In the past few decades the cognitive and behavioural sciences have challenged presumptions about the nature of human understanding. Broadly speaking, the trend has been to show that a reductive conception of science is incapable of providing a comprehensive conceptual framework for understanding the world, and that our rational processes are imbued with systematic limitations. For the natural theologian this may be both a reassurance and a challenge. Scientifically reductive understandings of the world are on such accounts insufficient, leaving open the possibility of a broadly-based natural theology, whilst questioning to some degree the role of reason and cognitive resources on which both scientific reductionist and natural theologian rely.

It was therefore fitting that five speakers from five different subject areas whose work relates to the cognitive and behavioural sciences were assembled to give jointly the 2001 Gifford Lectures in Natural Theology at the University of Glasgow on the topic of ‘The Nature and Limits of Human Understanding’. All are highly distinguished in their respective fields, though it is possible that many theologians will not be familiar with their work. Each speaker gave two lectures, and this volume is the edited text of the ten lectures.

Philip Johnson-Laird in his two lectures discusses the limited nature of our unaided mental capacity to model problems. Using a variety of simple examples, he shows how predisposed thinking and working memory with limited capacity result in basic logical errors in problem-solving. Take the simple case where X prevents Y and Y causes Z. This generally results in people concluding that X prevents Z, ignoring that Z could have other causes and that X need not therefore prevent Z. Using more sophisticated examples, Johnson-Laird argues that those who reached such false entailments were misled by the added complexity of incorporating all the possibilities allowed by the initial description, which requires greater mental capacity. His point is that this is far from being an isolated example and may be regarded as a systematic feature of much of human reasoning.

George Lakoff in his lectures questions the claim that we can have knowledge of the world which is not embodied, in the sense of not incorporating features of our physical natures. What Lakoff argues is that the structure of the modelling of the learning of, say, verbs of hand motion, has the same basic structure as certain linguistic features, such as the grammatical aspect of verbs. From this he argues that we come to understand the world in terms of what our bodies can do. This is reflected in the metaphorical language used to express causal concepts: ‘The noise gave me a headache’ or ‘He pulled me out of my depression’. Thus, he concludes that our embodied nature is a constitutive feature of our conceptualisation. That is, we cannot understand the world in a way unaffected by our physical bodies.

These critiques of any claim to a comprehensive impersonal description of the world are extended in Lynne Rudder Baker's more directly philosophical lectures on the logic of epistemology. She focuses on the constraints on understanding due to the logical distinctness of first-person and third-person perspectives. Thus, indexical items of knowledge involving first-person claims (e.g. ‘I’ or ‘now’) cannot be reduced to the third-person. If so, an impersonal description of the world cannot express the first-person perspective, which means that there can be no fully comprehensive conception of the world expressed in such ‘neutral’ terms. Therefore, any claim to a pure objective science must be dropped.

Michael Ruse continues the assault upon impersonal analyses, in this case on conceptions of ethics which make claims to universality, by arguing that many features of our ethical behaviour are explained by evolutionary principles. Sounding what is perhaps the only reductionist note in the book, he argues that this leads to ‘a scepticism… about foundations rather than about substantive dictates’ and that ‘the Darwinian approach to ethics leads one to a kind of moral non-realism’(p. 152). This is perhaps too hasty a conclusion, given accounts in virtue ethics, by, for instance, Foot and Hursthouse, which combine moral realism with ethical naturalism.

In what is the only explicitly theological contribution, Brian Hebblethwaite argues that whilst theology requires metaphysics for its proper articulation, theology can also enrich a philosophical understanding of the world. Theology can provide philosophy with clues to resolving antinomies and providing foundations for some of its assertions. It is a fitting coda, even if its balanced tone means that it says little to surprise the theologian sympathetic to philosophy.

Given the diversity of disciplines represented, psychology, linguistics, philosophy and theology, what is particularly satisfying is the degree of convergence between the speakers. In this they mirror the direction of the debate at present. Instead of a crude polarity between the scientistic positivist on the one hand, and the sceptic or relativist, on the other, each of the speakers argues for what might be considered a middle position. The nature of our understanding is largely determined by human nature and individual perspective, and we should have a healthy awareness of that. The very fact that one can stand back to some degree and analyse this testifies to the view that these irreducible components in our processes of reasoning do not quench its more universal aspect.

Each of the speakers had only two lectures in which to present the subject area and to make a case, and therefore it is not surprising that there is little in this collection which is new. However, in giving concise overviews of a diversity of subjects and providing examples to support specific arguments, I do not see how they could have done much better. In addition, that there should have been so clear a collective convergence adds strength to each of their positions, making what might have been a diffuse volume remarkably unified. Anthony J Sanford has chosen his speakers well. A splendid book, and of interest to far more than theologians.