remarks of real cost:
141-142 (pdf 174-175)
All attemts to reduce the complex structure of waiting periods, which is described by the input functions ^and^ the ouptu functions, to a single aggregae or average investment period, which could be generally subsitituted for these functions in the discussion of the productivity of investment, are bound to fail, because the different waiting periods cannot be reduced to a common denominator in purely technical terms. This would only be possibe provided we had to deal with only one homogeneous kind of input, and provided the value of the product were always directly proportional to the amount of this input that was used. Of course neither of these assumptions is true in reality. But it is such ideas as these, dating back to the real cost theories of value, which have until quite recent times disfigured and invalidated much of the theory of capital.
375 (pdf 408)
The reason why Mr. Keynes does not draw this conclusion, and the general explanation of his peculiar attitude towards the problem of the determination of relative prices, is presumably that under the influence of the “real cost” doctrine which to the present day plays such a large role in the Cambridge tradition, he assumes that the prices of all goods except the more durable ones are even in the short run determined by cost. But whatever one may think about usefulness of a cost explanation of relative prices in equilibrium analysis, it should be clear that it is altogether useless in any discussion of problems of the short period.