I don’t often discuss macroeconomics here but this blog post by John Quiggin is well worth my attention and yours. He totally demolishes a review of his book by Steven Williamson, who is quoted as saying “Market efficiency is simply an assumption of rationality. As such it has no implications. If it has no implications, it can’t be wrong.” Williamson is also quoted as saying “Like the “efficient markets hypothesis,” DSGE has no implications, and therefore can’t be wrong.”
If you wonder why I have not gone over to my university’s online library site to read the review, it’s because I am utterly disgusted by the Williamson quotations and do not want to waste my time reading his review. Macroeconomics is supposed to be a science, not a part of analytic philosophy or logic; “economists” with such enormous blindfolds as Williamson have too much sway in the discipline and have corrupted its very core.
Like Tjalling Koopmans said in response to Milton Friedman’s methodological emanations, every assumption you make in building a theory is automatically, and rather obviously, also a prediction of the theory. Saying “I like the assumption of rationality, I will always make it, and it’s my mode so you can’t tell me not to play with it to my heart’s content” is odious nonsense. When the efficient market hypothesis or DSGE is part of a model that produces predictions that keep being smacked by the data, insisting that these assumptions (and since when is DSGE an assumption, rather than a whole modeling technique?) can’t be wrong is tantamount to saying that your theory can’t be useful and in fact is eminently ignorable. If you peddle it to the world and your students as science, you are at the minimum corrupting the notion of science itself.