The trouble is already there to see. Imagine an economy consisting of a single firm which has bought means of production and labour power for a total of $100, in order to produce a mass of commodities it intends to sell for $110, i.e. at a profit of 10 per cent. The problem is that the firm’s suppliers of constant and variable capital are also its only potential customers. Even if the would-be buyers pool their funds, they have only their $100 to spend, and no more. Production of the total supply of commodities exceeds the monetarily effective demand in the system. As Harvey explains in The Limits to Capital, effective demand ‘is at any one point equal to C+V, whereas the value of the total output is C+V+S. Under conditions of equilibrium, this still leaves us with the problem of where the demand for S, the surplus value produced but not yet realised through exchange, comes from.’ An extra $10 in value must be found somewhere, to be exchanged with the firm if it is to realise its desired profit.
Benjamin Kunkle has a fine review of David Harvey‘s recent book the Enigma of Capital, in which he also broadly reviews related literature by classical Marxist authors, including John Bellamy Foster’s Ecological Rift: Capitalism’s War on Earth.