| Major powers can exert influence on international institutions via both formal and informal governance.Formal rules are the result of compromise between major powers and small powers,giving the latter disproportionate power and thus failing to meet major powers’ demands.Informal governance fills that void and grants major powers informal influence beyond formal rules.The prerequisite for informal governance is outside options,in form of exit,unilateral action and reduction of investment.Meanwhile,informal governance is constrained by the availability of other states’ outside options and the inadequate governance capacity of international institutions.The above two power-constraining factors produce three combinations,that is,weak constraint,moderate constraint and strong constraint.Three levels of constraints and the availability of major powers’ outside options together produce six informal governance conditions: most unfavorable,very unfavorable,slightly unfavorable,relatively unfavorable,slightly favorable and very favorable,shaping the feasibility and prospect of informal governance.By examining three cases which are United States in the International Energy Agency,Japan in the Asian Development Bank and China in the Asian Infrastructure Investment Bank,the article discusses six conditions and sheds light on the behavior and logic of major powers in various conditions. |