This course examines what it means to be 'rational' in negotiating the world and conducting one's life. At issue is the quality of one’s beliefs, desires and choices about how to act, particularly in the face of uncertainty, and in concert with others.

Part I is a critical examination of the standard theory of individual rationality - expected utility theory – that unites and explicates the aforementioned key mental attitudes. This theory stems from the classic work of philosophers/social scientists such as Ramsey, de Finetti and Savage. Contemporary challenges to the standard theory come from diverse directions, with some arguing that the theory is too little constrained and even vacuous, and others arguing that it is too rigid, either in its prescriptions for representing and handling uncertainty or else by virtue of being in conflict with some prominent ethical accounts of right action. The course considers these challenges to the standard theory and the responses/developments they have inspired.

Part II turns to rationality in a social context. One question is how collective judgments should depend on the judgments of the individual members. This question is pursued in the context of democratic theory, where the focus is on the procedure by which a group should decide on actions or attitudes to jointly adopt. This question is also pursued in the context of social welfare or choice theory, where the focus is on determining the collective preference ranking over social states that best represents, or is the most appropriate aggregate of, the respective individual preference rankings. A rather different sort of question is what an individual should do when the consequences of their choice depend on what others do, and vice versa. This is the province of game theory. Standard solution concepts for games are introduced, but the focus is on the limits of these solutions—when collective-action problems arise. Bargaining theory is introduced as a way of negotiating these collective-action problems (amongst other sorts of problems); it may be seen as an intermediary between game theory and social welfare or choice theory.