Bubbles are like pornography: Everyone has his or her own opinion as to what qualifies, but it is impossible to pen a precise definition. If you wish to push the metaphor further, both are also fun for a while, if you like that sort of thing, but apt to end up making you feel deflated and embarrassed.

Bubbles are also embarrassing for the economics profession. It’s not that we have no idea what causes bubbles to form, it’s that we have too many ideas for comfort.

Some explanations are psychological. Some point out that many bubbles have been stoked not by markets but by governments. There is even a school of thought that some famous bubbles weren’t bubbles at all.

The psychological explanation is the easiest to explain: People get carried away. They hear stories of their neighbors getting rich and they want a piece of the action. They figure, somehow, that the price of stocks (1929) or dot-com start-ups (1999) or real estate (2006) can only go up.

Read More »