How do we know if we're in a bubble?

I just read a paper by famous Economist Hyman Minsky, (1919-1996) in which he investigates the recurring instability in markets and developed the idea that there are seven stages in any economic bubble, (even the Dotcom). They are:

1: Disturbance,

2: Expansion / Prices start to go up,

3: Euphoria/ Easy Credit,

4: Over-trading / Prices Reach a Peak,

5: Market Reversal / Insider Profit Taking,

6: Financial Crisis,

7: Revulsion / Lender of Last Resort.

See his paper - Financial Instability Hypothesis [PDF]