For people to contribute to discourse, they must do more than utter the right sentence at the right time. The basic requirement is that they add to their common ground in an orderly way. To do this, we argue, they try to establish for each utterance the mutual belief that the addressees have understood what the speaker meant well enough for current purposes. This is accomplished by the collective actions of the current contributor and his or her partners, and these (...) result in units of conversation called contributions. We present a model of contributions and show how it accounts for a variety of features of everyday conversations. (shrink)

What is involved when a group of agents decide to do something together? Joint action by a team appears to involve more than just the union of simultaneous individual actions, even when those actions are coordinated. We would not say that there is any teamwork involved in ordinary automobile traffic, even though the drivers act simultaneously and are coordinated (one hopes) by the traffic signs and rules of the road. But when a group of drivers decide to do something together, (...) such as driving somewhere as a convoy, it appears that the group acts more like a single agent with beliefs, goals, and intentions of its own, over and above the individual ones. [more]. (shrink)

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”. (shrink)

The work of Tversky, Kahneman and others suggests that people often make use of cognitive heuristics such as availability, salience and representativeness in their reasoning and decision making. Through use of a historical example--the recent plate tectonics revolution in geology--I argue that such heuristics play a crucial role in scientific decision making also. I suggest how these heuristics are to be considered, along with noncognitive factors (such as motivation and social structures) when drawing historical and epistemological conclusions. The normative perspective (...) is community-wide, contextual, and instrumental. (shrink)