Therefore, however much the capitalist mode of appropriation may seem to fly in the face of the original laws of commodity production, it nevertheless arises, not from a violation of these laws but, on the contrary, from their application. Let us make this clear once more by briefly reviewing the consecutive phases of motion whose culminating point is capitalist accumulation.
We saw, in the first place, that the original transformation of a sum of values into capital was achieved in complete accordance with the laws of exchange. One party to the contract sells his labor power, the other buys it. The former receives the value of his commodity, whose use value — labor — is thereby alienated to the buyer. Means of production which already belong to the latter are then transformed by him, with the aid of labor equally belonging to him, into a new product which is likewise lawfully his.
The value of this product includes: first, the value of the means of production which have been used up. Useful labor cannot consume these means of production without transferring their value to the new product…
The value of the new product includes, further, the equivalent of the value of the labor power together with a surplus value. This is so because the value of the labor power — sold for a definite length of time, say a day, a week, etc. — is less than the value created by its use during that time. But the worker has received payment for the exchange value of his labor power and by so doing has alienated its use value — this being the case in every purchase and sale.
The fact that his particular commodity, labor power, possesses the peculiar use value of supplying labor, and therefore of creating value, cannot affect the general law of commodity production. If, therefore, the amount of value advanced in wages is not merely found again in the product, but augmented by surplus value, this is not because the seller has been defrauded, for he has really received the value of his commodity; it is due solely to the fact that this commodity has been used up by the buyer.
The law of exchange requires equality only between exchange values of the commodities given in exchange for one another. From the very outset, indeed, it presupposes a difference between their use values and it has nothing whatever to do with their consumption, which begins only after the contract has been concluded and executed.
Thus the original transformation of money into capital takes place in the most exact accordance with the economic laws of commodity production and with the rights of property derived from them. Nevertheless, the result is:
1. that the product belongs to the capitalist and not to the worker;
2.that the value of this product includes, apart from the value of the capital advanced, a surplus value which costs the worker labor but the capitalist nothing, and which none the less becomes the legitimate property of the capitalist;
3. that the worker has retained his labor power and can sell it anew if he finds another buyer.
[…] Thus the law [of value] is not broken; on the contrary, it gains the opportunity to operate continuously.
Karl Marx, “The Transformation of Surplus Value into Capital”, in Capital, Vol. I, trans. by Ben Fowkes, New York: Penguin, 1990, pp. 730-732.