What is the best system? The multi party or the two party system?

What are the advantages of a two-party political establishment over a multi-party system?

• The United States comes to mind, but insight on other examples are welcome.

• Answer:

  I'm about to show you an example of tyranny and oppression.  But I'm going to warn you it's quite graphic and you may not want to look. A small group having its way with the majority and running the government in direct opposition to their values as expressed in the ballot box.   The right of the people flaunted, the obvious election loser given the crown... Yes, it's the Canadian Federal Election of 2011. OK.  maybe it's not that graphic.  IN fact it even looks like the people with the largest bar won and all is right with the world.   But the reality is, Canada got hosed and a political philosophy that wasn't wanted won the day. As you can see, Canada clearly wanted a Left government and got a Conservative one.  The vote was 53% for three left-leaning parties, Liberal and New Democratic party and Greens.   But the party with less than 40% won. (I'll put aside the 6% for the separatist Bloc Quebecois for the moment) So a two party system, much derided can avoid this kind of tyranny of Plurality.     Multiparty systems are sometimes seen as a good thing, especially as a decent group of Americans are tired of both major US parties and crave change.  But at least with 2 parties, well you generally  get a President that the majority of people voted for (now we had that 2000, 1888, 1876 and 1824 election, but you know, most of the time pop votes wins.) Theres also the Tyranny of Exaggerated Influence when elections are deadlocked and several parties have influence well beyond their minimal endorsement by the electorate.     Tyranny and Dopplegangers The 2010 UK election demonstrates the trouble of.  The country voted 306 seats for Conservatives, 258 for Labour.  57 for Liberal Democrats.  Straight up democracy, absent the horse-trading and coalition building, woudl say that the Liberal Democratic Party has no place in anything.  The 57 for 'Yellow' was a loss of 5 seats for them.  Yet because the other two parties could not claim majority (Blue came close but not enough.)  The Liberal Democratic party, on a downward trend, became coalition partner with the Conservatives.  Do they deserve it?  They didn't come in second after all.  Conservatives almost won and yet this party with little support is getting the Deputy prime minister spot and a couple of ministries and influencing government (slowing down too much for some Conservatives)   But few care now becauase the tyranny argument hasn't totally proved in practice.   It's not too much influence, so this factor may not be so apparent in the 2010 UK case.    There are other coalition based countries where the tyranny of ministers of small parties is more apparent.  (Just in case one thinks I might be too hard on the coalition I note that Labour very much wanted the Lib Dems in coalition, and that Gordon brown had considered putting together a coaliton of many little parties to retain power, which would have been more undemocratic than the Plurality Party winning the government. ) Here's the larger problem with the Liberal Democrat that is the one most visible in the UK.  Then there's the problem with coalition government which I might call a 'Doppleganger Effect' Your parties change when they jockey for coalition.  So in the US you have absolutely what values you are voting for in your government.    Not so in a coaltiion.  Liberal Democratic voters got a coalition government that is mostly conservative.  Many of their voters voted for the LibDems with no expectation that they would unite with the party called 'the Tories' by opponents.  As a result Clegg's popularity has suffered.  Esp. after unpopular budget moves and a raise of tuition fees.  I know US politicians can change a bit when they get in office, but I would say it is far more difficult voting in coalition systems to figure out what you will be getting when you vote.    The party's set of values isn't information that helps you anymore, it's something you ahve to make an impossible calculus about - how would these values 'morph' into a coalition?  No thanks.