Houck opens by speaking of original sin as the invention of Augustine, as without biblical basis, and unintelligible by dint of our evolutionary worldview. But he means only to grab our attention, and he succeeded in annoying me for a few moments. Once this initial rhetorical assault is over, he offers an enjoyable and stimulating text aimed at retrieving a medieval take on an ancient doctrine for a modern audience. He treats the biblical and earlier patristic roots of the doctrine with the utmost seriousness as expressing a universal need among all human beings, including infants, for the deifying grace of Jesus Christ. Drawing on Aquinas, Houck proposes a ‘new Thomist view’ of this need, which can negotiate the challenges of evolutionary theory. However, whether in Thomist terms this successfully equates to a doctrine of original sin is by no means so clear.

In chapter one Houck helpfully sets Aquinas in the context of Augustine's mature account of original sin and how its ambiguities were represented in Anselm of Canterbury, Peter Abelard, and Peter Lombard. Identifying their theories respectively as realist, legal, and physical/disease, Houck associates Aquinas with the last of these: original sin is understood along the lines of an infection of human nature transmitted from Adam. Houck lays the ground for his critical retrieval of Aquinas's theology of original sin in chapters two to five, paying careful attention to the different meanings of nature in Aquinas in chapter three and in chapter four finding fault with his account of how original sin is to be construed as voluntary. While human nature's survival of the Fall is a positive point for Houck's ‘new Thomist view’, the voluntary character of original sin is more easily set aside, since Houck is aiming at an account of ‘originated original sin’ in us which is not dependent on any ‘originating original sin’ in the will of any Adam. The Fall from original justice proves surplus to Houck's requirements for vindicating original sin in the face of evolution, and he is more concerned with the need for supernatural grace found in human nature as it is transmitted from generation to generation.

Houck is chiefly wary then of the link Aquinas accepts between original sin and a historic state of original justice. In chapter two he reconnects with the early-twentieth-century neo-scholastic debate on Aquinas and the relationship between that state and the habit of sanctifying grace. Though the debate was described at the time as ‘spirited’, Houck's own presentation of it does not fail to dial things up a little: scholars ‘drop bombshells’ and so on. The overall rhetorical effect is to intimate that Aquinas's writings are more problematic than they really are (some inconsistencies seem more terminological than real) and can only be mined for a solution in the company of a thoroughly modern rethinking of original sin, which Houck judiciously provides.

At first Aquinas allowed the possibility that there had been two justices prior to the Fall, original justice and a further supernatural gratuitous justice, and reported on a contemporary difference of opinion on when the latter grace was bestowed, whether at creation itself or later. Houck takes Aquinas to have been committed to a total distinction between justices and hence to the transmissibility of original justice independent of supernatural grace. Acknowledging that Aquinas leaned early on towards the creation of the first human beings in grace, Houck quite properly focuses on the key development in his thinking, whereby the various right orderings within original justice are seen as causally dependent on sanctifying grace, such that that supernatural habit enters into the very notion of original justice itself. Houck intriguingly suggests that Aquinas does not follow through on the implications of this move for the transmissibility of original justice. Aquinas certainly never departed from his early position that grace, like the human soul, was divinely ‘infused’ rather than parentally ‘transfused’. However, once grace is recognized as part of original justice, transmissibility surely requires revisiting. Houck hints that Aquinas was moving this way.

Whenever more traditional Thomists become convinced that Aquinas's position was not finally settled in its dynamic development, it seems to me proper for them to experiment in continuing his own trajectory, re-employing his own theological principles, including his example of commitment to the authority of conciliar teaching. In this case, that would surely include adherence to Trent's teaching on original justice. To be fair, when Houck comes to his own proposal in chapter 7, he does indicate how he might link his own view to the Fall and originating original sin. Unlike Aquinas, however, Houck is not a Catholic, and his ‘new Thomist view’ of originated original sin arises out of a more recent and growing ecumenical interest in what can be usefully received from Aquinas into today's theology, broadly conceived, where it is widely held that there was no historical Fall. Houck's object is to derive from Aquinas an account of original sin that can satisfy both those who accept a historical Fall and those who do not, and he approaches his goal by way of treating Aquinas's theory of original sin as separable from that of original justice.

By insisting that, for Aquinas's own overall theory to work, it must preserve a precise parallel between the transmissibility of original sin and that of original justice, Houck's purpose is to place and leave him on the horns of a dilemma. Either original grace would have been transmitted through human reproduction by way of instrumental causality (something Aquinas denies) or original sin would be just as much caused by God as original justice would be (something Aquinas could hardly accept, since it would make God the direct cause of evil). Houck thus justifies himself in abandoning Aquinas's theory for a portion of it. Rather than treat original sin as the loss of original justice, Houck defines it as a lack of sanctifying grace.

Houck contends that this result provides him with something modern positions from Kant onwards, as examined in chapter five, do not. While rejecting a historical Fall, they have reduced nature to evil, excluded infants from the need for Christ, or failed in some other way. On Houck's view, we are all by nature turned to God, but without the supernatural means to meet our heavenly goal, and it is a humanity naturally lacking grace that is transmitted by human generation. Such a view of original sin, set out in chapter seven, is also compatible with the challenges from evolution which Houck outlines in chapter six, since original sin is a lack of grace rather than a corruption of nature or DNA. Admittedly this is a far easier task than facing the challenges of evolution to a historical Fall, such as the question of monogenism and polygenism, on which Houck gives some pointers.

Houck's final chapter, where he responds to what he supposes to be relevant objections to his proposal, takes him wide off course. I was surprised he devoted space to a possible incompatibility of his theory with de Lubac's notion of natural desire for the supernatural – a consequence which would surely strike no careful reader. My own concerns were more closely tied to original sin itself. Although Houck speaks of it as a ‘privation’ (p. 201), he in fact seems to regard it as a lack rather than a loss. Though he speaks of it, even in infants, as ‘a sinful act of being’ (p. 219), he does not treat it in terms of being turned away from God, as Aquinas does. Instead he derives from Aquinas the view that the ‘formal cause of original sin’ is ‘the natural orientation to nature's author’ (p. 202). Such a lack as Houck proposes at the point of origin of each one of us may be ‘original’ – but is it ‘sin’?