The corollary is that even "wasted" votes (eg. for no-hoper third party candidates) matter. Mainstream politicians take those into account and adjust their policies accordingly. They do this because those votes for third parties dilute their own voting base, and they want to avoid splitting off even fractions of their own constituency.

Examples from the UK:

- The Conservatives are desperate to take on policies from UKIP and even the BNP, even though those two parties have no chance of gaining real power.

- The Green party has 1 MP and next to no chance everywhere else, but they have (or had, until the recession) a huge influence on politics.

> - The Conservatives are desperate to take on policies from UKIP and even the BNP, even though those two parties have no chance of gaining real power.

Just out of interest which policies are you talking about?

Limits on immigration. Extreme antipathy towards Europe (eg. the recent budget argument). More in this article: http://www.bbc.co.uk/news/uk-politics-19661190

The US has no third party that is anywhere near as viable as even UKIP or the BNP.

That may change, if the two parties continue to do nothing but spit at each other.