Human Rationality in an Evolutionary Perspective
Dan Sperber

For any item that has a function, one can ask: How well does it perform its function? In other terms any such item can be evaluated normatively. What then is norm in terms of which one can evaluate cognitive mechanisms the function of which is to perform inferences? It is, I will argue, a norm of rationality in a broad sense. Inferential mechanisms are evolved in all animals that locomote, and hence rationality in this sense is not typically human, but, of course, it applies to human inferential mechanisms as well. Reasons, I will argue, play no role in rationality in this first sense.
Humans draw inferences about reasons. In The Enigma of Reason, Hugo Mercier and I have argued that inferences about reasons has two overlapping functions, to produce and evaluate justifications, and to produce and evaluate arguments. The reasons produced as justification or argument are evaluated in term of rationality in a second, narrower and more traditional sense of the term. I will describe this properly human notion of rationality, argue that it is intrinsically social, and discuss its relationship to rationality in the broader cognitive sense of the term.

Morality as Collective Rationality
Ralph Wedgwood

Just as we can make sense of what it is rational for an individual to do, we can also make sense of what it is rational for a group or a collective agent to do. In the relevant sense, to be a collective agent, a group does not need to be formally constituted (by institutional structures, such as laws or explicit social rules or the like). It is enough if the individuals constituting the group have some awareness of what other members of the group are doing, and adjust their actions in the light of that awareness. In the largest sense of the term, for any agent to act or to think rationally is for the agent to act as it has most reason, all things considered, to act to think. The goal of this discussion is to explore a certain hypothesis, which implies that there is a fundamental connection between collective rationality and morality. According to this hypothesis, the two fundamental demands of morality are: (i) that we play our part in the collectively rational activities that we are already engaged in; and (ii) that we try as much as possible to transform our interactions with other agents into collectively rational activities. By relying on this fundamental connection between them, we can illuminate both morality and collective rationality. We can start out from intuitively plausible principles about morality to illuminate the conditions under which a group’s activities are collectively rational; and conversely, we can start out from intuitively plausible principles about collective rationality to illuminate the requirements of morality.