Near the beginning of the extended account of normative judgements set out in the first part of the second volume of the Summa Theologiae [hereafter ST], Aquinas offers a detailed analysis of the components of human action, beginning with an analysis of the human act generically considered (I–II, 18), proceeding to a consideration of the interior act of the will (I–II, 19) and the exterior act (I–II, 20), respectively, and concluding with an analysis of the consequences of goodness or evil in human acts, that is to say, rectitude and sin, praise and blame, and merit and guilt (I–II, 21). It is clear that Aquinas regards this analysis as central to his overall normative theory – he explicitly says that if a particular act is to be regarded as morally good, each of its components must be good – that is to say, the act must be good in kind (that is, its object must be good), done for a good end, and appropriate to the circumstances (I–II, 18.4, ad 3). It thus matters a great deal, on his terms, to be able correctly to identify and analyse the characteristic components of a human act.

The distinctive language, if not the substance, of Aquinas's analysis of actions dominated debates in Catholic moral theology until the turn of the century, and continues to play an important, if not so central a role in Catholic thought to this day. For this reason, Catholic theologians may not realize just how odd Aquinas's analysis sounds to many of our contemporaries. What is more, even those who are most sympathetic to Aquinas's moral theory, including Catholic philosophers and theologians who draw heavily on it, commonly find his analysis of the human act bewildering. Nor is this reaction surprising. On any showing, the detailed analysis of the human act set forth in I–II, 18–21 comprises one of the most puzzling and difficult texts in the ST. Aquinas's analysis is couched in terms that are by no means perspicuous – including not only the language of object, end and circumstances familiar from the ST, but also matter and motive, both of which feature more prominently elsewhere in Aquinas's writings. The interrelationships among these terms are not always clear, and they are developed along lines that are not always evidently consistent.

In The Specification of Human Action in St Thomas Aquinas, Joseph Pilsner attempts to sort through these difficulties by providing an analytic account of the various components of the human act that Aquinas identifies, seen in themselves and in relation to one another. In doing so, he goes beyond the ST to include nearly every discussion of human acts throughout the Thomistic corpus. As a result, he includes a consideration of components that are not treated, or discussed only in passing, in the ST; with respect to the more familiar components, he identifies complexities and nuances in Aquinas's overall account that the ST, taken by itself, does not convey. The result is a remarkably useful and illuminating book. To my knowledge, it is the only book currently available which offers this kind of comprehensive, analytic survey of Aquinas's texts on human action.

Pilsner has rendered an important service to Thomistic scholarship simply by collecting these texts. What is more, his analysis offers an invaluable guide through complex discussions. His interpretations of specific texts are not always persuasive, at least to this reviewer, but the overall success of his book does not depend on any one reading of a particular text. What matters more is his overall thesis that the complexities of Aquinas's analysis can be shown to reflect an underlying coherence and consistency, in spite of surface incongruities. Pilsner makes a good case for this overall thesis, arguing point by point that the seeming inconsistencies in Aquinas's account can be resolved, or at least relegated to the margins of his account, through careful analysis of the full range of the relevant texts.

Pilsner's book will thus be of interest to anyone who gives sustained scholarly attention to Aquinas's texts, or who regularly teaches them. Yet in one respect, he offers less than he might have done to potential readers who are not Thomists, or at least regular readers of Aquinas. More specifically, he offers little in the way of context to help the non-specialist to see what might have motivated Aquinas's own analysis, or to suggest why that analysis might merit respectful attention from philosophers and theologians today.

To a very considerable extent, we can account for Aquinas's distinctive approach to moral analysis, including many of its most puzzling features, by placing his treatment of the moral act within the context of widespread debates over sin and virtuous action beginning in the late eleventh century, and continuing in full force through Aquinas's time (and beyond). To a very considerable extent, this debate turned on an analysis of the ways in which the overall value of an action and its distinct components both stem from and partially determine the agent's will, for good or evil. Thus, it was frequently said that some actions are bad in kind, such that they cannot be redeemed by good motives or a good end, because they bear within them some intrinsic disorder or deformity. The language of disorder/deformity, in turn, at least suggests, even if it does not require, an analysis of the characteristic components of the human act, if only to provide a context for identifying what is disordered in relation to what. This analysis is cast in terms that Pilsner finds in Aquinas's discussions of human acts, but characteristically (in Aquinas), not in any developed or centrally important way – the matter of the act, its motive, and the circumstance as correlated with due matter.

Once we realize that Aquinas is self-consciously appropriating, but also re-casting, the terms of long-standing debates, his treatment of these obscure terms is more comprehensible, and their relation to the mature analysis offered in ST, I–II, 18–21 is easier to trace. An analysis that had been couched in the rough terms of matter, due circumstances, and end is now re-formulated in terms of more finely grained distinctions among the object of the act, the agent's end in acting, and circumstances, the latter reinterpreted to comprise all those features of the act which contribute to its overall degree of sinfulness or merit without changing its essential moral character. These distinctions are offered as a more precise way of capturing the insights and concerns of earlier and contemporaneous debates over the relation between the agent's act and her sinfulness or merit. As such, they represent Aquinas's contribution to an ongoing process of developing a moral psychology of virtue and sin.

I do not want to give the impression that Pilsner has nothing at all to say about the historical context of Aquinas's analysis, but his remarks on this topic are brief and occasional, and seem to rely almost entirely on secondary literature. In all fairness, Pilsner wants to consider Aquinas's account on its own merits, not as a historically situated intervention in a specific set of debates. Yet more attention to the latter gives us a better sense of the distinctiveness of Aquinas's analysis than we could otherwise obtain. More specifically, once we locate Aquinas's analysis in its immediate context, we are in a better position to make sense of the seeming inconsistencies in that analysis.

It is tempting to account for these difficulties by arguing that Aquinas is burdened with a traditional vocabulary which he must accommodate, but which fits badly with his basic view, namely, that the moral species of the act is determined by the overall stance of the agent's will towards good or evil, or else, its orientation towards discrete intelligible goods. Yet once we take account of Aquinas's own context, we see that he does not simply take over an inherited vocabulary – which for him would have comprised the analysis of actions in terms of matter, circumstances, and motive. He is certainly aware of this language, as Pilsner amply shows, but by the time we come to the ST we find him relegating some elements of this traditional vocabulary to the margins of his discourse, and reformulating others. The resultant analysis is couched in the more familiar terms – more familiar to us, at any rate – of the object, end, and circumstances of the act. But it is important to realize that this language reflects Aquinas's innovative reinterpretation of a received discussion, not his dutiful (or careless) appropriation of a set of givens. This, in turn, suggests that Aquinas really is committed to the terminology and the intricate analysis of I–II, 18–21. Something is at stake for him here; he wants to make a point that he could not have made, or made so perspicuously, through the older terminology of circumstances, matter, and motive.

Just what might that be? It would go well beyond the scope of a brief review essay to attempt a full answer to this question. We can get at least a sense of the issues at stake, however, through considering what Pilsner rightly identifies as one of the central conundrums in Aquinas's mature analysis of the human act, namely, the complex interrelationships among the object of the act, the agent's overall end, and the circumstances of the act. As Pilsner notes, the object is sometimes said to determine the ratio (that is, the formal, defining principle) giving the act its species, while at other times, it is said to be the proximate act of the will. This claim is not so paradoxical as it may appear to be; it depends, rather, on a distinction between the exterior act, considered as a token of a specific type of act, and the interior act of the will, considered as the concrete act comprising a generic kind of action, chosen for a specific end, in light of a particular set of circumstances.

Considered as the defining ratio determining the species within which an exterior action should be subsumed, the object is formally distinct from both the agent's end and the circumstances (I–II, 18.2,5; I–II, 18.10, 11). However, considered as the terminus of the agent's will – thus, as constituting the interior act – the object is constituted by the agent's aims, the circumstances, and the object of the exterior act, globally considered as comprising one concrete action (I–II, 18.6). If there is an intrinsic causal connection between the object of the exterior act and the agent's aim in acting, then the former is subsumed under the latter into one object; otherwise, they remain distinct, in such a way as to locate the act within two distinct species at once (I–II, 18.7).

To some extent, the terms of this analysis, including the critically important concept of the object of an act, are Aquinas's own, and to the extent that he incorporates older terms of analysis, he interprets them in new ways (most notably, in distinguishing circumstances from object in the way that he does). Again – what is at stake for him here? In part, Aquinas's reformulated terminology and the main lines of his analysis reflect his overall metaphysical analysis of human action, considered as a distinctive form of causality. (On this point, see Stephen Brock's 1998 study, Action and Conduct: Thomas Aquinas and the Theory of Action (Edinburgh: T. & T. Clark).) More specifically, Aquinas's distinctions allow him to make a real advance in a long-standing debate.

Are good and evil in human actions constituted fundamentally by the inner act of the will, or by the exterior act? Aquinas replies that it depends. Insofar as the goodness or evil of a particular act stems from the end for which the agent acts, this does depend on the will, and in this respect the goodness of the exterior act is dependent on the goodness or evil of the interior act of the will. At the same time, the goodness or evil of the exterior act, considered as a token of a kind of action, depends on reason, which is to say, it depends on the appropriateness or otherwise of the object of the act, considered as the terminus of the agent's causal power (I–II, 20.1). For this very reason, there is a sense in which the goodness of the exterior action adds to, and indeed partially determines, the good of the interior act of the will (I–II, 20.4). That is, the exterior act, considered as a representative of a kind, can inform the inner act of the choosing will because it has a rational structure, of appropriateness or equity or their opposites, that can be discerned by reason. In this way, the exterior act has an independent moral significance – expressed through its object – that determines the sinfulness or merit of the agent choosing it.

Thus, the distinct components of human action come together to specify the concrete act, independently of the global orientation of the will towards good or evil, or even its orientation towards distinct intelligible goods, considered in abstraction from the causal structure of the concrete act. To put it another way, the overall stance of the will towards good or evil is determined by what it is that the agent concretely wills. This implies that if an agent knowingly chooses to perform an action that is defective with respect to any of its components, her will is corrupt – even though she does not choose the act as defective. On this view, neither the agent's generic desire to do the good, nor the orientation of her will towards basic goods (taken by itself) can render her will good. This is a striking claim – most of our contemporaries would find it deeply counterintuitive, and it would be denied by most Catholic moral theologians representing the whole spectrum of liberal and conservative views. Yet there is a case to be made for it, particularly in light of the metaphysical and theological commitments that inform it. This is not the place to attempt to make that case – my point is simply that Aquinas's position, seen in its immediate context, poses a more comprehensive and radical challenge to the main lines of contemporary moral theology than we commonly realize.

For this reason, I would suggest that Pilsner could have done more to help his readers see the contemporary significance of Aquinas's theory of action by locating that theory more firmly in its own immediate context. In saying that, however, I do not by any means want to undervalue what Pilsner has done. It is to be hoped that he will turn to some of these issues in subsequent volumes; meanwhile, future work on Aquinas's theory of action will need to take account of this comprehensive and insightful study.