Divided into three books, this work draws together the concerns of many of author's works. The first book presents author's version of the "four-stage theory of history". The second book explores the implications of natural 'appetite for society'. The final book presents an account of progress in the sciences of logic, morals, and theology.

In the final book, Kames turns to an account of progress in the sciences of logic, morals, and theology. He seeks to vindicate the claim that "human understanding is in a progress towards maturity, however slow". Throughout the entire work, Kames expounds on his fundamental hypothesis that at the beginning of the history of the human race, savagery was ubiquitous and that the human story is one of an emergence out of barbarism and toward maturity.