Let us examine the matter more closely. The value of a day’s labour-188power
 amounts to 3 shillings, because on our assumption half a day’s labour is
 embodied in that quantity of labour-power, i.e., because the means
 of subsistence that are daily required for the production of labour-power,
 cost half a day’s labour. But the past labour that is embodied in the labour-power,
 and the living labour that it can call into action; the daily cost of maintaining
 it, and its daily expenditure in work, are two totally different things.
 The former determines the exchange-value of the labour-power, the latter
 is its use-value. The fact that half a day’s labour is necessary to keep
 the labourer alive during 24 hours, does not in any way prevent him from
 working a whole day. Therefore, the value of labour-power, and the value
 which that labour-power creates in the labour-process, are two entirely
 different magnitudes; and this difference of the two values was what the
 capitalist had in view, when he was purchasing the labour-power. The useful
 qualities that labour-power possesses, and by virtue of which it makes
 yarn or boots, were to him nothing more than a conditio sine qua non; for
 in order to create value, labour must be expended in a useful manner. What
 really influenced him was the specific use-value which this commodity possesses
 of being a source not only of value, but of more value than it has itself.
 This is the special service that the capitalist expects from labour-power,
 and in this transaction he acts in accordance with the “eternal laws” of
 the exchange of commodities. The seller of labour-power, like the seller
 of any other commodity, realises its exchange-value, and parts with its
 use-value. He cannot take the one without giving the other. The use-value
 of labour-power, or in other words, labour, belongs just as little to its
 seller, as the use-value of oil after it has been sold belongs to the dealer
 who has sold it. The owner of the money has paid the value of a day’s labour-power;
 his, therefore, is the use of it for a day; a day’s labour belongs to him.
 The circumstance, that on the one hand the daily sustenance of labour-power
 costs only half a day’s labour, while on the other hand the very same labour-power
 can work during a whole day, that consequently the value which its use
 during one day creates, is double what he pays for that use, this circumstance
 is, without doubt, a piece of good luck for the buyer, but by no means
 an injury to the seller.