Possible-World and Multiple-Context Semantics for Common-Sense Action Planning Maria J. Santofimia a , Scott E. Fahlman b Xavier del Toro c and Francisco Moya a Juan C. Lopez a a Computer Architecture and Network Group. University of Castilla-La Mancha b Carnegie Mellon University c School of Industrial Engineering. University of Castilla-La Mancha Abstract. Event management and response generation are two essential aspects of systems for Ambient Intelligence. In this regard, the context notion does also play an essential role, not only in determining the set of activities that take place in it, but also in devising the most appropriate response to those situations. Context is also essential for disambiguating knowledge and meaning. This work therefore proposes handling these issues by means of an approach with which to model and reason about actions and events which, under the umbrella of a philosophical and common-sense point of view, describes what actions and events are, how they are connected, and how computational systems should consider their meaning. Actions and events occur in the frame of situations. In order to leverage Ambient Intelli- gence systems to autonomously manage their environment these situations need to be characterized and understood. This work also describe an approach to tackle this challenge. Keywords. Common sense, Ambient Intelligence, Context model Introduction The notion of context is at the heart of the Ambient Intelligence paradigm because of its role in narrowing down the meaning of the environmental events and in determining suitable means to react to undesired situations. Despite the importance of context, this concept has not yet been universally formalized. On the contrary, the fact that the notion of context is a relevant issue for different fields of knowledge such as natural language understanding, linguistics, context-awareness, or knowledge representation among some, makes it difficult to provide a common and unique definition of what context is. Some authors such as McCarthy [33] echo this peculiarity, deciding not to offer a definition of context since, under their perspective, it is as pointless as asking about the definition of a group elements [2]. Rather than trying to provide a definition of context, John Sowa in [46] distinguishes three different functions for the notion of context, as known: collecting the syntax of a given context; semantically mapping linguistics to physical situations; and pragmatically