Since Aristotle, philosophers of differing approaches have assigned epistemic and semantic functions to mental entities in virtue of their representing extra-mental things. However, since the individuation of those entities is considered to be distinct from any representing function they may have, then regardless of whether the mental is reduced to the physical or not, that representative function cannot individuate such entities and what are known and referred to primarily are the individuated representations themselves, while the represented entities, things in extra-mental reality, are only known and referred to secondarily, through a context of interpretation. Against such considerations John O’Callaghan's account of St. Thomas's view identifies a distinction between the instituted sign relations of words to passiones animae and words to res extra animam as opposed to the natural likenesses (similitudines) relation of passiones animae to res extra animam and argues that the epistemic and semantic functions St. Thomas assigns to passiones animae are not representationalism so construed.

Chapter one introduces the (in)famous gobbet from Peri Hermeneias(16a3–9) that identifies the vertices of Aristotle's semantic triangle: words, passiones animae, and res extra animam. The relations between these vertices are affirmed as irreducibly different and the activity of the intellect identified as the means by which a general word can be predicated of singular things. Chapter two argues against Kretzmann's contention that Aristotle is not primarily concerned with semantics but rather wants to distinguish signs and symbols and affirm the priority of the sign relation of word to passiones animae over the symbolic relation of word to passiones animae. It also distances St. Thomas's view from those of Ammonius and Boethius. Chapter three considers the mental representationalism of Locke, Berkeley and Hume and some objections raised against them by Husserl, Frege and Wittgenstein. Chapter four outlines Fodor's revival of representationalism and chapter five Putnam's attack on representationalism. The next three chapters distinguish St. Thomas's account from three theses O’Callaghan thinks characteristic of mental representationalism: that the representation is a ‘third thing’ between mind and world (chapter six), that it is knowable introspectively independently of res extra animam(chapter seven) and that it is individuated solely by its own properties, that is, internally (chapter eight). Chapter nine concludes the book with a discussion of the social and political effects of human conceptual activity.

Two reasons distinguish passiones animae from the representations Putnam attacks. Firstly Thomas disassociates the ‘primorum’(or ‘primo’– the point is independent of the textual dispute) in the gobbet from direct and immediate and the implied ‘secondarily’ from indirect and mediate. Words are thus not related firstly, directly and immediately to passiones animae and then only secondarily, indirectly and mediately to res extra animam. Rather words are related firstly to passiones animae that are simple acts of the intellect and secondarily to passiones animae that are complex acts of the intellect. Directly and immediately a general word is related to the passio animae it signifies; indirectly and mediately a general word is related to the res extra animam it signifies. Although both relations are types of signification, the first is subordinate to the second and only necessary because of the means by which general terms signify. Only the second relates a word to a thing and it does so by means of the passio animae caused by the res extra animam because there are no general subsisting entities for such words to signify directly and immediately.

Secondly passiones animae are not ‘third things’, not knowable introspectively independently of res extra animam and not internally individuated. They are not ‘third things’ because for St. Thomas the mind thinks via conceptualisation and the ‘concepts’, which passiones animae are, are just nominalized forms of speaking about the actualization of the intellect. As for introspection, passiones animae can be so known but not independently of one's knowing a res extra animam. If a res extra animam is not being known, the intellect is not being actualised and there is no passio animae for the knower to know, let alone to represent something else. Finally, since a res extra animam efficiently and formally causes a passio animae of the same nature absolutely considered, no passio animae can exist accept as an effect of the res extra animam that efficiently and formally causes it and as such cannot be individuated solely by reference to its own properties.

None of the above however, holds for the relations of words to passiones animae or words to res extra animam. Words are something (sounds) independently of their representing function and that function is fixed by linguistic communities: the passio animae or res extra animam signified by ‘man’ can also be signified by ‘homo’, ‘anthropos’, ‘homme’, and so on.

This is an excellent book by an author committed to describing St. Thomas's thought through the resources of analytical philosophy. It ought to encourage Thomists in that project and become compulsory reading for English Dominican Province students. Let me end with three points of criticism. Firstly given that on St. Thomas's view the intelligible species is the form of the act of the intellect, then part of the difficulty in explaining his position is in accounting for how a form, whether substantial or accidental, can be that by which something either is or is by some mode, without that entailing that the form itself is simpliciter. This however is an issue of Thomas's broader metaphysics; thus the problem O’Callaghan discusses finds its context in that metaphysic to which attention could have been drawn. Secondly more could have been said about the relation of meaning to signification other than endnote 14, p. 301. Thirdly, there is no section 56 in Klima's essay on St. Thomas's semantic principles; endnote 16 on p. 301 is inaccurate.