I remember a speech Gary North gave where he talked about Friedman’s statement that “We’re all keynesians now”. Later Friedman elaborated with saying that he meant methodologically. North then said that “that was kind of the problem”.
In what sense then did Keynes change the method that existed before him and after. I know post-keynesians argue that Keynes didn’t advocated the mathematical approach. So was it keynes directly or was it his followers? Or was the idea of positivism in economics?