Phrases using two or twoness

• We often use two when we have an alternative and a choice to make: we might be in two minds, then select the lesser of two evils, or we could deny a choice by saying there's no two ways about it.
• Someone who cheats could be two-timing us, and we might describe a liar as two-faced. We might issue them a challenge by saying 'two can play at that game'. On the other hand, we might emphasise agreement by saying 'that makes two of us'.
• Two can also be a helpful addition: we may have two bites of the cherry, have two strings to our bow or we may say two heads are better than one.
• Finally, it can be used to emphasise a very small quantity. We might offer our two cents' worth or tuppenceworth, or put two and two together to draw a conclusion from simple facts.

See http://www.bbc.co.uk/dna/h2g2/A45901749