Abstract

This paper takes as its starting point the problem of characterizing, in a precise way, situations in which two people collaborate to achieve a common goal. It is suggested that collaboration is normally based on an apparently paradoxical state of mind which I call “mutual intention”. Mutual intention is a concept belonging to the same family as Lewis's and Schiffer's “mutual knowledge”. These concepts have the paradoxical feature that they require, for their definition, an infinite series of propositions of the form X knows p, where X is a single agent and p is a proposition. The source of these infinite series is traced, and it is shown that they can be represented in a plausible and enlightening way by means of a recursive notation. Finally, three applications of the concept of “mutual intention” are given: in the semantic analysis of certain sentences with plural subjects; in the analysis of agreement and related speech acts; and in the clarification of the phenomenon of “implicit agreement”