BMCR 2022.08.20

Mind and world in Aristotle’s De Anima

, Mind and world in Aristotle's De Anima. Cambridge; New York: Cambridge University Press, 2022. Pp. xii, 181. ISBN 9781108832915 $99.99.


The book discusses Aristotle’s account of why it is part of the nature of human perception and intellect to get us in touch with what exists. It consists of three parts (‘Questions’, ‘Angles’, and ‘Proposals’), of two or three chapters each, plus an Introduction and a Conclusion. It is clearly written and well sign-posted. The reader always knows what is happening and why.

Kelsey’s study is propelled by the question of why knowledge, both the perceptual and the intellectual kind, naturally belongs to the human soul. Getting clear on this question is the main focus of Chapter 1, ‘Objectives’. The short answer Aristotle gives to this question is that both sensibility, the term Kelsey prefers to ‘perception’, and intelligence [nous, noêsis] are forms of their objects. Sensibility is the form of perceptible objects, intelligence of intelligible ones. But this is obscure. The rest of the book is dedicated to making sense of this answer.

Chapter 2, ‘Problems’, argues that Aristotle’s theory of soul must explain how things appear as they actually are. Chapter 3, ‘Solutions’, turns to De Anima II.5, which Kelsey interprets as being about the ‘grammar’ of perceiving. The chapter argues that active sensibility is not a corruption or a preservation, but simply does its own work, which is to be affected and be made like the perceptible forms. In other words, perceiving is just what the sense-faculty is for, and perceiving neither worsens nor improves our perceptual capacity. (Contrast this with intelligence, which is preserved or even improved by thinking.) All this is necessary, argues Kelsey, to explain successful perceiving.

Part 2 moves on to the question of how sensibility and intelligence naturally allow us to know. Chapter 4, ‘Affinities’, tackles the issue indirectly by discussing several passages in which Aristotle discusses similarity or commonality. This is the ancient idea, discussed by Aristotle and Theophrastus, that perceiving, thinking, and many other phenomena occur ‘like by like’, i.e. because of similarity in subject and object. Kelsey argues that many phenomena (friendship, nutrition, movement, and affection) occur in this way, though with qualifications. Things interact, for the most part, because of their similar natures. This is important, Kelsey argues, because it helps us understand how the object and subject can have the same form. Chapter 5, ‘Measures’, begins to specify the way in which sensibility and intelligence are forms of their objects by arguing that measures are conceptually prior to their objects. So, for example, the meter is conceptually prior not to length, but to the length 3 meters. This is relevant because Aristotle extends the notion of measure to include qualities, such as perceptible qualities. Chapter 5 concludes with the suggestion that, since perceptible qualities exist on a spectrum, with a midpoint, sensibility itself determines where that division is drawn.

Parts 1 and 2 are mainly preparatory for the real action in Part 3 plus the Conclusion. Chapter 6, discusses sensibility along with perceptible objects, specifically the special or proprietary objects of each sense (see p. 123). Chapters 7 and 8 then turn to ‘intelligibility’ and ‘intelligence’, respectively. I begin with intelligence before returning to discuss sensibility.

When discussing intelligence and intelligibility, Kelsey reasonably focuses his discussion on cognizing essences. In Chapter 7, he argues as follows. Essences have no matter, but things in nature do. That is, nothing truly exists without matter. So essences exist only when and insofar as they are isolated from matter. Now, it is intelligence that does this isolating. Therefore, intelligence is the form of intelligible objects in that, in doing its own work, namely stripping away the matter from essences, it makes those objects intelligible. This, according to Kelsey, is how intelligence ‘measures’ its objects: by separating them from everything extraneous.

I have my questions about and quibbles with some of the book’s claims, a few of which I will mention below. But my main worry is that in several instances the book’s proposals are difficult to assess, at least for someone not intimately familiar with the relevant texts and topics. I often found myself asking just what passage in Aristotle is being examined. Similarly, I was often unsure just what evidence supports the book’s interpretations and whether these interpretations are widespread or novel. Also, it was often unclear to me what evidence might be given for alternative readings and why it is not decisive. More detailed exegesis of key passages would have been helpful to convince the reader, as would more direct engagement with secondary literature.

For example, regarding the claim that nothing is without matter except when and insofar as it is being understood, Kelsey buttresses this by means of the idea that one thinks about intelligibles by means of images. (Kelsey says ‘sensory images’ (p. 136).) Both the scope of this claim and the meaning of ‘images’ (phantasmata) are controversial, but neither controversy is mentioned. I was unsure whether Aristotle truly holds the view that everything is naturally found together with matter, which can be stripped away only by intelligence. We might also ask where Aristotle’s god, which is pure form, figures in the picture.

There is also the claim that everything which is being understood is itself intelligent, which Kelsey recognizes as controversial (p. 136). Here, his bold suggestion is that an essence removed from its matter just is the understanding of that essence, so that essences only exist as such in the intellect. The activity of stripping away matter not only makes essences intelligible, but also (so Kelsey argues) makes the essence intelligent. This is because when the intellect recognizes an essence, what it recognizes is a product of its own making. The essence, as something only produced by abstracting away anything extraneous, is itself an understanding. Thus, understanding essences is understanding of understanding. However, it is not clear to me why we cannot distinguish the act of understanding the essence and the essence itself. Kelsey argues that these are the same in being since, if they were not, the object being understood would be ‘mixed’, meaning it would be distinguished from the understanding. This requires there to be no daylight at all between understanding and its object. However, there seems to be a difference, at least between the activity of stripping away a thing’s matter and the product of that activity, the remaining matter-free essence. Perhaps a specialist on this topic will know what passages plausibly commit Aristotle to this strong idealist reading about essences and why they do so. But for my part, I was not convinced that this is Aristotle’s view.

Returning now to sensibility and its objects, colors are the special objects of vision and serve as Kelsey’s (and Aristotle’s) principal examples. Being a dark or light color is in relation to the fixed standard, the ratio that constitutes sensibility itself (120). Now, ‘ratio’ has become the standard English translation for logos in most of De Anima II.12. But Kelsey goes further and uses earlier passages in the DA as evidence that the senses are a kind of ratio, passages in which logos is not typically translated or interpreted as ratio. Kelsey may be right, but we might question whether Aristotle takes logos to have the same sense in all these passages, still more whether it always has the sense of ‘ratio’.

Still, this is fairly harmless, as it is clear that sensibility’s being a ratio is key to Aristotle’s account of its activity of perceiving. But I would have been interested to see why these other passages should be interpreted in terms of a ratio and what the consequences of this would be. I would also have been interested to see what this ratio is of for the particular senses. Kelsey strives to show that the pupil, the sense organ for sight, need not be ratio of light and dark colors (p. 111). But he does think each sense is a ratio (p. 112), though a ratio of what, he does not say. As I mentioned above, Kelsey’s main claim about sensibility is that it determines certain properties of its objects. In Chapter 6, Kelsey argues that each sense determines the midpoint of the spectrum in question. The sense organ for touch, for example, is a mean point in temperature, such that cold temperatures are cold because “being cold (period) just is being cold (as compared with the organ of touch)” (p. 115).

But even if we accept this, how does touch distinguish two hot temperatures? The most Kelsey’s account can provide in terms of defining what specific object is perceived is that it is on one side or the other of the midpoint: it is hot and not cold, light and not dark, etc. As far as I can see, it cannot account for why we see yellow instead of white, or feel something to be very hot rather than a little hot. This is not in itself a problem. And I think that Kelsey takes sensibility only to determine whether a temperature is hot or cold and not whether it is very hot or somewhat less hot (see the book’s Conclusion). Moreover, this attenuated subjectivism about sensibility is arguably more plausible than a full-on version. But the reader is left without an explanation for most of the perceptual facts.

Another worry involves other animals. Kelsey’s focus is on human sensibility, so his view is that sensible objects are partially determined by human sensibility. Now, Aristotle takes perception to determine what it is to be an animal. And except for incomplete or mutilated animals, all animals have all five senses.[1] Why, then, should we privilege human sensibility as definitory of sensible objects? Kelsey signals on p. 118 that he takes Aristotle to hold that every species has the same range of perceptibles, which would obviate the problem. But Aristotle is aware at least that different animals have better or worse perceptual abilities, so it is questionable he would accept this view, which is anyhow false.

Finally, I should say something about the subjectivism of Kelsey’s proposal. A natural reading of Aristotle’s theory of perceptible objects is realist. DA II.12, which Kelsey discusses in Chapter 6, claims that the senses receive the forms of perceptible objects. Nothing here suggests that the senses themselves are responsible for determining anything about the nature of these forms. On the contrary, the senses take on the form without the matter. One of Kelsey’s main pieces of evidence for attenuated subjectivism, Meteorology 4.4, 382a11-21, is brought in to argue that being absolutely hard or soft, two special objects of touch, just is to be hard or soft with respect to touch. But the passage, it seems to me, can be interpreted as saying nothing more than that we determine (ὡρίκαμεν) what already is hard and soft by touch, using it as a mean, not that we define the hard soft by means of our sense of touch. Kelsey translates ‘we have defined’ (p. 117). The mean that is the sense is the measuring stick we use to determine what is hot and cold, hard and soft, etc. But the measuring stick need not define the thing measured, except in the superficial sense that a meterstick measures things in meters and a yardstick yards. Here too, I found the evidence laid out insufficient to establish the claims.

Nearly all of Aristotle is hard. But the ideas and texts at the heart of this book are some of the hard hards. I learned much reading it. This book is a worthy addition to the growing literature on Aristotle’s De Anima.


[1] De Anima III.1, 425a9-11.