Peter Harrison is an Australian Laureate Fellow and Director of the Institute for Advanced Studies in the Humanities, University of Queensland. His most recent books are The Territories of Science and Religion and Narratives of Secularization.

Steven Pinker is at it again. Several years ago, the Harvard-based cognitive psychologist took time off regular duties to offer some gratuitous advice to humanities scholars about how to "fix" their discipline.

In essence, he advised, be more like the scientists, and please stop pointing out that there are occasional downsides to advances in science and technology.

Frustrated by the ingratitude of his target audience and impatient with their churlish resistance to his recommendations, he has taken it upon himself to show us how it should be done with a new book on the Enlightenment, its legacy and why we need to stand behind it today.

The Enlightenment may seem an ambitious topic for a cognitive psychologist to take up from scratch. Numerous historians have dedicated entire careers to it, and there remains a considerable diversity of opinion about what it was and what its impact has been. But from this and previous work we get intimations of why Pinker thinks he is the person for the job. Historians have laboured under the misapprehension that the key figures of the Enlightenment were mostly philosophers of one stripe or another. Pinker has made the anachronistic determination that, in fact, they were all really scientists - indeed, "cognitive neuroscientists" and "evolutionary psychologists."

In short, he thinks that they are people like him and that he is thus possessed of privileged insights into their thought denied to mere historians. The latter must resort to careful reading and fraught interpretation in lieu of being able directly to channel what Enlightenment thinkers really thought.

This brings us to Pinker's other methodological novelty - quantification. He declares that Enlightenment ideals can be defended "in a distinctively 21st-century way: with data." This is consistent with his previous advice to practitioners of the humanities: more counting (and, presumably, less reading). Advocacy of the data-driven approach also comports with his earlier work in The Better Angels of our Nature , in which a number of long-standing questions about human nature are answered with a series of graphs. Certainly, he cannot be accused of not following his own advice in the present book, which is similarly adorned with graphical "data."

(As an aside, my own prediction is that future historians, if they haven't all been replaced by cognitive psychologists, will regard misplaced faith in data, metrics and statistical analysis as the curse of the twenty-first century. Consider, for a start, the "replicability crisis" sweeping the social and medical sciences. And for those in academe, think also of the incessant and increasing demand that we measure and metricize every aspect of intellectual life. It is one of the saving graces of the humanities that it hasn't fallen for this line, notwithstanding the undoubted insights yielded by some aspects of the digital humanities.)

With these unpromising starting points in mind, we turn to some of the themes of the new book. I say some because this is not intended as a comprehensive book review; not least because the bulk of the book is not really about the historical Enlightenment at all. That said, there is enough material on the Enlightenment to talk about, and it is certainly worth reflecting on one of two of the book's more contentious characterisations of the period.

An Age of Reason?

We can start with "reason." Pinker is an advocate of reason. As the subtitle announces, the book presents "the case for reason, science, humanism, and progress." Pinker frequently refers to the Enlightenment as the "Age of Reason" (a rather old-fashioned label that seems to have been drawn from Will and Ariel Durant's 1961 Story of Civilization).

But throughout the book reason is treated as an unproblematic given, as if we all know what it is and are happy to sign up to Pinker's version of it. Alas, reason is a notoriously slippery notion. Problematizing it and challenging its authority turns out to be one of the signal achievements of the Enlightenment. Pinker seems blissfully unaware of this.

The most cursory sampling of just some of the key figures of the period helps establish the point. If we go back to the beginning of the scientific revolution - which Pinker routinely conflates with the Enlightenment - we find the seminal figure Francis Bacon observing that "the human intellect left to its own course is not to be trusted." Following in his wake, leading experimentalists of the seventeenth century explicitly distinguished what they were doing from rational speculation, which they regarded as the primary source of error in the natural sciences.

In the next century, David Hume, prominent in the Scottish Enlightenment, famously observed that "reason alone can never produce any action ... Reason is, and ought only to be the slave of the passions." And the most celebrated work of Immanuel Kant, whom Pinker rightly regards as emblematic of the Enlightenment, is the Critique of Pure Reason. The clue is in the title.

Reason does figure centrally in discussions of the period, but primarily as an object of critique. Establishing what it was, and its intrinsic limits, was the main game.

If we take the time to read in just a little more depth, John Locke, the leading English philosopher of the Enlightenment, gives us his plain views on the status of reason and science. In the classic Essay Concerning Human Understanding (1689), Locke insists that scientific knowledge, based on experiment, is "but judgment and opinion, not knowledge and certainty." Our knowledge of nature is necessarily limited in scope on account of "the weakness of our faculties in this state of mediocrity." Science, in short, is destined always to be a makeshift operation, falling short of truth, and providing only a measure of material amenity.

For Locke, pretty much all we can know with certainty in this world is the existence of God and our moral duties (along with some mathematical conclusions):

"our faculties are not fitted to penetrate into the internal fabric and real essences of bodies; but yet plainly discover to us the being of a God, and the knowledge of ourselves, enough to lead us into a full and clear discovery of our duty and great concernment."

For Locke, moreover, whatever limited reliability reason has derives from the fact that it is a divine gift - in his own characterizations: a "spark of the divine nature," "the candle of the Lord," "the voice of God." It is on account of this that, while reason turns out to be almost useless as a means of deriving certain knowledge of the world, it can help establish knowledge of God and of our moral duties. This is the context in which Locke advocates reason as our guide.

It is curious, then, to find Pinker breezily insisting that Enlightenment thinkers used reason to repudiate a belief in an anthropomorphic God and sought a "secular foundation for morality." Locke clearly represents the opposite impulse (leaving aside the question of whether anyone in period believed in a strictly anthropomorphic deity).

So, too, Kant. While the Prussian philosopher certainly had little use for the traditional arguments for God's existence - neither did the exceptionally pious Blaise Pascal, if it comes to that - this was because Kant regarded them as stretching reason beyond its proper limits. Nevertheless, practical reason requires belief in God, immortality and a post-mortem existence that offers some recompense for injustices suffered in the present world.

In all of this, Pinker exhibits a common, but confused position on what are quite distinct issues. One is whether we can be moral without religion, to which the answer, empirically speaking, is yes. But whether it is possible to establish an objective content for morality, how we justify moral claims, and whence the normative force of morality - in other words, why we should be moral at all - are far less straightforward. In dealing with these latter issues, a number of Enlightenment thinkers found a role for religion.

Locke, for example, thought that reason enables us to recognise the divine origin of moral rules, and hence the basis of moral obligation. Kant found an alternative derivation of the "do unto others" principle from practical reason, but ultimately conceded that morality makes no sense at all without God and immortality.

Coming later, and from a rather different angle, Friedrich Nietzsche, in Twilight of the Idols, derided those (mostly Anglophone) writers who thought that they could cling to the basic content of Christian morality while relinquishing the religious premises that provided that content and gave it its normative force.

To return to the general point, contra Pinker, many Enlightenment figures were not interested in undermining traditional religious ideas - God, the immortal soul, morality, the compatibility of faith and reason - but rather in providing them with a more secure foundation. Few would recognise his tendentious alignment of science with reason, his prioritization of scientific over all other forms of knowledge, and his positing of an opposition between science and religion.

Post hoc, ergo propter hoc

That Pinker has managed to get this so spectacularly wrong is not altogether surprising given that he rarely deigns to cite any of the relevant writings. In fact, most of the important Enlightenment thinkers receive little or no mention at all in the book.

If we put into the practice the counting and gathering of data that Pinker so enthusiastically recommends and apply them to his own book, the picture is revealing. Locke receives a meagre two mentions in passing. Voltaire clocks up a modest six references with Spinoza coming in at a dozen. Kant does best of all, with a grand total of twenty-five (including references). Astonishingly, Diderot rates only two mentions (again in passing) and D'Alembert does not trouble the scorers. Most of these mentions occur in long lists. Pinker refers to himself over 180 times.

The first part of Pinker's book purports to deal with the historical Enlightenment. The two sections that follow are essentially non-sequiturs. In section two we encounter the promised data, presented in graphs. These are designed to demonstrate progress, and indeed many of them do, assuming the validity of Pinker's understanding of what it is that progress consists in. Much of the information presented here is genuinely interesting and it would be perverse to deny that many features of our contemporary world represent dramatic improvements over the past. What is less clear is what any of this has to do with the Enlightenment, even if we accept Pinker's view of it.

Here we run up against the fact that historical causation is notoriously difficult to establish. Too many variables. No prospects for double blind experiments. Little chance of deploying questionable statistical methods. Hence all the close reading, the teasing out of different lines of interpretation and the relative dearth of graphs.

Pinker never seems to see the force of the question: How do we know that all this did not take place in spite of, rather than because of, the Enlightenment? In fact, he doesn't even pretend to go to the trouble of establishing a causal connection between his contentious version of the Enlightenment and the various improvements that he imagines follow in its wake. Post hoc, ergo propter hoc seems to be the operative principle.

For the sceptical reader the whole strategy of the book looks like this. Take a highly selective, historically contentious and anachronistic view of the Enlightenment. Don't be too scrupulous in surveying the range of positions held by Enlightenment thinkers - just attribute your own views to them all. Find a great many things that happened after the Enlightenment that you really like. Illustrate these with graphs. Repeat. Attribute all these good things your version of the Enlightenment. Conclude that we should emulate this Enlightenment if we want the trend lines to keep heading in the right direction. If challenged at any point, do not mount a counter-argument that appeals to actual history, but choose one of the following labels for your critic: religious reactionary, delusional romantic, relativist, postmodernist, paid up member of the Foucault fan club.

For their part, historians have found the task of tracing the legacy of the Enlightenment more difficult, not least because even characterising what the Enlightenment was has proven challenging. It is now commonplace to speak of multiple Enlightenments and hence multiple and sometime conflicting legacies. Obviously, moreover, not everything that came after the Enlightenment has been sweetness and, well, light. Edmund Burke and G.W.F. Hegel, for example, drew direct connexions between the French Enlightenment and the reign of terror. In the twentieth century the German-Jewish philosophers Theodor Adorno and Max Horkheimer described what they called "the dialectic of Enlightenment" - a mixed inheritance that included the technical mastery of nature along with a conspicuous absence of the moral insights that would prevent that mastery being turned to barbarous ends. In their view, this led ultimately to the horrors of Nazism.

Pinker has not thought it worth his while to engage with these alternatives. (Burke is mentioned twice; Adorno and Horkheimer once, in a list of enemies of the Enlightenment.)

As well as a failure to engage seriously with alternatives to his rosy view of the past, Pinker's history suffers from a generic problem that often afflicts social scientific incursions into the sphere of the humanities, and that is a failure to see that what are considered to be the basic units of analysis - in this case "reason," "the Enlightenment," "religion" - are not natural kinds or simple, atomic, objects. Accordingly, they can be neither the subjects of simple explanation, nor can they themselves function as units of historical explanation. These things are complex historical products, and cannot be understood otherwise. Pinker essentially operates with implicit stipulative definitions of all three, with their mutual relations already built in. Having thus set things up, his history is really just a matter of cranking the handle.

Pinker's Providential Faith

A final remarkable feature of Pinker's vision is his teleological view of history - the idea that historical events are destined to unfold inexorably in a single direction. This is perhaps the only instance where he has genuinely succeeded in emulating what a good number of Enlightenment thinkers actually believed. This conviction is manifested not only in the downplaying of the horrors of much twentieth-century history, but in his touching faith that nothing will reverse the trend lines repetitively and graphically illustrated in the second part of the book.

Pinker seems to operate on the principle, for example, that future catastrophic events are impossible. The ultimate import of his graphs is to demonstrate some kind of inexorable and progressive historical law (although he doesn't admit as much). In Pinker's history, it seems as though there are no real contingencies - no prospect that the battle of Britain might had been lost, no prospect that the cold war might have turned into nuclear catastrophe, and for the future, no real sense of a potential calamity produced by climate change or a trigger-happy Kim Jong-Un (or his U.S. counterpart, for that matter). This is an almost providential view of history.

Partly for this reason, the book will no doubt attract a large audience. It is not just Steven Pinker and a goodly proportion of beauty pageant contestants who want world peace, progress and material prosperity. At some level, and with variations, this is what we all want. To be told that these are permanently underwritten by a historical trajectory that springs from the Enlightenment will no doubt be reassuring to some, particularly if the cost of maintaining the trend is a relatively painless subscription to the ideals of reason, science, humanism and progress.

For those sceptical of Pinker's imagined history and unconvinced by his sanguine assessment of human nature, the future is somewhat less certain. Achieving his desiderata, if possible at all, is likely to be hard work. And if history is to serve as any kind of guide in our efforts, we need to try to get it right and resist the temptation to reconstruct it in our own image.

Finally, and for reasons that I hope are now obvious, if Enlightenment Now is a model of what Pinker's advice to humanities scholars looks like when put into practice, I'm happy to keep ignoring it.

Peter Harrison is an Australian Laureate Fellow and Director of the Institute for Advanced Studies in the Humanities, University of Queensland.