What was the Enlightenment? Damned if I know. There have been so many books devoted to that question in recent years that it would be churlish to venture a definitive answer. Anyone who has dared to keep up with the literature in this field will have read about radical Enlightenments and moderate Enlightenments; contested, clandestine and cosmopolitan Enlightenments. The era of Enlightenment has been claimed by some as a beacon of tolerance, democracy and secularism; it has been denounced by others as a cesspit of persecution, authoritarianism and imperialism. As concepts go, Enlightenment has proved singularly flexible. If one were to judge by book titles alone (sometimes more satisfying than wading through the latest thousand-page tome, and certainly quicker) all one would know for certain is that the Enlightenment somehow made the modern world, though one would be forgiven for not knowing precisely how that was supposed to have happened.

The great danger of assuming the Enlightenment made the modern world is that it tends to receive the credit for all that is good about modernity as well as the blame for all that is bad. And yet, as Richard Whatmore reminds us in his powerful and meticulously argued new book, ‘sometimes the present prevents us from understanding the past’. We risk thinking that the philosophers of the 18th century were answering our questions instead of their own, when in fact it is the fundamental weirdness of their ideas that makes them so interesting. It is also this inherent strangeness that, as Whatmore demonstrates beyond all doubt, makes their recovery so vital for present times.

Whatmore’s book, which is a substantially revised and expanded version of his Carlyle Lectures delivered at Oxford in 2018, approaches the Enlightenment on its own terms. When Hume and his contemporaries challenged religious superstition, zeal and bigotry, their aim was not the cultivation of individual flourishing so much as providing a framework for advancing and maintaining civil peace. For more than 200 years, Europe and its nations had been ravaged by international and internecine wars of religion. Conflict was fuelled by fanaticism, and fanaticism by superstition. Moderation, toleration and democracy were therefore part of the Enlightenment toolkit for abolishing war and empire in perpetuity. So too were industry, commerce and free trade.

By the end of the 18th century, however, the Enlightenment dream had become a nightmare. On the Continent, as Whatmore puts it, ‘revolutions initiated to restore liberty and reason themselves unleashed intolerance and the justification of terror’. Religious superstition was replaced by political enthusiasm. In Britain, deeply entrenched anti-Catholicism morphed into Francophobia and a new kind of hot-blooded warmongering patriotism. Meanwhile, lust for empire corroded the national psyche, leading to luxury, vice and corruption. Trade wars stretched from the English Channel to the farthest-flung corners of the globe. The Enlightenment was intended to achieve peace on Earth. Instead it ended in bloodshed.

How did the philosophers get it so hopelessly wrong? Whatmore rightly devotes much attention to how badly they underestimated the capacity of corrupt mercantile systems to sustain themselves through empire and war. Writers in the 18th century liked to speak of ‘the pursuit of happiness’, but in Whatmore’s bleak vision ‘happiness’ translates merely to ‘the ever-growing consumption of luxury goods’. Merchants used violent means to secure the foreign resources necessary to feed this domestic appetite. But the real kicker was a fundamental naivety regarding human nature. Hume and his acolytes had not counted on the translation of superstition and intolerance from religion into politics. Just as soon as people stopped being willing to kill and die for their religion, they started killing and dying for their country. Human beings are naturally violent creatures, simultaneously suspicious of difference and – shock horror – perfectly content to live within oppressive systems that provide some degree of affluence. Material comfort wins every time.

Whatmore’s book is structured around eight chapters, each of them focused on a different Enlightenment thinker, plus two broader themed chapters which open and close the volume. We begin with Hume, an embittered 60-something grumbling about the world having gone to the dogs, and end with Wollstonecraft, trying to make sense of how the French Revolution crumbled into a humanitarian catastrophe. It would be tempting to read into the generational difference between those thinkers who lost faith in the Enlightenment idea and those for whom the fires of equality and toleration never lost their heat were it not for the curious coincidence that Edward Gibbon and Thomas Paine – it is difficult to imagine two more temperamentally different writers – were born within months of one another.

As a historian, Whatmore is more of an ideas man than a truffle hunter (readers will search in vain for any reference to a manuscript in the gratuitous 120 pages of endnotes). There is, however, buried treasure in his account of how figures from different intellectual backgrounds negotiated the Enlightenment crisis: not by doubling down on ill-founded convictions, but by returning to their desks and studying the past. A final, moving paragraph lists half a dozen Jewish scholars who, having survived the Holocaust, devoted their remaining days to understanding the intellectual culture of the 18th century. ‘Rather than turning against European history, they sought lessons for the present in the history of fanaticism and the strategies of enlightenment that were formulated to prevent it.’ Whatmore is to be applauded for following their example.

• The End of Enlightenment: Empire, Commerce, Crisis 
  Richard Whatmore 
  Allen Lane, 496pp, £30
  Buy from bookshop.org (affiliate link)

Joseph Hone’s latest book The Book Forger: The True Story of a Literary Crime that Fooled the World will be published by Chatto & Windus in March 2024.