"Iowa had a Depression too but I don't know if the money supply in Iowa fell during that period. But I guess I'd have to have better reasons man that for giving up on the monetary explanation. The timing and the magnitudes are just right, totally convincing, if you go back and read the Friedman and Schwartz chapter on the Great Depression. But how did it work? We should be able to write down an economic model that kind of explains the workings. How did it happen that bank failures and monetary declines translated into huge movements in employment and production? We just don't have a decent theoretical model. Maybe Rapping and I thought we had, but I don't think we did and I don't think anyone else does now either. I think that has been the problem right along. Is there some other explanation for the 1930s? I don't know. I told Prescott I’d hate to have to rewrite the Friedman and Schwartz book where the role Friedman and Schwartz assigned to monetary collapses is assigned instead to productivity shocks. Where is the productivity shock that cuts output in half in that period? Is it a flood or a hurricane? If it really happened, shouldn’t we be able to see it in the data?"