Structure and the Metaphysics of Mind offers a significant contribution to the current debate in the metaphysics of the mind. Jaworski presents an original version of hylomorphism (HM), which allows us to approach several central issues in analytic philosophy in a new way, such as the problem of composition, the legitimacy of mechanistic explanations in biology, and the mind-body problem. HM deserves serious consideration amongst other non-reductive accounts since it provides new compelling solutions to the problem of restricted composition, emergence, and downward causation. Readers will have much to benefit from reading this thought-provoking book. Even if some might think that the promise of a solution to the mind-body problem is ultimately left unfulfilled, its value is that it points at a new promising direction.

Jaworski starts building a metaphysics for HM, a naturalistic and non-reductive view that rejects both physicalism and some tenets of emergentism, and assumes hylomorphic structure as basic ontological and explanatory principle. For Jaworski structure matters (it is an irreducible ontological principle that accounts for what things essentially are), structure makes a difference (it is an irreducible explanatory principle that accounts for the powers things possess), structure counts (it serves as principle of individuation and explains the unity and persistence of complex things), and structure minds (it allows to locate mental phenomena within the natural world).

In chapters 2–4 Jaworski defends a substance-attribute ontology for which properties are sparse, and they are tropes: only properties that empower individuals to enter into causal relations exist; thus, higher-order predicates do not express genuine properties: there are no determinable properties (such as redness), only determinable predicates (such as ‘is red’), and the only real properties are fully determinate.

Moreover, Jaworski argues for a power-trope metaphysics (contra a categorical-universal one): ‘structures are powers to organize or configure things – powers that structured wholes are essentially engaged in manifesting. […] These particular configurings – yours and mine – are particularized properties or tropes.’ (4, my emphasis). For Jaworski's identity theory of powers (i) ‘dispositional’ and ‘categorical’ are different vocabularies rather than kinds of properties; (ii) properties are powers essentially directed toward their manifestations, which (iii) happen when conjoined with disposition partners under the right circumstances; and (iv) powers are individuated by their manifestation complexes, i.e. possible ways in which they can manifest themselves in conjunction with disposition partners.

Chapters 6–8 are devoted to mereology: the only real parts of individuals are biofunctional parts individuated by activity making structures, namely ‘coordinated manifestations of the powers of their parts’ (155). From this follows the embodiment thesis: all powers of structured individuals are essentially embodied in their parts (n.b. psychological activities included). Similarly, composition is restricted to structured emergent individuals who are essentially engaged in the activity of configuring the materials that compose them. Hylomorphic individuals’ properties are (i) first-order (as opposed to higher-order), (ii) not epiphenomenal (since they are powers), and (iii) embodied in and necessitated by the structure and the causal powers of their parts. On this note, Jaworski's proposal provides metaphysical ground to mechanistic explanations in biology and neuroscience (e.g. by Bechtel and Craver) based on the assumption that organization is not inherent in the parts, in line with HM's claim that ‘structure make a serious ontological demand’ (3).

Chapters 9 defends strong supervenience (based on the embodiment thesis) and Chapter 10 rejects lower-level determination (as incompatible with the ontological primacy of structure), from which follows Jaworski's cogent treatment of the problem of emergence and of downward causation. They both look now more tameable in the light of HM.

The rest of the book is devoted to the worry that HM might ultimately be just a ‘polite form of materialism’, and nine related objections. For reasons of space I will only focus on one, which in my mind represents the main flaw of this otherwise compelling proposal. For Jaworski, activities such as thought are ‘composed of the structured manifestations of the powers of lower-level things, [which] are typically revealed through functional analysis’ (255). If so, goes the objection, consciousness can be understood in physical terms, making HM vulnerable to Chalmers’ conceivability argument against materialism. The argument claims that zombies (an instance of ‘P & ¬Q’) are metaphysically possible, because from their conceivability follows that truths about Qs are not a priori deducible from truths about Ps, which is at odds with a relationship of identity or necessitation between Ps and Qs. Since HM assumes that necessitation relation, says Chalmers, HM (as materialism in general) must be false.

Jaworski replies that conceivability does not entail possibility, for our concepts needn't correspond to genuine properties, and a fortiori to genuine possibilities. Moreover, HM takes relations between an individual's activities and the powers of its parts to be strong a posteriori necessities, which implies that there can be epistemically possible scenarios that correspond to no metaphysically possible worlds. If so, the argument fails.

Jaworski claims that HM solves the hard problem and the mind-body problem assuming the ontological primacy of structure. Nonetheless, HM's anti-reductionism clashes with Jaworski's take on the distinction between the mental and the physical: ‘[HM] does not treat the mental-physical distinction as canonical, but simply as an artefact of our descriptive and explanatory interests. […] whether we decide to call some of these powers or manifestations “mental” or “nonmental”, or “physical” or “nonphysical”, is orthogonal to the project of understanding what they are.’ (173–174). A requirement for HM's anti-reductionism solution to the mind-body problem and to the hard problem is arguably the ontological commitment to the existence of mental properties distinct from physical properties. But the appeal to higher-level properties is not sufficient, for mental properties wouldn't be any different from higher-level non-mental properties (e.g. chemical or biological). If so, we are not better off embracing HM than eliminativism, since for HM mental/phenomenal properties deserve no special treatment.

The burden of proof might be on the advocates of such specialness, but Jaworski grants the legitimacy of the intuition behind the hard problem: ‘I consider [the case of zombies] to be highly counterintuitive […], but I do not purport to have shown that [it] is impossible.’ (196). This book provides a very promising framework. Jaworski's proposal is a paradigmatic example of the bold and original contributions we need to tackle problems of such difficulty. This attempt is successful in defending HM in the extra-mental domain, and the fact that the promise of a solution to the mind-body problem remains unfulfilled should not be seen as a failure, but as a starting point and an indication that more work is needed in the same direction.