 Hume looms large in Russell’s Human Knowledge. Indeed the whole book can be seen as an attempt to concede the premises of Hume’s skeptical argument—that the data we start with are private and personal and that we cannot infer an external world from such data by means of demonstrative inference—whilst resisting its conclusion—that we can have no knowledge of an external world. (Hence the need for non-demonstrative inference.) But although Hume was Russell’s chief opponent in Human Knowledge, he was perhaps a meta-ethical ally in Human Society. In the Enquiry Concerning the Principles of Moral, Hume sought to base an inter-subjective ethic on human sentiments, specifically the sentiments of approbation and disapprobation. Hume was much more at ease in the world than Russell, and was only interested in moral reform in so far as morals rested on the “delusive glosses of superstition and false religion” (which in his opinion included all religion) or the ideological delusions of factious politicians and mercantile economists. But he did want a meta-ethic that would enable him to transfer the monkish virtues (whose status as virtues depended on the “delusive glosses”) from the catalogue of virtues to the catalogue of vices. Thus he wanted to be able to show that those who approved of “celibacy, fasting, penance, mortification, self-denial, humility, silence, solitude” were making some kind of mistake. How did he propose to do this? By combining a definition with an empirical research program.