the idea goes back to alvin hansen, who spoke about it in his 1938 presidential address. the american economic association. hansen, of course, was speaking at the latter part of the depression. there in fact, had been a second recession in 1937-38 and unemployment was still about 70%, as best we can tell. and hansen at that time expressed pessimism about the ability of the economy to sustain full employment in the future. he pointed out that demographics were moving in an adverse way at that time. slower population growth. he was concerned about productivity and technology changes and he said super spending would be chronically weak in a way that would prevent the the economy from achieving full employment going forward. now of course hansen didn't quite take that one because after world war ii of course, we had a period of substantial growth, and high employment, relating both to a population boom a baby boom, and also to the application of many technological advances obviously in the '50s an '60s. but larry summers has revived the argument and modernized it, and i just