Of his many books, Crystallizing Public Opinion (1923) and Propaganda (1928) gained special attention as early efforts to define and theorize the field of public relations. Citing works of writers such as Gustave Le Bon, Wilfred Trotter, Walter Lippmann, and Sigmund Freud (his own double uncle), he described the masses as irrational and subject to herd instinct—and he outlined how skilled practitioners could use crowd psychology and psychoanalysis to control them in desired ways.