  The facts that there is a lot of collective action even in many large-number contexts in which the individuals do not have rich relationships with each other and that, therefore, many people are not free riding in relevant contexts suggest at least three possibilities. First, there are ways to affect the incentives of group members to make it their interest to contribute. Second, motivations other than self-interest may be in play. Third, the actors in the seemingly successful collective actions fail to understand their own interests. Each of these possibilities is important and interesting, and the latter two are philosophically interesting. Each is also supported by extensive empirical evidence.