Arrow’s rationale for requiring aggregation procedures to handle many profiles was epistemic. As he framed the question of collective choice, a procedure is sought for deriving a social ordering of some given alternatives on the basis of some given people’s tastes and values. It is sought, though, before it is known just what these tastes and values happen to be. The variety among profiles to be reckoned with is a measure, in Arrow’s account of the matter, of how much is known or assumed about everybody’s preferences a priori, which is to say before these have been elicited. When less is known, there are more profiles from which a social ordering might have to be derived. When more is known, there are fewer of them.