William Graham Sumner begins by defining folkways as the unconscious, uncoordinated habits and customs that groups develop through trial and failure to satisfy basic needs like hunger, love, vanity, and fear. Over time, as these folkways acquire philosophical and ethical justifications concerning societal welfare, they evolve into mores. These mores exercise a powerful coercive and regulative force over every individual within a society, dictating right and wrong, truth, and the proper modes of behavior.
Throughout the work, Sumner emphasizes the immense inertia and rigidity of the mores. They are not created by human purpose or legislative design, but rather grow naturally like products of natural forces. Consequently, arbitrary attempts by rulers, reformers, or revolutionaries to alter them swiftly almost invariably fail or produce social chaos, because mores contain their own traditional authority and are deeply rooted in ancestry and ghost fear.
Ethnocentrism is identified as the universal view wherein one's own group is the center of everything, leading each society to view its own folkways as the only right ones while looking down on outsiders. This in-group solidarity and out-group hostility drive societal organization and discipline. Sumner illustrates how the aleatory element—good and ill luck—constantly influences human life philosophy, linking the struggle for existence with goblinism, magic, and early religious ritual.
The treatise explores how institutions such as property, marriage, and religion originate directly in the folkways and mores rather than from abstract philosophy or rational contract. Laws and positive enactments can only succeed when they remain consistent with the underlying mores of the people. Through extensive historical and ethnographical illustrations, Sumner demonstrates that the mores are the supreme directive force in history, dictating the rise and decline of civilizations, social classes, and human institutions.
