Arrow's impossibility theorem, Arrow's theorem, or Arrow's paradox is a statement from social choice theory, named after economist Kenneth Arrow, who first described it in 1950: Suppose there is a vote, and voters have at least three different options to choose from. Each voter will then rank the options according to his or her preference. Arrow said, that in such a case, there is no way to convert these rankings into a community-wide complete and transitive ranking while also meeting certain criteria.