Giovanni Sartori, the Italian political scientist, was reacting against sociological explanations of parties and wanted to treat parties as independent institutions from a more clearly political science point of view.

Sartori was also unhappy with Duverger’s division of party systems into either two party or multi-party and developed a more detailed classification of parties based on three criteria:

The number of significant parties. Significance is defined by whether a party is a potential coalition partner or whether a party has blackmail potential because its appeal can attract voters away from another party.

If the parties are ranked along a left-right continuum, the distance between the most left wing and the most right wing party i.e between the two poles of the party system.

The interaction between the poles i.e. whether parties are converging towards the centre or diverging towards more extreme positions.

Based on these criteria, Sartori defined a number of party system types of which the most important were moderate pluralist and polarized pluralist.

He held that two party systems and limited pluralist systems with low ideological distances would be centripetal and converge towards the centre, while more polarised systems with 3-5 parties would suffer instability and opposition to the governing parties from anti-system parties to the left and right (the post-war party system in Italy until the dramatic changes in the 1990s fits this pattern and no doubt influenced Sartori’s views).

Paul Pennings criticised Sartori based on a study of party systems in the 1980s and 1990s which shows that it was the more polarized systems that were converging to the centre in policy positions (‘The Triad of the Party System ’ in P. Pennings and J-E Lane (eds.) Comparing Party System Change, 1998 and see the reply by Jocelyn Evans in Party Politics Vol 8 No 2, 2002).)(Also see Tom Quinn Political Studies Vol 62 No 2, 2013 for a recent use of Sartori’s theory in looking at the British party system).

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