This books is a masterpiece, not only of philosophical ethics, but also of social psychology. It recasts ethics by examining the psychology of why people think some actions good and other actions bad. It's examination of these psychological factors is both incisive and pretty exhaustive.
At times, it contains pre-echoes of the ideas of modern evolutionary psychologists, as in the following passage: "Thus self-preservation, and the propagation of the species, are the great ends which Nature seems to have proposed in the formation of all animals. Mankind are endowed with a desire of those ends, and an aversion to the contrary; with a love of life, and a dread of dissolution;… Read more