In 1936, Keynes had frequently contrasted his new theory with what he
called classical economics, much to the benefit of the former, it should go
without saying. The essential difference between the two systems, he insisted,
was that, in his new theory, shifts in the level of investment created shifts in
income and employment, so that prolonged depressions could be attributed to a
chronic lack of investment opportunities. In what he presented as prevailing
classical orthodoxy, on the other hand, such shifts would create variations in the
rate of interest sufficient to ensure that investment would always stay at a level
high enough to fill the gap between income and consumption - ie. saving - at full