It is needless to say that such a temper was constantly abused. Three-fourths of Diderot’s life were reckoned by his family to have been given up to people who had need of his purse, his knowledge, or his good offices. His daughter compares his library to a shop crowded by a succession of customers, but the customers took whatever wares they sought, not by purchase, but by way of free gift. Luckily for Diderot, he was thus generous by temperament, and not because he expected gratitude. Any necessitous knave with the gift of tears and the mask of sensibility could dupe and prey upon him. In one case he had taken a great deal of trouble for one of these needy and importunate clients; had given him money and advice, and had devoted much time to serve him. At the end of their last interview Diderot escorts his departing friend to the head of the staircase. The grateful client then asks him whether he knows natural history. “Well, not much,” Diderot replies; “I know an aloe from a lettuce, and a pigeon from a humming-bird.” “Do you know about the Formica leo? No? Well, it is a little insect that is wonderfully industrious; it hollows out in the ground a hole shaped like a funnel, it covers the surface with a light fine sand, it attracts other insects, it takes them, it sucks them dry, and then it says to them, ‘M. Diderot, I have the honour to wish you good day.’"[13]
Yet insolence and ingratitude made no difference to Diderot. His ear always remained as open to every tale of distress, his sensibility always as quickly touched, his time, money, and service always as profusely bestowed. I know not whether to say that this was made more, or that it was made less, of a virtue by his excess of tolerance for social castaways and reprobates. Our rough mode of branding a man as bad revolted him. The common appetite for constituting ourselves public prosecutors for the universe, was to him one of the worst of human weaknesses. “You know,” he used to say, “all the impetuosity of the passions; you have weighed all circumstance in your everlasting balance; you pass sentence on the goodness or the badness of creatures;