In the first chapter, we generalize Asan's weak path independence and Woeginger's reducibility to subsocieties for two alternatives to any set of alternatives. Given a society of finite individuals and any set of alternatives, we discuss the sufficiency and necessity condition or sufficiency condition when the social welfare function is a majority rule; Given a society of finite individuals and finite set of alternatives, we define the majority rule as a social choice rule and give some sufficiency and necessity conditions when the social choice rule is the majority rule in the second chapter. |