The problem to be resolved is as follows. The owner of money has to buy his commodities at their value, and to sell them at their value, and nevertheless at the end of the process to realise a surplus. This is the end and aim of his existence as a capitalist, and if he does not accomplish it, he is as a capitalist a failure. So that his development from the mere money-owner to the full-blown capitalist has to take place at once within the sphere of circulation and without it: 236 that is, he must follow the law of the exchange of commodities, and nevertheless must act in apparent contradiction to that law. This problem cannot be solved merely by means of the money which he owns, the value of which is, so to say, petrified. As Ricardo says, “In the form of money, capital has no profit.” As money, it can only be hoarded.
Neither can the surplus originate in the mere re-sale of the commodity, “which does no more than transform the article from its bodily form back into its money-form.” The only alternative left is that the change should originate in the use-value of the article bought with the money in the first instance, and on which the capitalist has to operate.
“In order to be able to extract value from the consumption of a commodity, our friend Moneybags must be so lucky as to find within the sphere of circulation, in the market, a commodity whose use-value possesses the peculiar property of being a source of value, whose actual consumption therefore is itself an embodiment of labour, and, consequently, 237 creation of value. The possessor of money does find on the market such a special commodity in capacity of labour, or labour-power.”
By labour-power or the capacity of labour Marx understands the whole of the mental and physical capacities in a human being which are brought into action in the production of commodities; in short, the man and all that is in him as a wealth-producing machine.