Reduction in Economic Theory

The recent financial crisis has provoked a lot of interesting discussions about the state of macroeconomic theory, and one aspect of this that I’ve been interested in is the revelation (to me) that a lot of the macro theory of the past 30–40 years has been driven by a sense that a theory is no good unless it has “micro-foundations.” This is interesting to me largely because while I can’t do hard math like a real economist, this is closely related to things people talk about in philosophy classes. At any rate, John Quiggin, pushing back against the micro-foundation trend, writes:

If we are to develop a macroeconomic theory that can help us to understand, and hopefully prevent the recurrence of, crises like the current one, and help us to improve policy responses, economics must take a different road from that it has followed since the 1970s. The appealing idea that macroeconomics should develop naturally from standard microeconomic foundations must be recognised as a distraction. In its place, we must accept, in the language of systems theory that macroeconomic phenomena are emergent, arising from complex interactions of behaviors we do not fully understand, but must nevertheless respond to.

I think this is the wrong way to generate that conclusion. What I think Quiggin ought to say is that macroeconomic theory needs to distinguish between two different kinds of questions about foundations. One is a somewhat metaphysical issue about whether or not it’s the case that macroeconomic propositions are ultimately reducible to microeconomic phenomena. This is related to issues about whether or not mental processes are ultimately reducible to biological processes in the brain (or does the mental supervenes on the physical without being reducible to it) whether moral facts can be reduced to physical ones (as in Cornell realism) and so forth.

The other — and quite different — issue is a methodological question about whether it really makes sense to demand that macroeconomists produce microfoundations for their theories. We learned a great deal about chemistry before we understood the structure of the atom in detail. When Darwin proposed evolution by natural selection, he couldn’t provide the genetic microfoundations the theory required. And when Mendel pioneered genetics, he couldn’t provide the chemical microfoundations that the discovery of DNA provided later. As it happens, microfoundations have been discovered for most of this stuff. But the theories weren’t initially accepted because they had strong microfoundations, they were accepted because they worked well as theories on their own terms. A macroeconomic theory that’s based in elegant microfoundations but that doesn’t actually explain the economy well is useless. But that doesn’t require you to commit yourself to any strong claims about the ultimate metaphysical status of the discipline.