[Volpe]

It's a two party system, but the two parties don't have to be the same ones that are their now.

I don't understand the "viable alternative" arguement. You are saying "I won't vote for who I really want to vote, because they'll never win, because everyone else won't vote for them" <--- Is that what you mean? That seems self defeating.

...

[vacri]

If you had rapid iteration - elections every month - then a tertiary party would have something of a chance. As it stands, the iterations are so slow, that with FPTP voting, the two main parties will just move slightly to diminish the threat - the incumbent edifice carries on.

With preferential voting (or similar), you actually have the realistic probability of more than one party being in power. Here in Australia, the current government is formed from one major party, one minor party, and a couple of independents. It's not just 'mathematically possible', but a plausible outcome. That can't really happen with FPTP voting. Well, it can happen, but it's an oddity - see the current situation in the UK with the lib dems.

"I won't vote for who I really want to vote, because they'll never win, because everyone else won't vote for them"

The problem here is that by voting for someone whom you slightly prefer, you split the vote in a FPTP system, making them both lose out to the third person you didn't want in. If 60% of the population want a left-wing candidate, and they're split evenly-ish, they'll still lose out to the single right-wing candidate who only has 40%. It sounds self-defeating on paper, but in real terms it's more like self-preservation.