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

Merchant's, or trading, capital breaks up into two forms or sub-divisions, namely, commercial capital and money-dealing capital, which we shall now define more closely, in so far as this is necessary for our analysis of capital in its basic structure. This is all the more necessary, because modern political economy, even in the persons of its best exponents, throws trading capital and industrial capital indiscriminately together and, in effect, wholly overlooks the characteristic peculiarities of the former.

The movements of commodity-capital have been analysed in Book II. To take the total capital of society, one part of it – always made up of different elements and even changing in magnitude – always exists in the form of commodities on the market, to be converted into money. Another part exists on the market in the form of money, to be converted into commodities. It is always in the process of this transition, of this formal metamorphosis. Inasmuch as this function of capital in the process of circulation is at all set apart as a special function of a special capital, as a function established by virtue of the division of labour to a special group of capitalists, commodity-capital becomes commercial capital.