The fact that only six hours' labour is necessary to keep the labourer alive for twenty-four hours, does not in any way prevent him from working twelve hours out of the twenty-four. The value of the labour-power, and the value which that labour-power creates in the labour-process, are two different magnitudes. 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 whole day's labour. The circumstance that the value which the use of it during one day creates is double its own value for a day is a piece of especially good luck for the buyer, but according to the laws of exchange of commodities by no means an injustice to the seller. On our assumption, therefore, the labourer each day costs the owner of money the value of the product of six hours' labour, but he hands over to him each day the value of the product of twelve hours' labour. The difference in favour of the owner of the money is six hours of unpaid surplus-labour, a surplus-product for which he does not pay and in which six hours' labour is embodied. The trick has been performed. Surplus-value has been produced; money has been converted into capital.