Introduction to Contextual Reasoning. An Artificial Intelligence Perspective

The notion of `context` is called to account for a multifarious variety of phenomena in philosophy of language, Artificial Intelligence (AI) and Cognitive Science. The motivations and the approaches to the problem of context are very different, and one might even wonder whether there is something as `the` probalem of context, or rather a multiplicity of different problems very loosely related by the word `context`. We will argue that most of the proposed notions of context can be looked at from a unifying perspective. However, before we are ready to defend this claim, a lot of preliminary work is needed. This paper mostly addresses the following (rather philosophical) questions: what is context? What does it mean for a representation to depend upon context? Is context an essential aspect of a theory of knowledge representation? Can we get by without context? The structure of this paper is the following. In the first part of the paper we argue that the notions of context proposed in the literature relies on two very different intuitions. According to the first, a context is thought of as a part of the structure of the world; according to the second, a context is thought of as a part of the structure of an individual`s representation of the world. We call the resulting notions of context `pragmatic context` and `cognitive context` respectively, in the literature on context, thought of in two different ways. In the second part of the paper we shaw that, from the standpoint of a theory of knowledge representation, the notion of pragmatic context can be eliminated in favour of the notion of cognitive context, and that the latter is an essential building block in any teory of knowledge representation. This will be the starting point for some considerations on the place of context in a theory of knowledge representation. Finaly we introduce two basic principles of contextual reasoning, namely `locality` and `compatibility`