Keynes, J.M. “A Reply to Dr. Hayek.” Economica 12 (November 1931): 387–397.
“In an article recently published, Dr. Hayek has invited me to clear up some ambiguities of terminology which he finds in my Treatise of Money, and also other matters. As he frankly says, he has found his difference with me difficult to explain. He is sure that my conclusions are wrong (though he does not clearly state which conclusions), but he finds it ‘extremely difficult to demonstrate the exact point of disagreement and to state his objections.'”