Alan Siaroff, "Two-and-a-Half-Party Systems and the Comparative Role of the 'Half'," Party Politics, 9 (May 2003), 267-290.

First Paragraph:
In contemporary United Kingdom elections, categoric distinctions are made among the three national parties (the Conservatives, Labour and Liberal Democrats), the two Celtic nationalist parties and marginal parties, with the latter two sets of parties often grouped together simply as 'others'. Yet no one claims that the three national parties are equal, in particular that the Liberal Democrats have an equal chance of (ever) forming a government. Liberal Democratic leaders may be national figures but they are not seen, or scrutinized, as potential prime ministers the way Conservative and Labour leaders are.

Figures and Tables:
Table 1: National party system features, 1945--30 June 2002.
Table 2: Presence of two-and-a-half party systems since 1945 (annual calculations through 30 June 2002)
Table 3: Population and Electoral System Features
Table 4: Population and electoral differences between party systems (t-tests)

Last Paragraph:
[These are the last two paragraphs.]

Two-and-a-half-party systems stand as a distinct sub-type of party system, different from both two-party and multiparty systems. Initially rare in the 1940s, their total number peaked in the late 1970s, but they still remain significant today. Moreover, there has been a geographic evolution in their presence. Through the early 1970s the two-and-a-half-party system was a Germanic (including Austrian) and 'British legacy' (Australia, Canada, Ireland) phenomenon. Through the rest of the 1970s other nations developed such a system, although with the exception of Spain this involved 'onand-off' patterns. By the 1980s we could say that the phenomenon was not strictly speaking restricted to any one or two locations, but nevertheless the core examples seemed to be the Germanic countries, the British Isles and Australia. However~ the late 1980s and early 1990s saw two-and-a-halfpartyism cease to exist in Ireland and Austria, and weaken considerably in Germany. During this same time frame the phenomenon finally acquired permanence in both Portugal and Greece. Thus from the 1990s, and still today, it has been more of an Australian and southern European reality, the United Kingdom notwithstanding. Spain (which has had such a system since democratization) has thus perhaps become the best real world example, consequently really replacing Germany in this regard.

Spain also has (as had Germany before it) the more 'effective' version of the two-and-a-half-party system, that is, where the 'half' party (or group of parties in Spain) is in a hinge position rather than a wing position. This we have seen can make a fundamental difference in the influence of a half-party. Of course, the main overall constraint on the influence of a half-party remains the achievement of a single-party majority by one of the two main parties -- a standard outcome in the United Kingdom and largely the case in Greece, but in contrast an occasional (Spain), rare (Portugal) or non-existent elsewhere.