This thesis investigates why surplus majority government forms. The study focuses on two political systems, Finland and Italy, where oversized cabinets have been the most frequent type of government during the post-war period. The explanatory scope of two groups of theories is tested on two cases of surplus majority government, i.e., the Italian pentapartito-government (1981-1991) and the Finnish rainbow-cabinet (1995). The theories can be considered as two perspectives through which the study of surplus majority government can be approached. According to the theories in the first group the surplus size is a prerequisite for governmental capability. Surplus parties are included because they are necessary for the control of a sufficient legislative majority or for coping with threatening situations.

In the second group of theories oversized governments are possible because theexpected utility of shared government is higher than that of opposition for the political parties. The size, it follows, is not instrumental for governmental capability, but is related to the goal-realisation of the individual political parties, in particular, of the government formateur parties. The picture that emerges in the study is that surplus majority government in Finland and Italy has been the result of both necessitating andpossibilising factors. Requirements of qualified legislative majorities andundisciplined parties have motivated the government formateur parties to include surplus members in the cabinet. However, the main finding is that factors related to the goal realisation of the political parties are more important. The government formateur parties have been better able to control the governmental decision-making to their own advantage by the inclusion of surplus parties. Moreover, the formateur parties have perceived that vote seeking and future attainment of government was enhanced by the inclusion of surplus parties in the government. A shared characteristic of Finland and Italy is the existence of a number of small parties. These parties have preferred government to opposition because their actual opposition influence has been low and the incumbency effect on their votes has been positive or low. Furthermore, the political parties have invented various strategies in order to circumscribe the costs of sharing government.