On fiat money and little green pieces of paper

Things That Aren’t Bubbles

Paul Krugman, NYT

Noah Smith, who is a better human being than I am, wades through an anti-Krugman rant to find an interesting nugget: the claim that money is a bubble. It isn’t, of course; but my explanation of why it isn’t is a bit different from his, and has wider implications.

I’d start by asking, what do we mean when we talk about bubbles? Basically, I’d argue, we mean that people are basing their decisions on beliefs about the future that are based on recent experience but can’t be fulfilled. E.g., people buy houses because they expect home prices to keep rising at a pace that would eventually leave nobody able to buy a first home.

Bubbles don’t have to involve prices. You can have a local construction boom driven by rapid growth in an area’s population and employment, when the main thing driving that rapid growth is … the local construction boom, which will eventually collapse when enough houses are completed. The point, whether prices are involved or not, is that the expectations of individuals add up to an aggregate impossibility.

(More here.)