This paper is mainly about cooperation as a collective action in a group context (acting in a position or participating in the performance of a group task, etc.), although the assumption of the presence of a group context is not made in all parts of the paper. The paper clarifies what acting as a group member involves, and it analytically characterizes the ‘‘we-mode’’ (thinking and acting as a group member) and the ‘‘I-mode’’ (thinking and acting as a private person).