To some it may seem that there could be no need for another study of Aquinas's Summa theologiae (ST), and more particularly its so-called "Treatise on Human Nature." The Questions that make up this "Treatise" are, after all, among the most widely read in the best known work of the most prominent philosopher of the Middle Ages. And didn't Anthony Kenny publish a philosophical commentary on this very same treatise less than a decade ago? Yet Pasnau's book is, as the book cover proclaims, a "major new study" of Aquinas that will undoubtedly be read widely and discussed critically for a long time to come. It is major in scope, inasmuch as Pasnau (unlike Kenny) analyzes the questions on human nature in light of the whole of Aquinas's corpus. Indeed he often goes well beyond the subject matter in the Questions themselves to give crucial background to the topics embedded in the articles under consideration. Then, too, this is a thoroughly philosophical study which places Aquinas's thought front and center and analyzes its coherence and adequacy not only as a medieval product, but as a possible philosophical contender today. In these ways Pasnau's book belongs to a new breed of scholarly works on medieval philosophy. One of the potential merits of this new kind of scholarship is that it seeks to address at once the novice, the non-specialist, and the specialist. Pasnau succeeds remarkably well in achieving this aim.
From the beginning Pasnau alerts his reader that he has "some novel and perhaps surprising things to say about Thomas Aquinas" (1). Part of his methodological novelty is to suggest that all of Aquinas's works are like "rough drafts" on the way to Aquinas's ideal philosophy (6); the ST is just the closest to that ideal (428, n. 17). Dissatisfied by how much consensus there seems to be in the secondary literature on Aquinas, Pasnau begins already in the Introduction to make waves with some provocative remarks. Aquinas's philosophy is, he says, "Aristotelian in the way his theology is Christian" (2-3), notwithstanding how well established is the formative Neo-Platonic influence in Aquinas's synthesis. In facing the inevitable question why a philosopher today would devote so much attention to a work that is really a medieval theological textbook, Pasnau makes the interesting suggestion that philosophy today actually has more in common with medieval theology than with medieval philosophy as practised by Arts masters (11). Also interesting but debatable is his presumption that medieval theologians and philosophers regarded human nature as "their central subject matter" (14). That fits well with Pasnau's interest and even with the layout of the ST (the second part, on human actions, is by far the largest), yet Aquinas holds that theology is primarily about God and is concerned with creatures only as ordered to God as their beginning and end (ST I.1.7).
The study is divided into three parts, the first dealing with the nature of the soul and its union with the body (Questions 75 and 76), the second with the soul's capacities, especially sensation, desire, freedom, and voluntary action (Questions 77-83), and the third with intellectual cognition, self-knowledge, and the soul's post-mortal existence (Questions 84-89). Pasnau frankly characterizes Part I as the "most difficult and tendentious" in the work. In keeping with the initial suggestion of novelty, I shall focus on some of the distinctive interpretations that Pasnau proposes. In chapter 1, Pasnau explains how Aquinas rejects the reductive materialism of the "ancient naturalists" (as Aquinas calls them), which holds that the soul is itself some kind of body, in favor of a "reductive hylomorphism" (44). A human being is a composite of matter and form, but the two constitutive principles are conceptually, but not really, different. Though not the standard interpretation, Pasnau pursues it as a viable middle way between materialism and dualism. He concludes with the astonishing, but not unintelligible, claim that "Aquinas gives us a theory of the soul that actually solves the mind-body problem...in a thoroughly satisfying way" (140).
In the second chapter, he takes up the main burden of Q.75 to establish the soul's subsistence (its capacity for independent existence) and imperishability. On this point Pasnau's typically sympathetic approach to Aquinas runs out. The first difficulty he calls attention to is that the human soul seems to be only weakly subsistent (meaning that it subsists only as part of something larger that is strongly subsistent, like a human being). The second, more serious problem concerns the central argument in 75.2 that the knower knows all material things, but would be impeded from doing so if it had any material thing in its nature. Pasnau thinks this argument fails inasmuch as it relies on a supposed link between intentional existence and concrete existence, such that if x exists concretely in the mind, it also exists there intentionally (or cognitively), but that precludes the simultaneous intentional existence of y and z. Using the example of a bitter tongue that can taste nothing sweet, Aquinas generalizes without adequate rationale to the case of the intellect (57). But instead of merely consigning Aquinas to an unhappy and poorly defended dualism of subsistent soul and mortal body, Pasnau introduces what he calls a "deeper metaphysical account" (71), according to which actuality is more basic than either form or matter. In fact, it is "the unifying element in all being" (see 131-40 for a fuller explanation), and all substances are bundles of actuality. This interpretation, Pasnau admits, is "highly unorthodox" (132), and rests more on its explanatory power than any textual evidence confirming it (136). Instead of thinking that there are two types of stuff, material and immaterial, and so embracing either materialism or dualism, Pasnau's Aquinas has two kinds of actuality -^× material actuality, which is subject to alteration, generation and corruption, and immaterial actuality, which transcends those constraints. Most significantly, this reading of Aquinas's metaphysics has the power to remedy the argumentative defect in establishing the soul's subsistence. To say that the rational soul is a subsistent form is not then to claim that it mysteriously separates from matter, but that it has such actuality as to be capable of independent existence.
Perhaps the most obviously "tendentious" material in Part I comes in chapter 4, which takes us onto ground not covered in the Treatise -^× namely, how human life begins. Here Pasnau employs Aquinas's position on the delayed infusion of the rational soul against the thesis favored by the Catholic Church that human life begins at conception. The argument he offers has much to recommend it, but Pasnau never stops to wonder whether Aquinas, if alive today, would maintain a position at odds with his Church's teaching. Yet Pasnau's strategy is precisely to use both Aquinas's authority and his arguments (their medieval biology much refined and updated) to show "what is wrong with the Church's position" (105).
Part II is more expository in nature but contains its fair share of striking claims. For example, in chapter 5 Pasnau argues that it was necessary for Aquinas to make a real (not merely conceptual) distinction between the soul and its capacities (potentiae) because his rejection of a plurality of substantial forms required it, as did his epistemological doctrine that we come to know the soul's essence only through its capacities. In chapter 6 he presents an interesting argument for the way in which the common sense power, which unifies the particular information from the five proper senses, might be defensible today, even if there is no "spatially unified terminus for all sensory cognition" (199). In chapter 7, against the standard reading of Aquinas as a libertarian, Pasnau contends that Aquinas should be understood as a compatibilist, despite the fact that Aquinas often appears to say the opposite. On Pasnau's reading, this does not mean that Aquinas endorsed any form of physical or psychological determinism, but rather that "Aquinas explains human freedom without any recourse to an uncaused, undetermined act of will or intellect" (221).
Part III takes up the processes of intellectual cognition. In chapter 10, in interpreting 84.5 on the Augustinian theory of divine illumination Pasnau shows that he has changed his mind since his first book, Theories of Cognition in the Later Middle Ages (1997), where he held that Aquinas effectively repudiated the doctrine while paying it lip-service. He now believes that "Aquinas intends nothing less than to affirm Augustine's theory and place it at the very heart of his own account of intellective cognition" (307). His interpretation is that Aquinas is distinctive by virtue of supposing that all illumination is given from the start, "bottled up within the agent intellect" (306). So the agent intellect is the locus of divine illumination in us, without which we could not acquire the most basic concepts and first principles. In this way Aquinas is not a naturalist when it comes to knowledge; the distinction of being the first naturalist is reserved for Duns Scotus (310). In chapter 11 Pasnau gives an insightful analysis of how Aquinas handles the problem of self-knowledge by dividing it into two different levels of knowledge, "everyday, individual self-knowledge" (which might better be called self-consciousness) and a theoretical knowledge of the mind's nature (337). In particular he aptly characterizes Aquinas's understanding of reflection as "an outward look that is reflected back within" (343) rather than an introspective gaze of a Lockean sort. Consequently, Pasnau can explain how Aquinas's perspective on self-knowledge falls nicely between Lockean introspection and behaviorism into a middle ground which, despite its attractiveness, seems "strangely underpopulated" (348).
In the final chapter Pasnau connects the argument from 75.6 on the soul's imperishability with the assertion in Q.89 that the soul will continue to function after separation from the body. Many have found Aquinas's account of the separated soul's functioning ad hoc and unconvincing. After considering that objection (366), Pasnau develops an interesting interpretation. What is ad hoc in the account is not the new mode of existence involved in such a case, but rather the direct divine intervention to supply images to separated intellectual souls in place of the images normally derived from the senses. In their separated state, souls realize their intrinsic subsistence and exist for a time much like spiritual substances (angels).
All in all, if not entirely persuasive in all of its claims, Thomas Aquinas on Human Nature is a very stimulating read. It is lucidly written and meticulously organized, even if Pasnau cannot quite make good the claim that every chapter, and sections within chapters, can be read independently (xi); the reader is constantly being pointed forward or backward to another relevant section. One odd feature is that there are text-boxes throughout the work which provide additional explication of concepts or themes; I have not quite been able to decide whether these are ultimately helpful or distracting -^× perhaps a bit of both. One other small complaint: Pasnau frequently treats the opening objectiones and sed contra's of the ST's articles as views that Aquinas himself holds. This is misleading: the sed contra's are citations of authorities that must be taken seriously by a theological master making a determination, and the opening "objections" are just arguments that serve as raw material for the Master's response. But these are at most minor blemishes on a major achievement that blends extensive textual research with adventurous philosophical interpretation. It is highly recommended to philosophers, especially those wont to suppose that Aquinas is inextricably medieval. Yet it will equally well reward the efforts of all those who can follow its sometimes demanding philosophical contours.