This review attempts to utilize two main theoretical approaches in comparative politics-affect and rationality-to analyze the plausible unification or separation of the Kuomintang (KMT) and the People First Party (PFP). It categorizes the so-called unification or separation of the two parties into three conditions: first, a clear-cut separation between the two parties, where the two would even become rivals; second, the two parties not only cooperate but also compete, which is similar to the current situation; third, an eventual unification of the two parties. Based upon the historical records of the separate and cooperative relationship that have appeared between the KMT and the PFP, the paper points out that rational choice plays a more crucial role than the affective bond in this process, which means the rational calculation of each party for votes or power under a certain institutional arrangement is the dominant force in making the KMT and the PFP allies or enemies. Thus the paper considers that the future plausible relationship between KMT and PFP should be mainly decided by their rational, not affective, choices.