 As the title of the Treatise proclaims, Hume’s subject is human nature. He summarizes his project in its subtitle: “an attempt to introduce the experimental method into moral subjects”. In his day, “moral” meant anything concerned with human nature, not just ethics, as he makes clear at the beginning of the first Enquiry, where he defines “moral philosophy” as “the science of human nature” (EHU 1.1/5). Hume’s aim is to bring the scientific method to bear on the study of human nature.