Take Giovanni Sartori's seminal Parties and Party Systems as an example. In his discussion of what parties should and should not be counted as part of a party system, Sartori rules out those parties unable to secure parliamentary representation. All that really matters are the relative strengths of parties, measured by the number of seats they hold. But even crossing this representation threshold is not enough: party system actors are counted only if they possess enough seats to have ‘coalition’ or ‘blackmail’ potential. Coalition corresponds to parties who have formed a government in the past, participated in a governing coalition, and/or is perceived by other parties as a potential coalition partner. Blackmail potential on the other hand covers all other parties who retain substantial representation while refusing to participate in government (usually on ideological grounds). Lijphart (1999) suggests that while Sartori is useful for determining the significance of parties in a system his classification is blind to the number of parties present within it. An alternative measure proposed by Blondel (1968) looks both at the numbers of parties present in the parliamentary system plus their size. To illustrate, using the present UK Parliament, ten parties currently have representation - but only two are significant in terms of government participation. The Liberal Democrats and their historical antecedents have since the early 1920s only had occasional blackmail potential in exceptional circumstances, such as significant backbench rebellions or during periods of minority government. The same applies for the loyalist parties of Northern Ireland and the SNP.
The problem with this political science approach rests on the conceptualisation of significance. By bringing the analytical focus to bear on small parties the assumptions underlying significance become visible and begin to unravel. What is clear is that significance, regardless of measure, is narrowly conceived in terms of a party’s relationship to office. By extension the privileged field of analysis is parliamentary activity, which is taken to be synonymous with the party system as a whole. In turn this serves to reinforce the hegemonic view that politics in parliamentary democracies is properly the business of vote gathering. The view of politics as something that occurs outside sanctioned elected bodies is simultaneously ignored/suppressed. Parliamentary politics is the unmarked term. It is the assumed norm.
Significance acts as a conceptual gatekeeper. But by diligently performing its duties of defining, measuring, and excluding parties, by upholding and policing the party system concept, it paradoxically undermines its explanatory efficacy. In fact there are a number of ways parties invisible to the significance criteria can have impacts on party systems. Herzog (1987) argues small parties assist in the articulation of new political norms, that such parties are guinea pigs for new ideas. (The oft-cited example in this context is the impact Green parties have had on the mainstream policy agenda, despite their lack of “significance” in terms of the UK Westminster party system). As Carty (1997) observes small parties can “set in motion a set of responses from other parties that [transform a] country’s competitive politics” (p.97). Similarly (though writing about parties who tend to fulfill significance criteria) Capoccia (2002) and Abedi (2004) argue anti-system parties can affect a system’s legitimacy and stability, and its functioning by pushing it in a polarising direction.
For example, despite being micro-parties of no relevance under the significance criteria, both the SWP and SP have had at one time or another an impact on the party system. The SWP played a leading organisational role in the anti-Iraq War movement by helping mobilise a constituency that it later benefited from electorally via Respect. Thanks to its efforts for keeping it a live issue it can be argued that it (inadvertently) assisted the growth of the Liberal Democrat’s parliamentary support (4,814,321 votes and 52 seats at the 2001 election to 2005’s 5,981,874 votes and 62 seats). Similarly in its Militant heyday the SP had three MPs sitting as Labour members, and its role as the organisational backbone of the Anti-Poll Tax Federation was a significant contributing factor to the resignation of Margaret Thatcher and the declining electoral fortunes of the Conservatives in the 1990s.
What this suggests is the necessity for a conceptual reworking of both significance and party system to put them on a sociological footing, so the impacts of very small parties and/or social movements can be properly theorised.