Applying growth theory across countries

I am broadly in sympathy with the spirit of the article by William Brock and Steven Durlauf and that by William Easterly and Ross Levine. They are trying to move the literature in the right direction. I say this even though I have been skeptical from the beginning about the interpretation of cross-country growth regressions. The potential problem of reverse causality has been obvious to everyone. It has usually been met with the standard econometric dodge: using lagged values of slow-moving variables as instruments. But this cannot be a serious solution to the problem. The causality issue points to a deeper question: Do cross-country regressions define a meaningful surface along which countries can move back and forth at will? If this is the idea, what mechanism could underlie such a sur-face? Brock and Durlauf call such a regression a “model. ” I suppose in a statis-tical sense it is. But an economic model should have some internal structure; its causal arrows should rest on some sort of behavioral mechanism, and that seems to be missing in this literature. I think I had this prejudice even before cross-country regressions became fash