"[Classical economists] were still dealing with a system in which the amount of the factors employed was given and the other relevant facts were known more or less for certain. […] The calculus of probability, tho mention of it was kept in the background, was supposed to be capable of reducing uncertainty to the same calculable status as that of certainty itself […] By "uncertain" knowledge, let me explain, I do not mean merely to distinguish what is known for certain from what is only probable.