A C Grayling
Great Minds Don't Think Alike
Rousseau's Dog
By David Edmonds and John Eidinow (Faber & Faber 405pp £15.99)
The Courtier and the Heretic
By Matthew Stewart (Yale 405pp £16.99)

It should be acknowledged as a universal truth that if one person helps another, the latter will forever resent the former, because it is uncomfortable to be in moral debt. The only way to avoid this outcome is for help to be recompensed, either by a return of favours or – better far – by an undertaking from the helpee to find an opportunity to help someone else in future, thus passing onward the good deed.

The universal truth at the hub of these remarks is well illustrated by the case of the quarrel between that unpleasant, egomaniacal, paranoid, toxic, ghastly genius Jean-Jacques Rousseau, and that unimpeachable man of reason, amenity, civilisation, and yet greater genius, David Hume. As the epithets here suggest, I am of the opposite view to that taken by David Edmonds and John Eidinow in their wonderfully readable and absorbing account of the unfortunate transactions between these two eighteenth-century savants. They eccentrically favour Rousseau’s side of the tale, which in one way scarcely matters because they tell the tale so well, providing in their comprehensive and lucid way a full background to the Enlightenment world and the place of these two seminal thinkers in it.

The story is as follows. After annoying everyone from the authorities to those who attempted to be his friends, the former by his writings and the latter by his typically nauseating self-obsessed behaviour, Rousseau had nowhere left to run and hide. Hume, who had just completed a two-year stint as Secretary to the British Embassy in Paris, where he had been lionised and loved by Parisian salon society, offered to take Rousseau – though not knowing him personally – to sanctuary in England, there to find him a home and secure him a pension from the King. Rousseau obligingly allowed himself to be rescued and housed. But within a very short time he was accusing Hume of plotting against his reputation, and aiding those who (justifiably enough) made fun of Rousseau’s rebarbative and generally unpleasant personality.

Hume certainly found Rousseau extremely tiresome. One knows people like Rousseau (less gifted, no doubt; but in these cases gifts ameliorate nothing), and therefore knows exactly why Hume practised little deceptions – like not telling Rousseau that someone was subsidising his travel expenses, because of the fuss that would result from the Genevan ingrate’s inflated and prickly pride. From this white deception, indeed, flowed the huge outburst of the quarrel between them, the degree of Rousseau’s toxicity being measurable by the uncharacteristic annoyance shown by Hume in response.

Edmonds and Eidinow inexplicably take Rousseau's side, against all the background evidence of the two men's personalities and histories, and by dint of not seeing how a man like Rousseau could invite the dislike, indeed the contempt, even of those who acknowledged his intellectual and literary powers.

This was especially so with those who made efforts to help him. Rousseau left all of his many children, as new-borns, on the doorstep of the Foundling Hospital, and then wrote a book about the education of the young; such was the man. Hume was an atheist and on his deathbed cheerfully acknowledged as much to the aghast Boswell; no inconsistency there. Who would you think likelier to be right in a quarrel started by Rousseau's paranoia and self-obsession?

Otherwise Edmonds and Eidinow have produced a highly enjoyable book, richly informative and entertaining, written with easy lucidity and obvious relish.

Matthew Stewart's account of the relationship and differences between two immense philosophical intellects of the seventeenth century, Baruch Spinoza and Gottfried Leibniz, is gripping. Because the former lived an exiled, impoverished, solitary life that kept unwaveringly true to the principles on which it was based, and because the latter was a socially-conscious, ambitious, temporising and worldly man, Stewart's sympathies run with the former.

One admires Spinoza for these among many other reasons and not least the sheer power of his thought – but one also understands Leibniz, if only because he sincerely (and Stewart acknowledges this) thought that by succeeding in the world he could help it to be a better place.

Spinoza has lately come into his own in intellectual history as one of the true begetters of the Enlightenment that flowered in the century after his own. His extraordinary mind and the rigour of his thought were for a long time insufficiently celebrated because he was demonised as an atheist, a heretic and a subversive influence. Leibniz, by contrast, has occupied more of the sunshine of the world's regard since his own day, and it remains a point of admiration that his voluminous writings, containing the far-flung reach of his polymathic genius, have still not been fully edited and published.

But even as Leibniz wrote to others in denigrating terms of Spinoza as the Jew atheist, he was writing in far different terms to Spinoza himself. Genius recognises its equal. He visited Spinoza, and they talked; their subject was God, and Leibniz tried to get Spinoza to accept a proof of the deity's existence. It is likely that in most respects the mutual imperviousness of great minds operated here as it almost always does, and so the encounter between these two extraordinary and very different men, with their very different metaphysics, was not calculated to bring about agreement. But at least they met, and the fact itself is a fascinating one.

This hook gives Stewart his opportunity to provide the best current untechnical introduction to the lives and philosophies of the two men. He does it in very agreeable prose, and what he says rests on a sound bottom of historical and philosophical scholarship, so lightly worn that one is not conscious of the skill that has gone into making the epoch and its seminal ideas accessible. The result is a thoroughly good book, hard to put down for anyone interested in the great story of the Western intellectual tradition.