共治乃總統與總理來自不同政黨（或聯盟），且總統所屬政黨（或聯盟）不在內閣組成當中，因此，在府會不一致下，共治將基於「總統；國會多數與內閣組成多數一致」；「總統；國會聯盟；聯合政府」的兩種樣態，體現政黨體系在其中的重要影響。於1990年代加入半總統制陣營的新興民主國家中，政黨體系的相對不穩定，是許多國家共同存在之現象，而在這些新興半總統制國家中，多黨制的政黨體系更是伴隨共治出現，並影響其共治運作的關鍵，基此，本文將選擇10個新興半總統制國家，比較其政黨體系與共治的關連性。首先，本文將藉國會有效政黨數的計算，展現相異政黨體系所形成的共治樣態，將共治再分類；其次，本文將國會的政黨體系延伸至其對政府運作與存續之影響，討論共治期間的政府組成以及內閣存續天數和政黨體系的關係。最後，本文將藉各國政黨體系影響下的共治運作案例，說明政黨體系的樣態及其零碎性是否實質影響憲政運作之穩定。本文認為，在政黨體系的因素外，仍應考量政黨聯盟的緊密性；總理角色；總統憲政權力，以及一國制度是否固著等因素，因此，政黨體系的穩固並非一定帶來半總統制便因共治而轉向內閣制的軌道，同樣地，政黨體系的零碎性也不必然會帶來半總統制國家在共治期間的不穩定性。

By centering on political party systems, this paper aggregates the effective numbers of parties and patterns of majority formation which assays the connectedness of political party coalitions with the executives and the parliaments in newly semi-presidential countries. Theorists often concentrate on the cohabitations of the interactive relations of the executive powers between presidents and prime ministers but less often refer to the relations through which presidents and prime ministers respectively interact with governing coalitions (the executives) and parliamentary coalitions (the legislatures). Hence, on examining the situations in which newly semi-presidential countries frequently form coalition governments under multiparty systems, this thesis promotes that the factors of the party influence of presidents, the executive orientation of prime ministers, or the competition and cooperation of parliamentary coalitions and of the executives, and so on, will complicate the patterns of cohabitation operation. Therefore, this paper investigates the party systems to examine the triangle relations among the presidents, the prime ministers and the parliaments, through which the types of cohabitation can be scrutinized. This thesis gathered materials in ten countries and investigated profoundly and thoroughly these countries' cohabitation experiences. This paper will also make comparisons of political party systems during the cohabitations, and see how the political party systems deepen or convert the implications, and embody the ＂formation＂ and the ＂shift＂ of cohabitations in these newly semi-presidential countries.

半總統制；共治；政黨體系；國會

Party System; Cohabitation; Semi-presidential Countries; Congress