each voter i, let the ranking of x and y be the same for and for ' . (Different voters could still have different rankings of the 2 social states.) Then the social orderings for the 2 respective sets of orderings select the same state(s) from the subset as the social choice. Arrow describes this condition as an extension of ordinalism with its emphasis on prospectively observable behavior (for the subset in question). He ascribes practical advantage to the condition from "every known electoral system" satisfying it (p. 110). 3. The (weak) Pareto Principle P: For any x and y in the set of social states, if all prefer x over y, then x is socially selected over y.# The conditions, particularly the second and third, may seem minimal, but jointly they are harsh, as may be represented in either of two ways. Arrow's Theorem [1]: The 3 conditions of the constitution imply a dictator who prevails as to the social choice whatever that individual's preference and those of all else. An alternate statement of the theorem adds the following condition to the above: 4. Nondictatorship D: No voter in the society is a dictator. That is, there is no voter i in the society such that for every set of orderings in the domain of the constitution and every pair of distinct social states x and y, if voter i strictly prefers x over y, x is socially selected over y. Arrow's Theorem [2]: The constitution is impossible, that is, the 4 conditions of a constitution imply a contradiction. # Pareto is stronger than necessary in the proof of the theorem that follows above. But it is invoked in Arrow (1963, ch. VIII) for a simpler proof than in Arrow (1951). In the latter, Arrow uses 2 other conditions, that with (2) above imply Pareto (1963, p. 97; 1987, p. 127): 3a. Monotonicity M (Positive Association of Individual and Social Values), as in Arrow (1987, p. 125): For a given set of orderings with social ordering R, such that state x is socially preferred to state y, if the preference for x rises in some individual ordering(s) and falls in none, x is also socially preferred to y in the social ordering for the new set of orderings. Arrow (1951, p. 26) describes social welfare here as at least not negatively related to individual preferences. 3b. As defined by