An Arrowian social welfare function is single-valued. That is, to any set of individual orderings a social welfare function assigns one, and only one, social ordering. While other features of the Arrowian framework have given rise to a huge volume of literature, single-valuedness does not seem to have attracted any attention at all and, on the face of it, this may seem hardly surprising. After all, given that social choice is to depend on a binary relation of social preference (or what has been called a relational procedure in Sen (1977)), single-valuedness seems natural and unobjectionable. Furthermore, it is not clear that anything can be gained by relaxing it. However, the question of single-valuedness and its implications is not quite so simple.