 This is true only in two cases. First, when assuming that all other circumstances, especially the rate of surplus-value, remain unchanged there is a change in the value of that commodity which is a money-commodity. (The same occurs in a merely nominal change of value, the rise or fall of more tokens of value, other conditions being equal.) Let the total capital = 100, and the profit = 20, the rate of profit being = 20%. Should gold fall by half, or double, the same capital previously worth only 100, will be worth 200 if it falls and the profit will be worth 40, i. e., it will be expressed in so much money instead of the former 20; if it rises, the capital of 100 will be worth only 50, and the profit will be represented by a product, whose value will be 10. But in either case 200:40 = 50:10 = 100:20 = 20%. In all these examples there would, however, have been no actual change in the magnitude of capital-value, and only in the money-expression of the same value and the same surplus-value. For this reason s/C, or the rate of profit, could not be affected. In the second case there is an actual change of magnitude in the value, but unaccompanied by a change in the ratio of v to c; in other words, with a constant rate of surplus-value the relation of capital invested in labour-power (variable capital considered as an index of the amount of labour-power set in motion) to the capital invested in means of production remains the same. Under these circumstances, no matter whether we have C, or nC, or C/n, e.g., 1,000, or 2,000, or 500, and the rate of profit being 20%, the profit = 200 in the first case, = 400 in the second, and = 100 in the third. But 200:1,000 = 400:2,000 = 100:500 = 20%. That is to say, the rate of profit is unchanged, because the composition of capital remains the same and is not affected by the change in magnitude. Therefore, an increase or decrease in the amount of profit shows merely an increase or decrease in the magnitude of the invested capital. In the first case there is, therefore, but the appearance of a change in the magnitude of the employed capital, while in the second case there is an actual change in magnitude, but no change in the organic composition of the capital, i. e., in the relative proportions of its variable and constant portions. But with the exception of these two cases, a change in the magnitude of the employed capital is either the result of a preceding change in the value of one of its components, and therefore of a change in the relative magnitude of these components (as long as the surplus-value itself does not change with the variable capital); or, this change of magnitude (as in labour-processes on a large scale, introduction of new machinery, etc.) is the cause of a change in the relative magnitude of its two organic components. In all these cases, other circumstances remaining the same, a change in the magnitude of the employed capital must therefore be accompanied simultaneously by a change in the rate of profit. Fluctuations in the rate of profit may occur irrespective of changes in the organic components of the capital, or of the absolute magnitude of the capital, through a rise or fall in the value of the fixed or circulating advanced capital caused by an increase or a reduction of the working-time required for its reproduction, this increase or reduction taking place independently of the already existing capital. The value of every commodity thus also of the commodities making up the capital is determined not by the necessary labour-time contained in it, but by the social labour-time required for its reproduction. This reproduction may take place under unfavourable or under propitious circumstances, distinct from the conditions of original production. If, under altered conditions, it takes double or, conversely, half the time, to reproduce the same material capital, and if the value of money remains unchanged, a capital formerly worth 100 would be worth 200, or 50 respectively. Should this appreciation or depreciation affect all parts of capital uniformly, then the profit would also be accordingly expressed in double, or half, the amount of money. But if it involves a change in the organic composition of the capital, if the ratio of the variable to the constant portion of capital rises or falls, then, other circumstances remaining the same, the rate of profit will rise with a relatively rising variable capital and fall with a relatively falling one. If only the money-value of the advanced capital rises or falls (in consequence of a change in the value of money), then the money-expression of the surplus-value rises, or falls, in the same proportion. The rate of profit remains unchanged.
Economic Manuscripts: Capital, Vol.3, Chapter 7