Pretty much no one questions the moral legitimacy of the Nuremberg trials. The basis of that legitimacy is usually held to be that there are core moral truths that are epistemically accessible and applicable to all rational human beings by virtue of a common humanity. Such views are also central to natural law positions in ethics. Yet, despite the consensus that the Nuremberg trials were justified and the largely natural law basis for the ethical justification, natural law perspectives are widely overlooked in the largely secular academy.

Some advocates of natural law positions attribute the lack of academic support to the common misperception (they claim) that natural law perspectives require theistic underpinnings. After all, much writing in the natural law tradition exhibits commitment to theism. Yet some defenders of natural law reply that a major strength of natural law ethical approaches is that they can provide comprehensive ethical accounts in fully secular terms, even if they can also be enriched by theistic insights. John Finnis is an example of an advocate of natural law in ethics who holds this latter position.

Some religious advocates of natural law ethical perspectives agree with secular detractors of natural law, that it needs religious underpinnings for adequacy. John Milbank, for example, holds that any natural law ethical account in wholly secular terms is inevitably seriously deficient due to a false conception of the natural as separable from the workings of divine grace. Jean Porter presents a less straightforward position: roughly, natural law on purely philosophical terms upholds a plurality of moral conclusions (in that respect in keeping with much of the liberal secular zeitgeist) and such accounts can be comprehensive and satisfactory on their own terms; yet, more precise resolution on substantive ethical content requires theological input and, anyway, the thought of major figures of the natural law tradition such as St Thomas is more amenable to forms of moral pluralism than is often thought.

In this well-argued and highly stimulating book, Gregory Morgan argues for the bold thesis that the works of John Finnis, Jean Porter, and John Milbank, despite their differences on the secular, have in common that the content of their work on natural law has been impacted upon by conceptions of the secular in relation to the theological in ways that are under-acknowledged and under-scrutinised by the authors. Their work contains what Morgan calls a ‘theological unsaid’.

As Morgan puts it in the case of Porter:

Take the case of Finnis. Although the bulk of natural law thinkers had hitherto been highly critical of the view that there is an insurmountable ontological and/or epistemological gap between what is and what ought to be, Finnis provides a natural law ethical account that upholds a form of the doctrine of the is/ought gap. Not to have done so would have risked his natural law theory being rejected as violating a position taken for granted by many in the secular academy but standardly rejected by those with theist commitments, most notably many Thomists. Finnis ably defends his natural law position on its own terms, without conceding that it represents a strategic accommodation to the secular. But, as Morgan recounts, Finnis in some of his writings can be interpreted as suggesting that such strategic factors might well have played a role. Even so, the sort of rigorous scrutiny of the conception of the secular that Morgan advocates is still largely lacking. There is still a ‘theological unsaid’.

Porter’s natural law account, in contrast to Finnis’, is in keeping with scepticism concerning the derivation on purely philosophical grounds of detailed granular moral norms from indubitable and immutable first principles in a manner that is universally compelling. Here, too, there can be suspicions of the ‘unsaid’: that Porter’s position can be understood in strategic terms, her natural law position as congenial to a morally pluralistic culture. As with Finnis, however, Porter is a highly capable defender of her position on its own terms.

What Finnis and Porter also have in common, Morgan thinks, and central to his claim about the need for a scrutiny of the cogency of the secular, is that they both rely on an under-acknowledged commitment to theological extrinsicism and a ‘duplex-ordo ontology’, that:

Milbank provides strong contrast on this front given his commitment to a robustly theological and biblical understanding of natural law. Yet, his work too, Morgan contends, has its ‘theological unsaid’. Morgan argues that Milbank’s conception of the secular is arrived at to a significant degree through his response to interlocutors such as Donald MacKinnon, a philosophical theologian with Kantian sympathies. If Milbank challenges the secular in his attempt to out-narrate the Kantian, and if Milbank’s conception of the secular is shaped by this process of out-narration, Kantian thought can thus have indirect impact on the content of Milbank’s conception of the secular in ways that Milbank leaves largely unsaid. Morgan also queries Milbank’s general interpretation of Kant, which thereby can increase doubts about the security of the foundations of Milbank’s conception of the secular.

In a short review it is impossible to do justice to the richness of Morgan’s careful readings of Finnis, Porter, and Milbank. I have also said little about Morgan’s own attempt at re-narrating the natural law in the light of the positive positions he argues for.

A short review also cannot tackle the many questions Morgan’s arguments might provoke. To give some examples: Even if an extrinsicist anthropology and duplex-ordo ontology played a significant role in how Finnis and Porter arrived at their natural law accounts, need this imply that the content of their accounts is dependent on these positions? Indeed, might a rejection of an extrinsicist anthropology provide positive underpinning for secular natural law accounts similar to those of Finnis and Porter, since the secular could be understood as imbued by the workings of grace? Furthermore, if it is held on theological grounds that there is a harmony between the workings of grace and nature – as per the Thomist dictum that grace perfects nature, but does not destroy it – might there be reason for confidence in the rectitude of thoroughly secular natural law accounts, even if the fullness of natural law requires theological elements? Regarding the need for the careful scrutiny of views, might Morgan have explored more fully what natural law itself is and what makes an ethical account a natural law ethical account? If it is a necessary condition for natural law ethical accounts that core moral truths are in-principle epistemically accessible to rational agents, might not the concern of Finnis and Porter to ensure appreciation by those of secular viewpoints be in harmony with what natural law ethical perspectives should by definition be concerned with? Moreover, Morgan presents us with theological perspectives on the secular; but the voices of those of thoroughgoing secular viewpoints are relatively absent. Might there be a risk of not really understanding the secular from the ‘inside’? Might Morgan thus have his own ‘theological unsaid’? After all, a fully secular natural law ethical account could be, say, in wholly naturalistic terms without any need (according to the author of the ethical account) for reference to the theological (even implicitly), or to self-conscious secularity (even implicitly), simply by overlooking theological matters; just as the account might also ignore a multitude of other matters that do not come to the mind of the author because not considered relevant to their task.

To list these questions is not intended to detract from Morgan’s achievement. Quite the contrary: it is inevitable that a book so impressively and refreshingly argumentative will provoke. Such intelligent provocation, whether it ultimately convinces or not, can contribute richly to the natural law literature, which this book certainly does.