This volume is made up of lessons on character psychology. In them the author intends to explain how human societies work, and for this established and described three types of characters that he claimed exist in any community of human beings: the idealist, the mediocre man, and the inferior man. Ingenieros did not hide his admiration for the first type but, beyond moral judgments, made the effort to understand the psychological perspective and particularities of each type and its specific role in our societies. He devoted a major part of the work to the second type, the mediocre man, because it constitutes the bulk of society.