetic to the causal theory of perception will find plenty to agree with here, and Kalderon has done a useful service to his contemporaries in showing how his writings about perception can be interpreted in a manner that locates Aristotle in the direct realist camp.