法國與臺灣的政府體制都屬於半總統制，法國的憲政經驗中曾出現過三次的「左右共治」，臺灣的憲政經驗中卻從未出現過「藍綠共治」，何以如此?這是本文欲探討的課題。本文藉助賽局理論作為分析工具，探討制度安排如何影響行動者間的策略互動，以致最後產生了共治與否的差異。法國與臺灣擁有不同的選舉制度和不同的國會保障機制，在兩種制度因素的交互作用下，會引導分屬不同政黨陣營的總統和國會多數產生不同的政治計算與策略互動，最終導致法國出現「左右共治」，臺灣卻沒有出現「藍綠共治」。

Both France and Taiwan’s political systems are semi-presidential. However, “cohabitation” in French constitutional experience has occurred three times while Taiwan has never seen “cohabitation” until now. Finding the reason for this difference is the central question of this paper. By using the game theory as an analysis tool, the paper explores how the institutional design influences the actors’ strategic interactions, which underlies the discrepancy between France and Taiwan in “cohabitation”. France and Taiwan have different electoral systems and different safeguard clauses of the congressional term. Therefore, differences in political calculations and strategic interactions are the two institutional factors that result in the president and the parliamentary majority belonging to different party coalitions, and which lead to the fact that France has seen “cohabitation” while Taiwan has not.