The employer can make use of labour power so long that it not only creates its own exchange value (the value of the means of subsistence), but double this. To create the value of wages, the worker needs five or six hours daily, but he is obliged to produce for the capitalist during ten or twelve hours. If the worker were independent he would only produce during one half of the working day in order to receive his means of subsistence. This period of producing Marx called "necessary labour." As he is dependent on the capitalist, the worker must not only perform "necessary labour" but also surplus labour: the worker can generally only find employment under the conditions that, besides the time needed for himself, he also works a definite number of hours for the capitalist without payment. Or, as Marx says: "The fact that half a day's labour is necessary to keep the labourer alive during the 24 hours, does not in any way prevent him from working the whole day. Therefore, the value of labour power and the value which labour creates in the labour process are two entirely different magnitudes. And this difference in the two values was what the capitalist had in view when he was purchasing labour power. 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." "No injury to the seller," which is quite correct from the standpoint of Ricardo, but not from that of Marx. He often calls surplus value "unpaid labour," and says, for example, "the capitalist appropriates one half of every day's labour without payment." In other words, he takes away something without return. This is a very distinct ethical judgment. On the other hand, it is very important that in our consideration of the wages question we have come up against the Marxian doctrine of surplus value. For this doctrine is the cornerstone of the whole economic system of Marx. 4. _Surplus Value._ We have already noted that Marx followed the classical economics in his treatment of the theory of value, but improved the definition of it, and brought it to bear on wages. In doing this he laid stress on the conflict between Capital and Labour. The beginning of this dialectical process, so far as England was concerned, was the work of the anti-capitalistic critics, who uttered their protest about 1820, or three years after the appearance of Ricardo's work. They declared, according to Ricardo, labour is the source and the measure of value. And yet according to his opinion labour is nothing and capital everything.