In this work, Homans also proposes that social reality should be described at three levels: social events, customs, and analytical hypotheses that describe the processes by which customs arise and are maintained or changed. Hypotheses are formulated in terms of relationships among variables such as frequency of interaction, similarity of activities, intensity of sentiment, and conformity to norms. Using notable sociological and anthropological field studies as the grounding for such general ideas, the book makes a persuasive case for treating groups as social systems that can be analyzed in terms of a verbal analogue of the mathematical method of studying equilibrium and stability of systems. In his theoretical analyses of these groups, he begins to use ideas that later loomed large in his work, e.g., reinforcement and exchange. Along the way, he treats important general phenomena such as social control, authority, reciprocity, and ritual.