According to the views summarized in Chapter 1, parliamentary regimes are supposed to foster cooperation whereas presidential ones are not. In the former, political parties have an incentive to cooperate with one another; parties in government will support the executive, and parties out of the government will refrain from escalating conflicts owing to the possibility that they may, at any time, become part of the government. Individual members of parliament will also align themselves with their parties. As a consequence, parliamentary governments will be supported by a majority in the legislature, composed of highly disciplined parties that are inclined to cooperate with one another. Presidentialism, in turn, is characterized by the absence of such incentives. Because coalitions are unlikely to emerge, it will frequently generate minority governments. In the rare occasions in which coalitions do form, they will be based on parties that are themselves incapable of inducing cooperation from their members. Thus, coalitions in presidential democracies are rare and are unreliable when they emerge.

We have already examined the incentives for coalition formation under parliamentary and presidential regimes. We saw in Chapter 3 that, once we assume that politicians in both regimes care about being in office and passing policies they like, the incentives for cooperation across regimes are not that much different. In spite of important institutional differences between parliamentary and presidential democracies, the conditions under which governments will be supported by a legislative coalition are almost the same in the two regimes.