This symposium contains a selection of the papers that were presented at a conference we organized on Rational Choice and Philosophy that was held at Vanderbilt University on 16 and 17 May 2014. The aim of the conference was to provide an inter-disciplinary forum for philosophical work that uses ideas and tools from rational choice theory, understood broadly to include decision theory, game theory and social choice theory.

We introduce a ‘reason-based’ framework for explaining and predicting individual choices. The key idea is that a decision-maker focuses on some but not all properties of the options and chooses an option whose ‘motivationally salient’ properties he/she most prefers. Reason-based explanations can capture two kinds of context-dependent choice: (i) the motivationally salient properties may vary across choice contexts, and (ii) they may include ‘context-related’ properties, not just ‘intrinsic’ properties of the options. Our framework allows us to explain boundedly rational and sophisticated choice behaviour. Since properties can be recombined in new ways, it also offers resources for predicting choices in unobserved contexts.

What value should we put on our chances of obtaining a good? This paper argues that, contrary to the widely accepted theory of von Neumann and Morgenstern, the value of a chance of some good G may be a non-linear function of the value of G. In particular, chances may have diminishing marginal utility, a property that is termed chance uncertainty aversion. The hypothesis that agents are averse to uncertainy about chances explains a pattern of preferences often observed in the Ellsberg paradox. While these preferences have typically been taken to refute Bayesian decision theory, it is shown that chance risk aversion is perfectly compatible with it.

Behaviourism is the view that preferences, beliefs and other mental states in social-scientific theories are nothing but constructs re-describing people’s behaviour. Mentalism is the view that they capture real phenomena, on a par with the unobservables in science, such as electrons and electromagnetic fields. While behaviourism has gone out of fashion in psychology, it remains influential in economics, especially in ‘revealed preference’ theory. We defend mentalism in economics, construed as a positive science, and show that it fits best scientific practice. We distinguish mentalism from, and reject, the radical neuroeconomic view that behaviour should be explained in terms of brain processes, as distinct from mental states.

Preference-aggregation problems arise in various contexts. One such context, little explored by social choice theorists, is metaethical. ‘Ideal-advisor’ accounts, which have played a major role in metaethics, propose that moral facts are constituted by the idealized preferences of a community of advisors. Such accounts give rise to a preference-aggregation problem: namely, aggregating the advisors’ moral preferences. Do we have reason to believe that the advisors, albeit idealized, can still diverge in their rankings of a given set of alternatives? If so, what are the moral facts (in particular, the comparative moral goodness of the alternatives) when the advisors do diverge? These questions are investigated here using the tools of Arrovian social choice theory.

Juries, committees and experts panels commonly appraise things of one kind or another on the basis of grades awarded by several people. When everybody's grading thresholds are known to be the same, the results sometimes can be counted on to reflect the graders’ opinion. Otherwise, they often cannot. Under certain conditions, Arrow's ‘impossibility’ theorem entails that judgements reached by aggregating grades do not reliably track any collective sense of better and worse at all. These claims are made by adapting the Arrow–Sen framework for social choice to study grading in groups.