The origins of monetary theory lie in the classical economics of Adam Smith and his friends. The two cornerstones of the classical system are say s law (萨伊定律) and the quantity theory. Say's law deals th interest rates, employment, and production The quantity theory explains the role of moneyThe origins of monetary theory lie in the classical economics of Adam Smith and his friends. The two cornerstones of the classical system are Say’s law (萨伊定律) and the quantity theory. Say’s law deals with interest rates, employment, and production. The quantity theory explains the role of money