Although the core idea of this book goes back to an article from 2008 (‘Aristotle's Psychological Theory’, Proceedings of the Boston Area Colloquium in Ancient Philosophy 24, 1–29) in which C. offers a novel interpretation of Aristotle's hylomorphic account of the affections of the soul, the book strikes the reader as an example of how a line of interpretation can be developed into a compelling reading at the hands of a perspicacious scholar.

Chapters 1 and 3–6 focus on Aristotle's ‘simple theory’ of the psychological phenomena, according to which emotions (such as anger and fear), desire, perception, imagination and some aspects of human thought (practical thought, in particular), considered as ‘passions common to soul and body’, are all inextricably psycho-physical. In Aristotle's account such psychological activities are essentially enmattered in the particular sense that they are not decomposable into two separate components as one being purely psychological and the other purely physical. The inseparability of the psychological and the physical is not only in thought. According to C. there exists no possible way of defining any of these two without explicit reference to the other. In other words, whatever exists as physical or psychological in the composition of such activities as emotions, desire, perception etc. only exists as psycho-physical. It is in this light that in Chapter 1 C. discusses at length, as the basic model of his inextricabilist interpretation, Aristotle's remarks about ‘anger’ and ‘fear’ in De anima A.1. Aristotle thinks that, unlike the figures of geometry, these affections of the soul are ‘inseparable from the physical matter of the living beings’. Anger, for instance, is a certain type of desire for revenge, but it is also a certain type of process of a body, which consists in the boiling of the blood around the heart. C. diligently demonstrates that in Aristotle's account of anger the psychological aspect (i.e. the desire for revenge) is inseparable in definition from the physical process involved, and vice versa. The desire involved in anger is of a physical type, and the relevant physical process is of a psychological type. More precisely: the former exists only as a-boiling-of-the-blood-type-of-desire-for-revenge and the former only as a desire-for-revenge-type-of-the-boiling-of-the-blood. Chapters 3–6 discuss how this basic inextricabilist model is to be extended to desire, perception, imagination, memory and to practical thought. After a meticulous analysis of each of the five senses in Chapters 4 and 5, the first half of Chapter 6 discusses the case of the common sensibles. C.'s analysis (in the rest of Chapter 6) of ‘practical intellect’ as being inextricably enmattered will be of great interest to some readers. He argues that ‘practical intellect’ is to be ‘rational desire’ if it is to result in bodily action. C. boldly faces (in Chapter 6.7) the issue around ‘thinking’ (noein) that Aristotle believes does not involve a body as desire or perception does. C. acknowledges that noûs will be an exception to his inextricabilist interpretation although this does not change, according to him, the fact that human thinking is essentially the thinking of an inextricably psycho-physical soul and is never pure as divine thinking would be.

C. claims that Aristotle's viewpoint, in this inextricabilist interpretation, dissolves the Cartesian mind–body problem simply because it does not take its start from the most fundamental assumptions of Cartesianism. The Cartesian mind–body problem consists in the inconceivability of the emergence of the psychological component of conscious experience out of its bodily component, if these two are to be defined purely, that is, without any essential refence to each other. C. argues, throughout the book and at every stage of the development of his argument, that his inextricabilist interpretation spares Aristotle from the frailties of some of his most eminent contemporary post-Cartesian readings, such as functionalism, non-reductionist materialism and ‘spiritualism’. The latter two are particularly at the centre of C.'s attention, as they cover most of the literature on Aristotle's psychology. Both of these approaches are committed, and hence led astray by, Cartesian assumptions. In the non-reductionist interpretation Aristotle engages directly with the Cartesian mind–body problem since, for these interpreters, in every psychological activity there is a particular physical event that underlies the subject's psychological awareness and which is of the same general type as might occur in non-conscious objects. The physical is, consequently, definable without any essential refence to the psychological feature that it underlies, which, in turn, is equally non-reducible to its underlying physical event and hence can be defined in purely psychological terms. According to the spiritualists on the other hand, Aristotle takes the matter of the living organisms as being primitively endowed with capacities for psychological activities. Aristotle would, in this reading, reject that there is a distinct particular physical event underlying the psychological: all that there is to the relevant phenomena would be purely psychological. Since both of these readings rely on a purity assumption about the physical and/or the psychological, they are somehow entangled in the Cartesian paradigm and within its problems; whereas, in the inextricabilist interpretation suggested by C., Aristotle emerges as a robust alternative in philosophy of mind.

In Chapter 2 C. argues that Aristotle's ‘simple theory’ of psychological phenomena reflects, in fact, a more general account of the form and matter of natural objects as it is articulated in Physics B and Metaphysics Z and H. According to this ‘impure form’ account, as C. calls it, the forms of natural objects will refer explicitly to some of their material features, and, consequently, such objects will be defined in terms of enmattered forms. To take the example of snub noses, their ‘snubness’ is not a simple geometrical concavity, but it is rather a nasal way of being concave. Forms of natural objects are therefore inextricable from their matter. The same is true for their matter. The matter of natural objects is inextricably informed: the matter of a corpse is not the same matter as it was when the body was alive. Matter in natural organisms can only be defined in a goal-directed, that is, in a form-dependent way. This ‘impurist’ interpretation of form and matter in natural objects parallels Aristotle's account of anger, desire etc. as inextricably psycho-physical phenomena. (Scholarly readers will enjoy discovering how this perspective allows C. to conceive, in Chapter 7, a way out from ‘Ackrill's problem’.) Moreover, in comparison to its alternatives, the ‘impure form’ interpretation yields, according to C., a more subtle and coherent explanation of Aristotle's point, in Physics B, about the identity of formal cause with the efficient and the final causes. The form has to be inextricably emattered to play the causal role it is assigned in the coming-to-be of natural embodied objects.

According to the overall and radically non-Cartesian picture that comes out from C.'s inextricabilist account of Aristotle's philosophy of mind and metaphysics of form and matter in living beings, the subject of conscious experience and of all bodily processes is an inextricably psycho-physical subject, whence the title of the book: The Undivided Self.

In the last chapter (Chapter 8) C. addresses the question whether the Aristotelian viewpoint, which takes the inextricably psycho-physical processes as the basis, is incompatible with the modern view of the physical, which accounts for all physical change in terms of universal laws and explains the psychological as being grounded – in some way – in the physical. C. engages with this question from different angles but the gist of his answer consists in saying that Aristotle's position allows to view the physical in its purely physical features only if this is understood as a type of ‘abstraction’ from the inextricably psycho-physical, which is also the metaphysically basic starting point for all legitimate explanation of natural reality: snubness can be seen, after all, as geometrical concavity, although it only exists as nasal-concavity.

C. offers, in the introduction, different paths of reading his book through its chapters, which makes it all the more appealing to specialists, and to non-specialists as well, in philosophy of mind and ancient philosophy. The range of issues addressed in the volume and its unflagging engagement with these issues will be a source of inspiration to its readers as an example of intellectual courage.