Smith’s argument is that human morality is a social system that arises—like languages, like ecosystems, and like markets—on the basis of countless individual decisions, actions, and interactions but without any overall plan and with no overall designer. Each of us begins life with no moral sentiments whatsoever, but with an instinctive desire for mutual sympathy of sentiments. Interactions with others—and, in particular, experiences in which others judge us—trigger our desire for mutual sympathy of sentiments and begin the lifelong process of finding ways to behave that stand a chance of achieving this sympathy, which Smith believes is, along with the desire to procreate, among the strongest social desires humans have. This trial-and-error process, which we conduct with others who similarly wish to achieve mutual sympathy, leads us to develop habits of behavior that reflect successful attempts. These habits eventually become, through suitable refinement, principles of behavior, and then come to inform our conscience. Because we develop these principles with others in our community, they can become a shared system of moral judgment
Otteson’s book and related media can be freely explored here.