One important finding was that having cardinal utilities is not by itself enough to avoid an impossibility result. In addition, utilities have to be interpersonally comparable. Intuitively speaking, to put information about preference strengths to good use it has to be possible to compare the strengths of different individuals’ preferences. See Sen (1970: Theorem 8*2). Interpersonal comparability opens up many possibilities for aggregating utilities and preferences. Two important ones can be read off from classical utilitarianism and Rawls’s difference principle. For details, see the entry on social choice theory.