In the title to the second section of Book 3 Hume announces that “Moral distinctions [are] deriv'd from a moral sense” (T3.1.2).The phrase “moral sense” is taken from the philosophies of Francis Hutcheson and Lord Shaftesbury, whose writings Hume had clearly studied very carefully as he was writing Book 3 of the Treatise. However, apart from the title to this section, Hume uses the phrase “moral sense” only one other time in the Treatise, in Book 3, Part 3, where he claims to give his own “explication of the moral sense” (T3.3.1.25: 588). It is never used in his later recasting of his moral theory in the Enquiry Concerning the Principles of Morals. It is true that later in Book 3 of the Treatise he does sometimes use the phrase “sense of morals.” But in the Conclusion to Book 3 of the Treatise he contrasts his own account of the “sense of morals” with the account of “those who resolve the sense of morals into original instincts of the human mind” – an apparent reference to the theory of moral sense of Hutcheson (T3.3.6.3: 619). His own view, he tells us, accounts “for that sense by an extensive sympathy with mankind.”

As we have seen in Chapter 1, Hume's personal relations with Hutcheson, which began as he was revising Book 3 for publication, were complex. Hume sought Hutcheson out as an authority who would recommend his philosophy to others.