Abstract: The intuitive starting point of the book is the distinction between thinking and acting as a private person versus as a group member. People may view things from their own personal viewpoint and base their thinking and acting on this “I-perspective”. They can then be said to operate as private persons, in the I-mode, even when they are engaged in social action with others. Alternatively, they may adopt the perspective of their social group and view things from a full “we-perspective”, that is, from the group's point of view that is constituted and shared by its members. Then they can be said to operate in the we-mode. The most central thesis of the book is that collective intentionality is an essential ingredient in sociality and that especially we-mode collective intentionality is important. Social life and social institutions cannot be properly understood or explained in terms of I-mode concepts only, and in certain respects the we-mode can even be seen as primary when compared to the I-mode.The book develops a systematic theory of sociality giving special emphasis on phenomena of collective intentionality, such as joint intentions, collective commitment, collective action, and group beliefs. The theory is used to investigate such topics as social institutions, cooperation, cultural evolution, and group responsibility. We-mode intentionality is compared with various forms of I-mode intentionality, and it is argued that the we-mode is irreducible to the I-mode. Yet the present book defends a naturalistic view of the social world. Accordingly, it is argued that the we-mode is an adaptation based on the co-evolution of genetic and cultural factors.The present book offers new ideas and conceptual tools for philosophers and social scientists interested in the conceptual and philosophical foundations of social theorizing.

Keywords: acting as a group member,, collective acceptance,, collective commitment,, collective intentionality,, cooperation,, cultural evolution,, group attitude,, group reason,, group responsibility,, I-mode,, institutional status,, joint action,, joint intention,, social institution,, we-mode,, we-perspective