System and Process (1957) broke the mould in political science by combining systems, game, and cybernetic concepts in its theoretical formulations. Since its publication, serious research in international relations has needed to respond to the bold hypotheses that matched equilibrial rules with type of system. Kaplan's life-long interest in finding an objective basis for moral judgments had its scholarly origins in an appendix of this classical book, which incorporated his understanding of philosophy and, in particular, the philosophy of science. A second appendix on 'The Mechanisms of Regulation' explored the cybernetic and recursive nature of knowing.