In my political economy course, my teacher said that Keynes discovered that money was not neutral, meaning that a change in the money supply has effects on production.
Increase in money supply -> lower interest rates -> more investment -> more production
In 1912 Mises published his “Theory of Money and Credit” in which he explains ABCT. According to ABCT an increase in the money supply leads to lower interest rates which generates an artificial boom. So Mises knew that money was not neutral. So was Keynes really the first economist to discover this fact?
Richard Cantillon wrote about the non-neutrality of money in the first full treatise ever written on economics. Here is a new translation of the work, written in the early 1730s and published posthumously in 1755: