contexts the main restriction of coalition formation is ideological: if any subset
of actors can form a coalition only on specific, precise and short-term issues,
coalitions will be short-lived, unstable and unpredictable. In international
relations, for example, the traditionalbalance-of-powertheory relies pre-
cisely on the notion that there are no ideological barriers to any coalition
forming. In extreme cases of domestic politics one can find the same ‘open
texture’ to coalition potential. In both domestic and foreign affairs, however,
such openness is unusual, and the range of possible coalitions is much
diminished.Coalition theory, the study of the formation of coalitions, has
been the study of one of the more successful political science theoretical efforts
since the 1950s, and powerful predictive theories, based in part ongame
theory, have been derived and tested.
Coalition Theory
Coalitiontheory, much of which developed fromgame theory, is part of the
quasi-mathematical rational choice tradition in political science which
attempts to construct predictive theories to explain political activity. There
are two principal domains of political activity to which coalition theories have
been applied: the forming of a government by a coalition of minority parties in
a parliament, and the forming of military and diplomatic alliances between
states. However, the advocates of coalition theory would claim that it ought to
apply to any situation where more than two actors face potential conflicts of
interest, and thus co-operation between two or more against one or more
opponents is rationally useful. They would further argue that at least the
general form of a successful theory would apply to any sample, whether it dealt
with a coalition of small firms against a potentially monopolistic rival, a
coalition of parties to form a government or a coalition of schoolchildren
against the playground bully.
In the example of government formation coalition theories have been quite
successful, especially when applied to party systems where the number and
sizes of parties, as well as the ideological spectrum of the nation’s politics, leaves
no obvious coalition grouping. One of the two principal rules to emerge from
early work in this sphere was that the most likely coalition to form will be what
is called a ‘minimum-winning’ coalition. In a parliament where 70 seats are
needed to form a government, and there are four parties (A–D), running from
left to right of an ideological spectrum, A having 50 seats, B 40 seats, C 20 seats
and D 10 seats, it is more likely that a two-party coalition of A and B will form
than a three-party coalition of B, C and D. What will almost certainlynotform
is a coalition of all four, because such a government would have 50 more seats
than it needed and, as a party loses potential benefits the greater the number of
other parties with which it has to share the value of being in government, there
Coalition Theory