But in this case there has been no increase of value; the value has merely changed hands; Peter has £10 more than he had before, and Paul £10 less. The commodities have between them after the transaction, as they had before it, a total value of £90, and that total cannot be increased by a mere change of possessor. Having thus established to his satisfaction that commerce, being only a series of exchanges, cannot produce any increase of value, or what he terms surplus value, Marx says that that only makes the problem of the origin of surplus value more enigmatical than ever. For we are thus left in presence of an apparent contradiction: surplus value cannot spring up in the circulation of commodities because circulation is nothing but an exchange of equivalents; and yet surplus value cannot spring up anywhere except in circulation, because the class of persons who receive it and live by it do not produce. Here, then, is a riddle, and Marx sets himself to rede it. True, he says, value is not created directly in the market, but a commodity is purchased in the market which has the remarkable property of creating value. That commodity is the human powers of labour. The very use of these powers, their consumption, their expenditure, is the creation of value. But marvellous as they are, their possessor is obliged to sell them, because while they are yielding their product he must meanwhile live, and he sells a day's use of them for a day's means of living. They create in a day far more than the value of the wages for which they are bought. This excess is surplus value, and is the secret and fountainhead of all accumulations of capital. Powers which can create six shillings worth in a day may be procured in the market for three shillings, because three shillings will pay for their necessary maintenance. Surplus value is the difference between the value of the labourer's necessary maintenance and the value of the labourer's production, and it is in the present system entirely appropriated by the dealer who advances him his wages.