Thomas Nagel has been one of the most influential philosophers of our time. His seminal article “What is it like to be a bat?”, published in 1974, started a revolution in what is now known as “consciousness studies”, by arguing that the subjective quality of conscious experience (for example what it is like to smell a rose, or taste coffee) cannot be captured by even the most exhaustive scientific account of a subject’s behaviour or the workings of its brain or nervous system. More recently, his Mind and Cosmos (2012) outraged the scientific establishment by maintaining that Darwinian principles (random mutation plus natural selection) could not, in the time available, have been sufficient to account for the emergence of conscious thought as an “instrument of transcendence, able to discern objective reality and objective value”.

Nagel’s philosophical writing has always avoided the ponderous stylistic contortions and pseudo-technical jargon found in much contemporary anglophone philosophy, and the latest offering is as incisive and crystal clear as ever. The book opens with an account by the British philosopher Stuart Hampshire of an incident from his service in British military intelligence during the Second World War. Shortly after the Normandy landings, he was sent to interrogate a collaborator captured by the French resistance, who was known to possess information of vital importance to the allies. The head of the resistance told Hampshire he might go ahead with the interrogation, but said that when he was finished they would shoot the prisoner, as they always did in such cases. Left alone with Hampshire, the prisoner said he would reveal nothing unless Hampshire gave his word that afterwards he would be handed over to the British. Hampshire replied he could not give such a guarantee, and as a result, the prisoner told him nothing before he was shot by the French.

How should we judge Hampshire’s decision? There is an apparent standoff here between two distinct moral perspectives. On the one hand, if we weigh up the likely consequences in terms of benefits and harms, we may feel the right action is simply the one that leads to the best outcome: by giving a false promise, Hampshire might have gained information that could have saved many allied lives. On the other hand, we feel the force of Hampshire’s gut reaction that to have falsely given his word was something he simply could not do: it would have been wrong in itself—wrong independently of any cost-benefit calculation of likely consequences.

The moral theory known as consequentialism, of which the best-known variety is utilitarianism, aims to eliminate the standoff by insisting that the general good should always take precedence. On the most radical version of this view, Hampshire’s gut feeling that he simply could not break his word is simply an irrational taboo, or piece of squeamishness, and the rational moral agent will simply choose the course likely to produce the best results (in this case, doing whatever is necessary to gain the information that would save many lives).

Nagel acknowledges the rational appeal of this “external” perspective, which impartially calculates the best outcome, taking into account the interests of all involved, with “each counting for one, and none for more than one”, as Jeremy Bentham, the founder of utilitarianism, once put it. But for Nagel this cannot be the whole story. For there is another moral perspective from which there is something inviolable about individual rights and duties (such as the duty to keep one’s word, or the right not to be lied to and manipulated as a means to an end). In such cases, Nagel observes, “the inviolability of the individual facing us dominates the rival claims of those we could help by sacrificing him to the general welfare” (p. 21). This sense of inviolability might be eroded if the moral outlook of future generations were to develop in a more consequentialist direction, but Nagel argues that if this happened it would not really be moral progress. For something would be lost—the “vital part of our lives” which consists in “treating each [individual] decently come what may, and demanding such treatment for ourselves” (p. 21).

In the second of the two essays that make up this short book, Nagel reflects further on the question of moral progress. We like to think that our moral outlook has advanced compared with that of previous generations—for example in so far as our legal system no longer countenances cruel punishments like flogging, or the use of torture to interrogate suspects. But if our now regarding such things as wrong amounts to genuine moral progress, this implies that our moral perception has improved, so that it now better reflects what is objectively right or wrong.

Does this mean that moral progress is analogous to scientific progress? Are we to say that just as, in finding out that salt consists of sodium chloride, we have come to know a feature of reality that was true all along, so in coming to see that torture, for example, or slavery, is wrong, we are coming to appreciate a moral truth that has always held, even when people did not recognise it?

As suggested by his conception of the mind as an “instrument of transcendence able to discern objective value”, Nagel is strongly drawn to a realist or objectivist conception of morality. He has little sympathy for the deflationary views of morality such as emotivism that found favour in much of the twentieth century, where moral judgements were regarded as no more than expressions of subjective preferences and desires. On the contrary, Nagel clearly believes there are objectively right answers to difficult moral questions.

In the case of science, we take it that our theories are correct in so far as they (at least approximately) reflect the way the natural world actually operates: scientific knowledge tracks the truth about the natural world. But what, for a moral realist like Nagel, is the basis or ground of moral truth? The traditional religious answer, that moral truth stems ultimately from God, is not even considered by Nagel, who is elsewhere on record as declaring himself an atheist, and adding, somewhat weirdly, “I hope there is no God; I don’t want the universe to be like that!” If we reject the religious answer, an alternative, which is canvassed by Nagel, is “a Platonic realm in which moral truths have their being, metaphysically separate from the natural world and the people in it”. But Nagel rejects this too: “realism about morality, as I understand it, does not imply such a metaphysical picture” (p. 24). So what are moral truths about?

Nagel answers that morality is “an aspect of practical reasoning: it concerns what we have certain kinds of reasons to do and not to do” (p. 24). But what is the status of these reasons? Here, the analogy with scientific realism breaks down, for these reasons are not like chemical elements waiting to be discovered. Rather, says Nagel, they refer to “irreducibly normative truths” (p. 25). Yet, at this point, the clear flow of Nagel’s argument seems to falter. For what makes these normative (that is, authoritative and action-guiding) truths true? Nagel replies that nothing makes them true; they are “just true in themselves” (p. 34).

Perhaps all explanation must stop somewhere, but this closure strikes me as too abrupt for comfort, and Nagel’s moral realism thereby risks tapering off into mere assertion. At all events, the remainder of the book is largely concerned with the question of how far these “normative reasons” are accessible in any given stage of human social development. Nagel’s answer is “it depends”. For example, the reasons in favour of the right to freedom of expression were, he argues, simply not accessible in the pre-modern world, which lacked any conception of political legitimacy based on consent. So the “ethical time traveller”, to use a phrase coined by Nagel’s near contemporary, the late Bernard Williams, cannot plausibly blame earlier generations for failing to recognise this right, since the liberal conception of freedom of expression was simply out of their conceptual reach. By contrast, in the case of slavery, its wrongness was, on Nagel’s view, true “all along”, and the reasons against it could in principle have been recognised by the ancient Greeks: “it is hard to believe they did not have access to the sense that there was something sickening about slavery” (p. 48).

As may be seen from these examples, Nagel’s discussion has crucial relevance to many of the problems that dominate contemporary discussion about how far people are to be held to account for behaviour (for example in the sphere of sexual conduct) which now attracts condemnation but which was not widely censured in the climate of earlier times. If Nagel is right, this will hinge on how far those who grew up in an earlier ethical climate were capable, given sufficient imaginative effort, of appreciating the relevant moral reasons.

Nagel ends his wide-ranging discussion with the sobering thought that “we should regard our present moral convictions with a certain humility in view of the contingency of our place in history”. Future generations may well lament our failure to acknowledge moral truths that “we are now too pig-headed, dishonest, or self-deceiving to recognize, but that are nevertheless accessible to us and therefore already apply to us” (p. 69).

Many of the ideas in this slim but philosophically weighty volume revolve around what Bernard Williams (often an implicit and sometimes an explicit antagonist in Nagel’s argument) once described as the “radical contingency in our current ethical conceptions”, namely that “they might have been different from what they are” (Truth and Truthfulness (2002), p. 20). The spectre of contingency threatens the traditional idea of the “eternal verities”—timeless moral truths implanted in the human soul and illuminated by the God-given light of reason. With the gradual erosion of the theistic worldview in our culture, and the rise of the Darwinian framework, attention has shifted to the evolutionary origins of human morality, and this has reinforced the sense, first highlighted by Friedrich Nietzsche in Beyond Good and Evil (1886), that our cherished moral convictions might be the result of a long series of historical and developmental circumstances that might have been otherwise. As Nietzsche put it, “the real problems of morality only emerge when we compare many moralities; for when philosophers have tried to supply a rational foundation for morality this was just another fact within a particular morality”.

Drawing on these sceptical and subversive foundations, Bernard Williams insisted that what philosophers call “reasons for action” can have no ultimate foundation apart from our purely contingent set of motives and desires. In the end, reasons for action can only be what Williams called “internal” reasons (“Internal and external Reasons” in Bernard Willaims’s collection Moral Luck (1981)). Morality is thus “naturalised”—ethics is ultimately reduced simply to contingent facts about human psychology. This disturbing picture is, in my own view, deeply mistaken; but at least it is consistent with the uncompromisingly naturalist worldview that dominates contemporary philosophy.

What Nagel has given us, by contrast, is an uneasy compromise between the naturalistic framework and his own residual yearning for transcendence and objectivity. That residual yearning prompts him to insist that there are indeed correct or incorrect, right or wrong, answers to the moral questions that we wrestle with. And the right answer in any particular case does not depend on the course of action that we, or our group, or our society, actually desire or choose. There is, as Nagel succinctly puts it, a “gap between truth and performance that makes the answer normative rather than merely psychological” (p. 51, emphasis supplied). But until he can supply some secure foundation for that “normativity”, Nagel’s objectivist and realist moral aspirations, so it seems to me, must remain unfulfilled.