"In 1972 American economist Kenneth Arrow, jointly with Sir John Hicks, was awarded the Nobel Prize in economics for “pioneering contributions to general equilibrium theory and welfare theory.” Arrow is probably best known for his Ph.D. dissertation (on which his book Social Choice and Individual Values is based), in which he proved his famous “impossibility theorem.” He showed that under certain assumptions about people’s preferences between options, it is always impossible to find a voting rule under which one option emerges as the most preferred."