A drop in the rate of profit is attended by a rise in the minimum capital required by an individual capitalist for the productive employment of labour; required both for its exploitation generally, and for making the consumed labour-time suffice as the labour-time necessary for the production of the commodities, so that it does not exceed the average social labour-time required for the production of the commodities. Concentration increases simultaneously, because beyond certain limits a large capital with a small rate of profit accumulates faster than a small capital with a large rate of profit. At a certain high point this increasing concentration in its turn causes a new fall in the rate of profit. (Karl Marx, Capital, Volume 3, Chapter 15)
The problem of prices and profit and of the relation between the two, which has bedeviled the simpleton economist for two hundred years, has reared its ugly head again in a series of posts amounting to a food fight among bourgeois simpletons. The question raised in the exchanges, which I have previously covered here, involves the question of the source of profits in the capitalist mode of production and the interrelation between profit and prices.
At stake is far more than is apparent in the obscure criticism raised by heterodox economists against the mainstream neoclassical school that the neoclassical school wants to determine profit by the marginal productivity of capital, and then calculate the quantity of capital in part by asking how profitable it is to own the capital goods. If prices and profit are dependent on each other in this way it calls into question the historical trajectory of the mode of production itself.