Neither Keynes Himself, Nor Those of His Colleagues Who Influenced Him, Had Really Grasped the "Law of Markets"

Keynes' own reference to the law was based upon a quotation, not from Say's own enunciation, but from a rather unsatisfactory exposition of the idea in J. S. Mill's Principles of Political Economy; and the passage Keynes quoted was torn from a context which throws essential light upon its implications. The young economists at Cambridge whose outlook Keynes found congenial and with whom he discussed his developing ideas, must surely have been unaware of Mill's incomparably more satisfactory treatment of the same topic in his Unsettled Questions in Political Economy, or they could hardly have failed to draw his attention to it. I feel even more certain that they could not have been aware of James Mill's astonishing Commerce Defended (1808) which is a better exposition of Say's law than Say's original enunciation of it. My own judgment is that neither Keynes himself, nor those of his colleagues who influenced him, had really grasped the "law of markets" to which Say's name has become attached.

--William H. Hutt, A Rehabilitation of Say's Law (Athens, OH: Ohio University Press, 1974), 24-25.