John Maynard Keynes and Johannes von Kries History of Economic Ideas, 6 (3) 1998: 51-80.
This essay sheds light on the fundamental influences of a German logician on Keynes' ideas on uncertainty, a source referred to explicitly by Keynes as inspiration for his "weights of the arguments". This study suggests that many of Keynes' most noted ideas on uncertainty, such as the existence of non-numerical probabilities as well as the "weights of the arguments", date back to Johannes von Kries, 1886.
Apart from filling an apparent gap in the history of economic thought, the historical reconstruction put forth in this essay supports an innovative view of Keynes' ideas on uncertainty. It appears, in fact, that non-probabilistic uncertainty is basically cognitive in nature, due essentially to the imperfection of the analogies drawn by the human mind in its attempt to frame empirical experience by classifying empirical facts into mental categories.