 While Condorcet had investigated a particular voting method (majority voting), Arrow, who won the Nobel Memorial Prize in Economics in 1972, introduced a general approach to the study of preference aggregation, partly inspired by his teacher of logic, Alfred Tarski (1901–1983), from whom he had learnt relation theory as an undergraduate at the City College of New York (Suppes 2005). Arrow considered a class of possible aggregation methods, which he called social welfare functions, and asked which of them satisfy certain axioms or desiderata. He proved that, surprisingly, there exists no method for aggregating the preferences of two or more individuals over three or more alternatives into collective preferences, where this method satisfies five seemingly plausible axioms, discussed below.