7. Arrow's theorem and voting rules

Arrow's theorem effectively established the discipline of social choice. Its significance is suggested by first considering May's theorem on majority rule with two alternatives. We add consideration of the two Arrow conditions of Independence and Transitivity, which become relevant only with more than two alternatives. We then weaken May's conditions of Anonymity, Neutrality, and Positive Responsiveness to Arrow's conditions of Non-Dictatorship, Non-Imposition, and Non-Negative Responsiveness. The practical implication of Arrow's theorem for voting rules is that no voting rule is immune to strategic voting or spoiler effects. Other troublesome or paradoxical features of voting rules cannot be attributed to Arrow's theorem.