 Sen (1970a) proposes a further generalization of the social choice framework, by permitting consideration of information about individual utility functions, not only preferences. This enlargement is motivated by the impossibility theorem, but also by the ethical relevance of various kinds of data. Distributional issues obviously require interpersonal comparisons of well-being. For instance, an egalitarian evaluation of allocations needs a determination of who the worst-off are. It is tempting to think of such comparisons in terms of utilities. This has triggered an important body of literature which has greatly clarified the meaning of various kinds of interpersonal utility comparisons (of levels, differences, etc.) and the relation between them and various social criteria (egalitarianism, utilitarianism, etc.). This literature (esp. d’Aspremont and Gevers 1977) has also provided an important formal analysis of the concept of welfarism, showing that it contains two subcomponents. The first one is the Paretian condition that an alternative is equivalent to another when all individuals are indifferent between them. This excludes using non-welfarist information about alternatives, but does not exclude using non-welfarist information about individuals (one individual may be favored because of a physical handicap). The second one is an independence condition formulated in terms of utilities. It may be called Independence of Irrelevant Utilities (Hammond 1987), and says that the social ranking of any pair of alternatives must depend only on utility levels at these two alternatives, so that a change in the profile of utility functions which would leave the utility levels unchanged at the two alternatives should not alter how they are ranked. This excludes using non-welfarist information about individuals, but does not exclude using non-welfarist information about alternatives (one may be preferred because it has more freedom). The combination of the two conditions excludes all non-welfare information. Excellent surveys are given in d’Aspremont (1985), d’Aspremont and Gevers (2002), Bossert and Weymark (2004), Mongin and d’Aspremont (1998). In spite of the important clarification made by this literature, the introduction of utility functions essentially amounts to going back to old welfare economics, after new welfare economics and authors such as Bergson, Samuelson and Arrow failed to provide appealing solutions with data on consumer tastes only.