In this paper, we present a social model for software agent conversa-tions for action based on social commitments and their negotiation. We depart from the premises that conversations are cornerstone to support autonomous and heterogeneous agents, and that conversational coherence can be supported through public definitions of speech act and compositional semantics. We specify a unified social model for conversations in which speech act seman-tics is an emergent product of identity, conversational use, and potential conse-quences, and where conversational composition is guided by rules of conversa-tional use and their application to the state of conversation instances. Lastly, we show the effectiveness of this novel approach by formally describing the evolution of a simple conversation for action.