Robert Michels left his iron law of oligarchy undefined, and Cassinelli sets out to make it statable before anyone judges it. He supplies the two missing definitions. An organization becomes a group of human activities ordered by specialization of function, with a subgroup whose goal is maintaining that order; taking cues from Chester Barnard and Max Weber, he builds it from activities rather than persons, so that turnover, dual membership and short-lived bodies all fit. Of five readings the law might carry, he adopts the fourth: the activities holding most authority escape control by the subordinate ones, which yields a theory of irresponsible leadership. Michels's technical causes, sheer numbers, the volume of decisions and the need for experts and professionals, carry the explanation, while the psychological causes about apathy and gratitude belong to any large group. The law applies only above a membership between one thousand and ten thousand, and says nothing about whole societies.