Good insight from Krugman.

Things That Aren't Bubbles

Is fiat money a bubble in this sense? Not at all. It’s true that green pieces of paper have no intrinsic value (except that they can be used to pay taxes, which is actually important), so that my willingness to accept green paper from you is based only on my belief that I can in turn hand that green paper over to someone else. But there’s nothing to prevent that process of monetary circulation from going on forever. 

So what is fiat money? It is, as Paul Samuelson put it in his original overlapping-generations model (pdf), a “social contrivance”. It’s a convention, which works as long as the future is like the past. Obviously, such conventions can break down — but then so can things like property rights. In fact, you could argue that almost every asset in a modern economy owes its value to social convention; green pieces of paper could become worthless, but then so could any paper claim, which is, after all, worth something only because laws say it is — and laws can be repealed. 

And once you realize that a social convention is not at all the same thing as a bubble, several related fallacies fall into place. 

Take the common claim on the right that Social Security is a Ponzi scheme because the system has few real assets. It’s true that Social Security is mainly a system in which each generation pays for the previous generation’s retirement, in the expectation that it will receive the same treatment from the next generation. But like monetary circulation, this process can go on forever; there’s nothing unsustainable about it (yes, demography, but that’s about the levels of taxes and benefits, not the fundamental nature of the scheme). So there’s nothing Ponziesque at all. 

A final thought: the notion that there must be a “fundamental” source for money’s value, although it’s a right-wing trope, bears a strong family resemblance to the Marxist labor theory of value. In each case what people are missing is that value is an emergent property, not an essence: money, and actually everything, has a market value based on the role it plays in our economy — full stop.

Conservatives assert that social contrivances are "bubbles," things like fiat money, property rights, and Social Security. Is this a category mistake?

Bubbles are "unsustainable."