Keynes' general theory : structure, substance and contradiction

In The General Theory of Employment, Interest and Money, John Maynard Keynes bequeathed to economics a macro-theory of fluctuating sub-optimality. The theory is composed of a set of functional relations and 'unorthodox' substantive psychological and social content. The functional relations form a skeletal frame explaining how an economy can settle at a level of output below full employment. The substantive psychological and social content, especially as it relates to investors, imbues that equilibrium with inherent fragility and instability. The theory's internal coherence however is questionable. Because the substance of the theory includes large scale durable investments, this renders relevant cost-competition based on technical change, but that in turn undermines the key functional relations of its original structure.