This document outlines the basic concepts of economic theory that are used to evaluate alternative social states, based on the formulation of a social welfare function that either permits or denies interpersonal comparisons of utility. Specially, it shows different approaches of old and new welfare economics. And concludes that Amartya Sen’s contribution to the concept of welfare as functioning and of justice as capacity to choose among different functionings, makes it possible to consider agents differently and to evaluate alternative options of life conditions.
