POLS2010 Chap.6 Political Parties and Party Systems
Political Parties and Party Systems
Week 6 asks what parties are and how to describe the systems they form. The chapter compares ideological and instrumental definitions from Burke, Downs and Key, uses Key’s tripod of party in the electorate, party organisation and party in government to diagnose party decline, and contrasts policy-based with clientelistic accountability.
It then moves to party systems: how Lijphart links two-party and multiparty systems to majoritarian and consensus democracy, why Sartori’s counting rules fall short, how Blondel classifies systems by number and size, and how the effective number of parties turns seat shares into a single comparable index.
The week ends with a practical skill as much as a theory: computing and interpreting the effective number of parties.
Because the index uses seat shares, it connects directly to electoral systems in Chapter 8, where the question is whether the rules produce the number of parties or the parties choose the rules.
What this chapter covers
- 01
Ideological and instrumental definitions of a party
- 02
Key’s tripod of three linked groups
- 03
Party decline and falling membership
- 04
Policy versus clientelistic exchange
- 05
Sartori’s coalition and blackmail potential
- 06
Blondel’s four party-system types
- 07
Calculating the effective number of parties
Worked example · free
Diagnosing a party with Key’s tripod
- 1Falling membership weakens the party organisation leg, the members and officials who run campaigns.
- 1Fewer identifiers weakens the party in the electorate leg.
- 1Leading the government shows the party in government leg is still strong, so the party governs while its base erodes.
Key terms
- Effective number of parties
- An index of fragmentation equal to one divided by the sum of the squared seat shares of all parties.
- Clientelistic exchange
- A direct trade in which voters receive gifts, jobs or other targeted benefits in return for electoral support.
- Blackmail potential
- Sartori’s term for the influence of a large party that others will not govern with but which still shapes competition.
- Coalition potential
- Sartori’s term for a party’s relevance as a possible partner in forming a government.
Political Parties and Party Systems FAQ
How do you calculate the effective number of parties?
Convert each party’s seat share to a proportion, square it, add the squares, and divide one by the total. Two equal parties give 2.0, while a 70 to 30 split gives about 1.7, matching the intuition that the system is moving towards one-party dominance.
What is a two-and-a-half party system?
Blondel’s category for a system with two large parties and a considerably smaller third party that may have coalition potential and plays a significant role, such as the German Liberals or the Irish Labour party.
Why does it matter whether parties compete on policy or on patronage?
Under policy exchange, voters support programmes that affect broad groups, which ties parties to policy outcomes. Under clientelistic exchange, parties hand out targeted benefits and monitor small groups of voters, which weakens accountability for public goods and changes how party systems behave.
What is party decline?
It refers to weakening ties between parties and society: falling membership, eroding partisan identification, more volatile voting and growing distrust of party politics. Scarrow and Webb document these trends in established democracies, even though parties still organise governments and legislatures.
Are two-party systems better than multiparty systems?
Majoritarians argue two-party systems give voters a clear choice and produce stable single-party governments, while consensus scholars value multiparty systems for representing more groups and encouraging coalitions. Lijphart links each to a model of democracy and argues the assumed advantages of two-party systems are largely unsupported.
Exam move
Practise the effective number calculation until it is automatic, using invented seat shares with three, four and five parties, and always finish by naming the Blondel category the result suggests. Keep three definitions of a party to hand, one ideological and two instrumental, and be ready to say which you find most useful and why.
Use the tripod as a diagnostic checklist on any party you know, and link party systems back to majoritarian and consensus democracy from Week 2 and forward to electoral systems in Week 8, where the direction of causation is debated. Test your understanding by inventing a parliament and computing its effective number, then changing one party’s seats and predicting the direction of the change before you calculate it.
Finish by writing a paragraph explaining what the number cannot tell you about coalition possibilities, using Sartori’s blackmail potential as the example.
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