Introduction

Social choice theory has traditionally been dominated by negative results. Starting with Arrow's famous impossibility theorem, authors have formulated seemingly reasonable conditions that a preference aggregation procedure ought to satisfy, and then proved that the conditions are logically inconsistent.

As has been observed by several authors, one reason for this state of affairs is the extremely weak informational basis on which a social choice function is supposed to work: The input to the function consists of ordinal and noncomparable preferences.

In this chapter, I shall investigate the consequences of introducing a certain type of preference comparability, which I shall call subjective comparability. I explain and motivate the concept in this Introduction; details come later. Throughout the chapter, I stick to the standard assumption that preferences are purely ordinal.

Previous authors have incorporated interpersonally comparable preferences into the social choice framework in the following way: The input to the social choice function is an ordering of the pairs (x, i), where x is a social state and i is an individual. This ordering includes information about each individual's ranking of the states, but it also contains answers to questions of the type: “Is it better to be individual i in state x than individual j in state y?” If one now introduces conditions analogous to the standard conditions of social choice theory, many of the negative results – including Arrow's impossibility theorem – do not reemerge.