# On Keynes’s November 9th,1936 Decision to Qualify His December 12,1935 Acknowledgement to J. Robinson of Her Help Contained in the Preface to the General Theory in Correspondence: Robinson’s Extraordinary Mathematical Illiteracy Meant that It Was Simply Impossible for Her to Understand Keynes’s Theory

22 Pages Posted: 12 Feb 2020

Date Written: January 18, 2020

### Abstract

Keynes discovered in correspondence with Joan Robinson in the September-October-November, 1936 time period that she did not have the technical knowledge of economics or mathematics that was needed in order to be able to grasp and understand his General Theory, which revolved around his Liquidity Preference theory of the rate of interest.

Joan Robinson could understand simple constructs like q = f(p), M=L(r) , I=f(r) or if Y=C +I and Y= C+S, then I=S. However, she could not follow Keynes’s liquidity preference equation on page 199, that M=M1+M2=L1 (r)+L2 (Y)=L, the logical theory of the multiplier on pages 122-123 or the preliminary mathematical presentations on pages 114-115, 137, the definition of uncertainty as an inverse function of the weight of the argument from chapter 6 of the A Treatise on Probability, or the Appendix to chapter 19, chapter 20, or chapter 21 of the General Theory. Joan Robinson repeatedly claimed that because she knew no mathematics, she had to think for herself. However, this claim simply ignores the fact that mathematics or logic is an aid that helps one to think for oneself. In order to avoid questions about Keynes’s D-Z or IS-LM models, she created an “interpretation“ of Keynes that involved a complete misinterpretation of Keynes’s views on uncertainty, so that uncertainty became a state of complete and total uncertainty of the future that meant that no mathematical or statistical modeling was possible. Since it was impossible to mathematically define equations, equilibrium was impossible so that no quantitative, determinate, numerical, equilibrium answer was possible for any system of simultaneous equations concerning the macro economy.The best one could do was to do a ceteris paribus, partial equilibrium, Marshallian approach.

G L S Shackle used these ideas from Joan Robinson to create his own approach to decision making based on a Knowledge, Unknowledge-Certainty, Uncertainty dual ,binary concept that was an all or nothing approach. Either there was a situation of complete certainty, which was knowledge or there was a situation of no knowledge or complete uncertainty. This completely rejects Keynes’s logical construct of the weight of the argument and the existence of probable knowledge, so that both Robinson and Shackle, as well as all heterodox schools of thought, completely rejected Keynes’s own definition of uncertainty that he provided on page 148 in footnote 1 in chapter 12 of the General Theory.

Contrary to Keynes ,probability was not the guide to life for Robinson simply because no probabilities existed because there was no probable knowledge of the future.

**Keywords:** Robinson, Keynes IS-LM D-Z, Bastard Keynesianism

**JEL Classification:** B10, B12, B14, B18, B20, B22

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