Advantages of a two party political system include stability, simplicity and the ability of the ruling party to govern from a majority position. Disadvantages include the lack of dissenting opinions, the apathy of voters due to lack of alternatives and the inability of third parties to gain traction in government.
In a two party system, each party needs to appeal to a wide base of supporters. Politicians shape their platforms to accommodate the views and desires of a significant portion of voters. One political party is able to obtain a real majority in elections, which promotes stability and decisiveness in government. The system avoids the bickering that often accompanies a multi-party structure, in which efforts to please disparate factions in coalitions lead to stalemates and indecisiveness in leadership.
However, for the sake of inter-party unity, two party systems tend to ignore alternative and radical voices. Multi-party systems, on the other hand, encourage debate and diverse viewpoints, as stronger and weaker parties often have to form coalitions together to achieve political dominance. In two party systems, third parties are stifled because of the winner-take-all voting mechanism in which losing candidates, even if they have significant followings, immediately disappear from relevance. Multi-party systems enable third party candidates to more easily maintain a voice in government.