As the title indicates, this book concerns the Mind–World relation in Aristotle's De anima, a fundamental topic transversely calling into question Aristotelian cognitive psychology, epistemology and ontology. The basic question K. addresses is: what is it that makes the Mind able to know the World? The attempt to account for this fact – that our Mind is able to know the World – is a book-length exploration on the very essence of perception and intelligence, the two basic cognitive capacities of our psuchē. The word ‘psuchē’ is left untranslated because the Aristotelian ‘psuchē’ denotes life as an activity, which is inadequately captured by the usual term ‘soul’. More generally, K. allows himself linguistically relaxed re-descriptions of Aristotle's theories and arguments, since his approach to texts is more oriented to deep conceptual understanding than worried by philological issues. However, such a choice does not undermine the accuracy of his analysis.

The answer to the question is anticipated in the introduction: it is by being in some sense the World – as explicitly stated in De an. 3.8.431b21 – that our psuchē is able to know the World; the passage referred to draws the essential moral of the doctrines on the ‘what-it-is’ of perception and intelligence previously exposed in the De anima. The original proposal of the book is to give a particular reading to the ‘sense’ or ‘way’ in which psuchē is the World itself and so is able to know it by being it. Provided that the question addressed, though central, is specific and orthogonal to the typical issues discussed in the relevant literature on the De anima, K.'s engagement with that literature is partial and not very systematic, but – as said – it is such with reason.

The book has a clear structure, with three Parts (‘Questions’, ‘Angles’ and ‘Proposals’), each of which is internally well-articulated into chapters according to a successfully conceived, rational and argumentative progression. Part 1, ‘Questions’, explains that, and in what terms, the question addressed is Aristotle's question, and also makes it clear that Aristotle wants to preserve – albeit only in a qualified way – two principles assumed by his predecessors: that cognition is a ‘like-by-like’ relation; and that it is a sort of alteration. In order for cognition to have some objective purport, it cannot be just a like-by-like alteration; otherwise the subject would be changed only accidentally, by contingent environmental circumstances and bodily conditions, as in a ‘Protagorean’ world where judgement is arbitrary and unstable. Instead – starting from perceptual cognition – cognitive success is guaranteed by cognition being a formal assimilation in which the subject is altered in one way, but unaltered in another, affected by the like in one way (same genus: e.g. colour-to-eye), but by the unlike in another (e.g. a given colour-to-a-transparent eye). Perceptual sense is able to remain the same even when occupying different states, since it consists in a ratio (logos: ‘a proportion’, ‘a mean’) able to receive perceptual forms/properties without being disrupted thereby. So far, this is an accurate but not a very original reconstruction of Aristotle's perceptual theory.

It is especially from Part 2, ‘Angles’, onwards that the constructive proposal is articulated. K. reads sensibility and intelligence as measures of the respective objects; the key notion of measure (metron) makes cognitive powers akin to their objects (measure and measured fall under the same genus), and it makes them the principles of the cognition of the respective objects insofar as measures are ‘“forms of the forms” of the objects they measure’ (p. 85). Perception is a qualitative measure, as it is a meson – between two opposites as limits of the range within a given genus: for example, black and white as limits of the genus [colour], with the other colours covering the intermediate spectrum – by which qualitative properties are ‘measured’, using the meson as a standard. In particular, a colour will be dark if it lies between the meson and the black, light if it is between the meson and the white. This entails that it is our sensibility – which is the form of the sensibles by being the measure of them – that determines whether a colour is dark or light, as measures are in a sense conceptually prior to what is measured.

Though well-argued, this proposal faces some problems. First, why does Aristotle only rarely characterise perception and intelligence as measures if this were the main sense in which cognitive powers are ‘forms’ of the cognisable forms? Second, it is true that the ‘mean’ our sense consists of determines whether a given sensible form is nearer to one end of a spectrum (to black = dark) or to the other (to white = light), but for Aristotle such a mean is by nature ‘wisely’ recruited as an internal mechanism in order to detect an objective equidistance from the opposite limits: each colour is really a given proportion between black and white, and a dark colour is really a mixture made out of more black than white. So, our internal mean tracks a mind-independent mean, besides being a standard for tracking other mind-independent degrees within the genus [colour]. Moreover, it is a pity that K. does not treat the perception of common sensibles, since perceivable forms like, say, a given shape are even more evidently independent from our sensibility; concerning them, it becomes even more ambiguous to say that ‘the senses are essential points of reference vis-a-vis the qualities known by their means’ (p. 96). More generally, entering into the debate about Aristotelian perception and the sense in which perceiving is receiving the form and ‘becoming’ it (literally or ‘spiritually’ or in any other way) would have been relevant for grounding a substantial account of perception being able to know the sensible world by somehow being that world.

Part 3, ‘Proposals’, after still dwelling on sensibility as a ratio and as a measure, turns finally to intelligence (nous). Unlike perception, which ‘is’ the sensible world by being a ratio/meson, intelligence ‘is’ the known world by being ‘simple’ and ‘unmixed’, just as its objects, when cognised, are simple and unmixed. In order to account for this, K. limits his analysis to nous as capable of a (non-synthetic) grasp of indivisible essences. He starts by interpreting the view that understanding is identical with its object, at least for objects without matter: as soon as nous grasps such an essence it just becomes it. The issue is quite complex, but the overall impression is that K.'s reading goes too far when holding that ‘intelligibility is a creature of intelligence’ (p. 22) and even that ‘everything intelligible is also intelligent’ (p. 131): the latter is an undesired consequence, an aporia (De an. 3.4) Aristotle clearly wants to avoid. It is true that essences are ‘separated’ from matter only by the mind and, qua so separated, they are related to an intellect (not a scandalous result); but this does not mean that they are intelligent. Besides the fact that species as essences of living beings are causally relevant in generation and are an objective part of the metaphysical arrangement of Nature quite independently of our minds, it is hard to see how the essence of [tree] or of any other natural kind, or even the abstract content of a geometrical theorem could be not only always-grasped-by-an-intellect (qua separated) but also intelligent on their own. While providing a reading of the relation between intelligence and its objects, K. misses an opportunity in opting to disregard De an. 3.5 and to keep silent about the enigmatic relation between ‘passive’ and ‘active’ intellect.

It is impossible to do justice to the richness of this proposal in a short space such as this. In any case, this book is likely to become a point of reference – perhaps a polemical one – for those who choose to focus their research on the topic with which it deals.