Capital, Volume Three: The Process of Capitalist Production as a Whole by Karl Marx

The purely technical movements performed by money in the circulation process of industrial, and, as we may now add, of commercial capital (since it takes over a part of the circulation movement of industrial capital as its own, peculiar movement), if individualised as a function of some particular capital performing just these, and only these, operations as its specific operations, convert this capital into money-dealing capital. A portion of industrial capital, and, more precisely, also of commercial capital, not only obtains all the time in the form of money, as money-capital in general, but as money-capital engaged precisely in these technical functions. A definite part of the total capital dissociates itself from the rest and stands apart in the form of money-capital, whose capitalist function consists exclusively in performing these operations for the entire class of industrial and commercial capitalists. As in the case of commercial capital, a portion of industrial capital engaged in the circulation process in the form of money-capital separates from the rest and performs these operations of the reproduction process for all the other capital. The movements of this money-capital are, therefore, once more merely movements of an individualised part of industrial capital engaged in the reproduction process.

It is only when, and in so far as, capital is newly invested – which also applies to accumulation – that capital in money-form appears as the starting-point and the end result of the movement. But for all capitals already engaged in the process, these first and last points appear merely as points of transit. Since, as already seen in the case of simple commodity-circulation, from the moment of leaving the sphere of production to the moment of its re-entry industrial capital undergoes the metamorphosis C' – M – C, M in fact represents the end result of one phase of the metamorphosis, just to become the starting-point of the reverse phase, which supplements it. And although the C – M of industrial capital is always M – C – M for merchant's capital, the actual process for the latter is continually also C – M – C once it has begun to function. But it performs the acts C – M and M – C simultaneously. This is to say that there is not just one capital in the stage C – M while another is in the stage M – C, but that the same capital buys continually and sells continually at one and the same time because of the continuity of the production process. It is to be found always in both stages at one and the same time. While one of its parts turns into money, later to be reconverted into commodities, another turns simultaneously into commodities, to be reconverted into money.