Erik Moberg ã:
A Theory of Democratic Politics
2.1 - DECISIVE AND BLOCKING POWER
In part 2 I made a distinction between decision-making power and procedural power. Here, as a preparation for the subsequent discussion, I will continue by splitting decision-making power into the two concepts of decisive and blocking power.
For illustrating I will assume, as a very simple example, that we have a single decision making group consisting of 100 persons, and that a majority of 3/4 is required for an affirmative decision. If so, any set of 75 persons, or more, can make a proposal pass. Such a set is thus decisive, and it holds decisive power. Conversely any set of 26 persons, or more, can block the passage of a proposal - such a set is consequently blocking and it possesses blocking power. The concepts can also be described by saying that a decisive set is needed for changing the status quo, while a blocking set is enough for hindering a change of the status quo.
These concepts can, of course, also be used in more elaborated situations. Here we are for instance usually considering complexes including both an executive and a legislature, the latter possibly having two houses. In such situations it is always possible to describe exactly which composition a set must have in order to be decisive, and in order to be blocking. We just have to know the decision-rules exactly.
It is often easier to form a blocking set than a decisive one. Such, for instance, was the case in the example above, where a qualified majority was stipulated: 75 persons were required for dictating a decision whereas 26 persons were enough for blocking it. The same is true in a number of situations of interest for the discussion here. It is for instance true if there are two houses in the legislature, and a proposal, in order to pass, must be affirmed in both houses, even if only with a simple majority in each house. If so a majority in either house is enough for blocking a proposal, whereas a majority in each house is required for making it pass. Another example is a presidential system in which the affirmation of both the president and the legislature is required, even if there is only one house, and even if only a simple majority in the house is required. Obviously, in such a case, the president alone, or a majority in the legislature alone, is enough for blocking a proposal, whereas the acceptance of both the president and a majority in the legislature is needed for changing the status quo. There are, however, also situations, in which it is as difficult to form a blocking set as a decisive one. Consider for example a situation in which a simple majority in a one house legislature is enough for passing a proposal. In such a case the same kind of set, that is a simple majority, is obviously also needed for blocking the proposal.
The distinction between decisive and blocking sets is, of course, commonplace in social choice theory. Now and then it also appears in texts primarily devoted to constitutional problems. One example is Shugart & Mainwaring (1997, p 41) who call the power to change the status quo proactive power, and the power to block changes of the status quo reactive power. The concepts of positive and negative power may also be used.