半總統制和議會內閣制、總統制等，為當今憲政體制研究上之焦點。半總統制之次類型，依據1992年Shugart和Carey提出之分類標準，可以區分為「總理總統制」與「總統議會制」二種類型。在半總統制的適用上，部分國家如葡萄牙、斯里蘭卡等國原先採用總統議會制之次類型，而後透過修憲的方式轉型為總理總統制之次類型。 本文以葡萄牙作為半總統制個案研究之國家，以新制度主義之歷史制度主義為主要研究途徑，並且以文獻分析法和個案研究法之研究方法，探討該國在1974年之康乃馨革命推翻威權政權開始，於1976年制憲進入半總統制之總統議會制類型，1982年時修憲後轉型為半總統制之總理總統制類型，至2000年為止之制度演變情形。研究核心在於該國採用半總統制之背景、次類型轉換之關鍵性因素、採用不同次類型之優缺點與對政治穩定之影響等，本文之結論為葡萄牙在採用總理總統制之次類型後，政治穩定上顯著較前一時期採用總統議會制之次類型高，在制度上亦較為能夠保持長期之均衡狀態。;Semi-presidentialism is a focus of research on constitutional studies. According to the classification standard proposed by Shugart and Carey in 1992, semi-presidentialism can be divided into premier-presidential system and president-parliamentary system. In the adoption of semi-presidentialism, some countries such as Portugal, Sri Lanka and other countries originally adopted the sub-type of the president-parliamentary system, and then transformed into the sub-type of the premier-presidential system through constitutional amendments. This paper choose Portugal as a study case, with the historical institutionalism of the new institutionalism as the main research method, and the research methods of the literature analysis method and the case study method,is aim to discuss from Carnation Revolution in 1974, and entered into a semi- presidentialism with new constitution in 1976 of president-parliamentary system, then transferred into semi-presidentialism premier-presidential system in 1982, and the evolution of the system until 2000. The core of the research lies in the background of the country′s adoption of the semi-presidentialism, the key factors of sub-type conversion, the advantages and disadvantages of using different sub-types, and the impact on political stability, etc. The conclusion of this paper is that after adopting the sub-type of the premier-presidential system, the political stability of Portugal is significantly higher than that of the sub-type of the president-parliamentary system in the previous period, and the system is also more able to maintain a long-term equilibrium status.
