This study looks at three of the most basic elements of criminal liability: when does a person "act"? When do his acts fall within the prohibitions of criminal law? And when do his acts overlap sufficiently that he may be prosecuted or punished only once for them?

Introduction - criminal law's three conduct requirements. Part 1 Basic acts and the act requirement: the doctrinal unity of the act requirement; the orthodox view of the act requirement and its normative defence; the metaphysics of basic acts I - the existence of actions; the metaphysics of basics acts II - the identity of actions with bodily movements; the metaphysics of basic acts III - volitions as the essential source of actions. Part 2 Complex action descriptions and the "actus reus" requirement: the doctrinal basis of the "actus reus" requirement; unity in complex action description and in the "actus reus" requirement; the normative basis for the "actus reus" requirement; the metaphysiss of complex actions I - the dependence of complex actions on basic acts; the metaphysics of complex actions II - the identity of complex actions with basic acts. Part 3 The identity conditions of actions and the double-jeopardy requirement; the doctrinal and normative basis of the double-jeopardy requirement; legal, moral and metaphysical notions of the "sameness" of action-types; legal, moral and metaphysical notions of the "sameness" of act-tokens.