Formal theories of multi-agent systems require a rich ontology for modelling the dynamics of social behaviour. In this paper a formal analysis of the social behaviour of individual and social agents within the BDI paradigm is provided. The central idea behind this approach is that stability and regulation of activity within a group of agents can be accounted for by means of a complex web of roles, commitments obligations and rights. In particular, collective commitments are considered to be the attitudes that hold a group of agents together. In pursuit of their own objectives as well as in order to support their collective commitments, agents adopt roles and undertake social commitments. Being semi-autonomous they may decide to drop their commitments and roles, but they may have to bear the consequences of the other agents’ prerogative to exercise their rights. Categories and Subject Descriptors I.2.11 [Arti…cial Intelligence]: Distributed Arti…cial Intelligence—Multiagent sys...