The interest.

We have so far only considered the movements of loaned capital between its owner and the industrial capitalist. Now we must inquire into interest.

The lender expends his money as capital; the amount of value, which he relinquishes to another, is capital, and consequently returns to him. But the mere return of it would not be the reflux of the loaned sum of value as capital, but merely the return of a loaned sum of value. To return as capital, the advanced sum of value must not only be preserved in the movement but must also expand, must increase in value, i.e., must return with a surplus-value, as M + DM, the latter being interest or a portion of the average profit, which does not remain in the hands of the operating capitalist, but falls to the share of the money-capitalist.

What does the money-capitalist give to the borrower, the industrial capitalist? What does he really turn over to him? It is only this act of handing over money which changes lending money into alienation of money as capital, i.e., alienation of capital as a commodity.

What, now, is the use-value which the money-capitalist gives up for the period of the loan and relinquishes to the productive capitalist — the borrower? It is the use-value which the money acquires by being capable of becoming capital, of performing the functions of capital, and creating a definite surplus-value, the average profit (whatever is above or below it appears here as a mere accident) during its process, besides preserving its original magnitude of value. In the case of the other commodities the use-value is ultimately consumed. Their substance disappears, and with it their value. In contrast, the commodity-capital is peculiar in that its value and use-value not only remain intact but also increase, through consumption of its use-value.

It is this use-value of money as capital — this faculty of producing an average profit — which the money-capitalist relinquishes to the industrial capitalist for the period, during which he places the loaned capital at the latter's disposal.