In 1962, political scientist William Riker published The Theory of Political Coalitions. The key idea in this book was that of the minimum winning coalition, for short MWC, which goes like this:
Politicians seek to maximise votes in order to maximise seats in parliament, in order to win the cabinet. The less parties you have to share with, the more seats you get in cabinet. A political coalition is a zero-sum game with (partially) rational actors. Each actor has full information about the weight of other players (coalition building takes place after votes are counted), and parties cannot share a ministerial position. What one actor has, the other loses.
Therefore, parties will seek to form a coalition that is as small as possible, while still winning. That may not be so odd, but Riker went further to say that parties do not give anything for policy, so they will form whatever coalition they like, regardless of policy.
Now, you might say that this is plain silly. Because we know that parties have profiles, and some profiles just do not match. Would a far-right party gladly join a far-left party if the votes add up? Noo. Besides, if voters are expected to be rational, they would be quick to punish parties that do not keep their promises. You might go on to observe that Riker’s theory actually predicts only few cases. For Riker, though, this was not important. What is important was that his theorem gets you thinking about what explains varying constellations of coalitions, including size and durability.
Political scientists have long pondered his theorem, refining and deepening our understanding of the workings of different systems. They note that a coalition must not only be WINNING, it must also be VIABLE, which often means that members of a coalition must be relatively closely positioned, for instance on a ‘left-right’ policy dimension. They note that a,s a rule of thumb, ruling is costly in terms of votes; voters will usually punish the government in the next elections, hence it can be a good idea for a coalition at the outset to be larger than minimum. Further, there are differences between how influential the government is, as opposed to the opposition. For instance, in the Danish system, we had a minority government for several years taking the lead on fiscal and monetary policy while largely following the word of the opposition as regards foreign policy. All these points, and more like them, help to explain why only a small number of actual coalitions resemble the minimum winning coalition in Riker’s understanding.
Every now and then, however, political events present us with what seems at the outset a pure form of Riker’s minimum winning coalition. The most recent I have seen is this Jakarta Post article reporting that in the upcoming presidential elections, a coalition between PDI-P (People’s Democratic Party of Struggle) and PKS (Prosperous Justice Party) fares very well in a poll.
The poll says that Susilo, the incumbent president, is the most popular presidential candidate, but that with his current vice president, Jusuf Kalla, the team would only get 20 per cent. With Yogyakarta sultan Hamengkubuwono X, Susilo should get ten percentage points more, but still be behind the pair of Megawati of PDI-P and Hidayat Nuw Wahid of PKS.
As the Jakarta Post article states:
“Indonesian Science Institute (LIPI) researcher Alfan Alfian said the Puskaptis survey was suggesting an almost unthinkable coalition of the PDI-P and the PKS in the presidential election. “It is interesting because the two parties promote different ideologies,” he said.”
The response, so far, from PDI-P is:
“We will study the survey, including its methodology and respondents… We will open our minds to public aspirations, including opinion surveys. We want to know the public’s response if Megawati pairs with Hidayat, Akbar Tanjung, Sultan or Kalla.