Keynesians Tell Us That Keynes's Immortal Achievement Consists in the Refutation of Say's Law of Markets

Lord Keynes's main contribution did not lie in the development of new ideas but "in escaping from the old ones," as he himself declared at the end of the Preface to his "General Theory." The Keynesians tell us that his immortal achievement consists in the entire refutation of what has come to be known as Say's Law of Markets. The rejection of this law, they declare, is the gist of all Keynes's teachings; all other propositions of his doctrine follow with logical necessity from this fundamental insight and must collapse if the futility of his attack on Say's Law can be demonstrated.

--Ludwig von Mises, Planning for Freedom: And Twelve Other Essays and Addresses, 3rd ed. (South Holland, IL: Libertarian Press, 1974), 64.