by ‘uncertain knowledge’, let me explain, I do not mean merely to distinguish what is known from what is merely probable. The sense in which I am using the term is that in which the price of copper and the rate of interest twenty years hence, all the obsolescence of a new invention are uncertain. About these matters there is no scientific basis on which to form any calculable probability whatever. We simply do not know.
However, Keynes’ admonition to open up the field of economic decision-making to the unknown unknownswas entirely neglected in the subsequent development of mainstream economics (including mainstream Keynesian economics).