The importance of defining a standard framework for agent communication languages (ACL) with a simple, clear, and a verifiable semantics has been widely recognized. This paper proposes a logic-based semantics which is social in nature. The basic idea is to associate with each speech act a meaning in terms of the commitment induced by that speech act, and the penalty to be paid in case that commitment is violated. A violation criterion based on the existence of arguments is then defined per speech act. Moreover, we show that the proposed semantics satisfies some key properties that ensure the approach is well-founded. The logical setting makes the semantics verifiable.