半總統制最大的特徵是行政權的二元化，但就憲法設計的本質上，有兩種雙元行政的差異，這兩種雙元行政影響了半總統制在常態下的運作軌道，也影響半總統制偏向議會內閣制或是總統制轉型的可能。第一種本研究定義為垂直式的雙元行政，是一種分時治理的概念。常態下由代表政黨的總理領導的政府扮演最主要的行政權，因此向國會負責為必要條件。當陷入危機狀態才由代表人民而非代表政黨的總統領導。第二種本研究定義為水平式的雙元行政，一種分權治理的概念。不分常態與非常態，總統和總理各自擁有一部份的行政權，藉由政黨政治表現出權力融合或競爭的樣態。在分時式的雙元行政下，只要政黨體系穩定，容易建立議會化的半總統制。在分權式的雙元行政，在不同政黨掌握總統與國會多數時容易出現共治、少數政府；而相同政黨掌握時，則傾向總統領導。 Semi-presidentialism is a constitutional system with dual executive. According to the essence of constitution, there might be two different kinds of dual executive systems. One of them is called as a vertical dual executive system and the other is a horizontal dual executive system. Under the vertical dual executive system, the prime minister is the leader of the government base on a parliamentary majority. The president will player a political leader only in emergency. Under the horizontal dual executive system, the president and the prime minister are both political leaders. The cohabitation or the minority government will occur when the president is the minority in the parliament. However, the president will be also a stronger leader when he controls the parliamentary majority.
