Abstract

There exist many competing philosophical definitions of joint action and no clear criteria to decide between them; so far the search for definitions has by and large been a semantical enterprise rather than an empirical one. This chapter describes and assesses several constraints that could help converge towards a set of necessary and sufficient conditions for joint action. The tightness constraint favours definitions that fit joint actions in which the links between agents are as relaxed as possible, so as to better pinpoint the conceptual core of jointness. The developmental constraint asks for definitions based on realistic psychological states that could be entertained by agents less cognitively developed than ideal human beings. The motor constraint holds that definitions should refer to psychological mechanisms involved in actual human coordination. These first three constraints are discussed and dismissed, mainly because they manage to establish vague limits at best (for various reasons). I then introduce a fourth one, the efficiency constraint, based on the fact that most of our joint actions are generally successful, and according to which definitions should involve conditions that help justify this success. Finally, the rational and evolutionary versions of the efficiency constraint are examined and defended against objections.