An Enquiry concerning the Principles of Morals, first published in 1751, was the third of David Hume's major philosophical treatises. Hume's aim in this elegant and lucid work was to present in an accessible way his theory of the foundation of morality in human nature, a theory which had developed significantly since he first addressed the subject in A Treatise of Human Nature (1739-40). He considered this Enquiry to be 'of all my writings, historical, philosophical, or literary, incomparably the best'.