The Classical School define them as the decisive factors for economic activity. Instead, Keynes emphasises that statements about the barter economy are not necessarily transferable to the monetary economy. Despite this, he does not intend a total break from classical and neoclassical theory but aims to complete the barter theory the Classical School. Keynes interprets that school, as a specific case of his General Theory which only deals with the unusual state of full employment. A general theory of the economy should also analyse phenomena such as business cycles, crises, and unemployment in which money and interest are important factors.
In the General Theory, which indeed is also a theory of the rate of interest and money, one can-surprisingly-not find an analysis which really sheds light on the differences between barter and monetary economy. Keynes shows a non-elaborated theorem, which he believes to be capable of overcoming the false dichotomy of economic theory between value theory and monetary theory. Its central argument is that 'the importance of money essentially flows from its being a link between the present and the future.' But this only happens at the end of his theory of employment, developed in books I to IV of the General Theory.