We sometimes speak of it as a phenomenon unique to the Internet era: You befriend a virtual acquaintance in a chat room or on a bulletin board. You have shared interests, similar complaints and you both have a facility with the written word. Then you meet in meatspace, and it turns out your high-minded friend is socially inept, abrasive, cold or emotionally fragile. Face-to-face, you hear imagined insults and whispered conspiracies. You return to your keyboards and burn billions of bits in a flame war that diminishes you both.
The medium was different in the era of salons and snail mail, but this is basically what happened between the Genevan philosopher and political theorist Jean-Jacques Rousseau and the rotund Scottish philosopher and historian David Hume, as told by David Edmonds and John Eidinow in Rousseau's Dog. Writing in the mid-18th century, both Rousseau and Hume critiqued the Enlightenment's faith in reason as the method to all understanding and the means for all human progress. Both ran afoul of Christian leaders for critiquing religious beliefs.
In Rousseau's hour of need, when he had been serially exiled from several sanctuaries in Continental Europe, Hume came to his rescue, bringing Rousseau to London and looking after him. For a brief moment, they were fast friends.
There would be great scholarly satisfaction in finding that their subsequent battle broke out over a fine point of philosophy; Rousseau's and Hume's answers to the limitations of reason were dramatically different. But reason seems to have had little to do with the mutual smear campaign they fought through open letters and pamphlets. (No, they never dueled. Philosopher flamers, not fierce feuders, after all.)
They seem instead to have had a clash of temperaments, albeit temperaments well suited to their respective philosophies. Rousseau was fragile, manic and paranoid, with a deep aversion to the slightest hint of dependence on another human being: an outgrowth of his radical egalitarianism and an almost impossible standard for an exile to keep. Hume was reserved but generous, dedicated to fulfilling his obligations as a civilized man. Hume offered help but withheld his heart, an imbalance in which Rousseau was predisposed to see conspiracy.
Edmonds and Eidinow blend clear intellectual history with tabloid-worthy gossip in their telling of the two men's flame war. There is inevitably a persistent note of middle school scandal mongering to the book, though nothing these perhaps too successful critics of reason don't richly deserve.