Keynes Versus Robertson in 1936–1937: Robertson’s Mathematical Illiteracy Prevented Him From Understanding Keynes’s Is-Lm(lp) Model in the General Theory

Abstract

J. M. Keynes versus D. Robertson in 1936-37 pits two opponents, one, J. M. Keynes, a highly skilled, sophisticated, mathematically advanced thinker against another, D. Robertson, who doesn’t have even an elementary background in mathematics at the grammar school level. Basically, the intellectual exchanges that take place are so completely one sided in Keynes’s favor that it is questionable whether anything written by Robertson about Keynes should even be considered worth reading. However, the exchanges do give complete support to Paul Samuelson’s long-range goal of greatly increasing the mathematical sophistication and knowledge of the average economist. Robertson’s performance is simply intellectually horrid. Robertson demonstrates repeatedly in his exchanges with Keynes that he is not able to grasp any type of mathematical analysis involving any mathematical function except a mathematical function with one independent variable and one dependent. Robertson found Keynes’s mathematical analysis to be incomprehensible. He could not understand Keynes’s IS-LM (LP) model because it involved a set of simultaneous mathematical equations in r and Y that he had no capacity to grasp because he was a Marshallian used to using the ceteris paribus assumption at both the micro and macro levels. It was impossible for Robertson to follow Keynes’s theory, even though he constantly sought the mathematical advice and help of first AC Pigou and then Harry Johnson.