Abstract

Collective rationality has attracted much attention by formal theorists, but philosophically, much of it is still poorly understood. The difficulties are easily motivated. As long as we only aggregate preferences (as we do in the case of majoritarian decision-making), there are different proposals for how to do so, and arguments on their behalves can be developed. However, there are voting methods that use rankings other than ordinal ones, and arguments for specific preference-based methods fail to be effective against such methods. For example, no such argument can address a proposal that, say, a committee should make a hiring decision by using a 100-point system. On this proposal, each committee member assigns between 0 and 100 points to each applicant, and then these assignments are aggregated by, for example, averaging. Would that system be as reasonable as purely preference-based methods? Or can we distinguish conditions under which ordinal rankings are appropriate from conditions under which other rankings are appropriate? Such questions call for a theory of voting methods that assesses, first, the conditions under which particular kinds of rankings are appropriate (e.g., ordinal or point systems); second, what specific voting method(s) is (are) appropriate for the specific kinds of rankings; and third, what the criteria for appropriateness are in both cases. Recall that I explained at the start that my most of my research could be understood as interrogating notions of justice and fairness: it is through this search for criteria of appropriateness that considerations of fairness enter here. We are far from having such a theory, and it is precisely this point that keeps me fascinated with this area.