Von Kries and the Other "German Logicians": Non-numerical probabilities before Keynes Economics and Philosophy, 17 (2) 2001: 245-273.
Abstract
This essay shows that many of Keynes's most noted ideas on uncertainty, such as the existence of non-numerical probabilities, must be dated back to Johannes von Kries, 1886. Although Keynes explicitly refers to von Kries and other "German logicians" as a source of inspiration for his "weights of the arguments", this connection remained unexplored hitherto.
Apart from filling an evident gap, this historical reconstruction supports an innovative view of Keynes's ideas on uncertainty. It appears, in fact, that non-probabilistic uncertainty is basically cognitive in nature, and essentially due to the imperfection of the analogies drawn by the human mind.