 The former issue is still debated. Extending the informational basis by introducing numerical indices of well-being (or equivalent extended orderings) is not the only conceivable extension. Arrow’s impossibility is obtained with the condition of Independence of Irrelevant Alternatives, which may be logically analyzed, when the theorem is reformulated with utility functions as primitive data, as the combination of Independence of Irrelevant Utilities (defined above) with a condition of ordinal non-comparability, saying that the ranking of two alternatives must depend only on individuals’ ordinal non-comparable preferences. Arrow’s impossibility may be avoided by relaxing the ordinal non-comparability condition, and this is the above-described extension of the informational basis by relying on utility functions. But Arrow’s impossibility may also be avoided by relaxing Independence of Irrelevant Utilities only. In particular, it makes sense to rank alternatives on the basis of how these alternatives are considered by individuals in comparison to other alternatives. For instance, when considering to make a transfer of consumption goods from Jones to Smith, it is not enough to know that Jones is against it and Smith is in favor of it (this is the only information usable under Arrow’s condition). It is also relevant to know if both consider that Jones has a better bundle, or not, which involves considering other alternatives in which bundles are permuted, for instance. In this vein, Hansson (1973) and Pazner (1979) have proposed to weaken Arrow’s axiom so as to make the ranking of two alternatives depend on the indifference curves of individuals at these two alternatives. In particular, Pazner relates this approach to Samuelson’s (Samuelson 1977) and concludes that the Bergson-Samuelson social welfare function can indeed be constructed consistently in this way. Interpersonal comparisons may be sensibly made on the sole basis of indifference curves and therefore on the sole basis of ordinal non-comparable preferences. This requires broadening the concept of interpersonal comparisons in order to cover all kinds of comparisons, not just utility comparisons (see Fleurbaey and Hammond 2004).