Hello, if you would please refer to "Wage labour and capital":

We have just seen how the fluctuation of supply and demand always bring the price of a commodity back to its cost of production. The actual price of a commodity, indeed, stands always above or below the cost of production; but the rise and fall reciprocally balance each other, so that, within a certain period of time, if the ebbs and flows of the industry are reckoned up together, the commodities will be exchanged for one another in accordance with their cost of production. Their price is thus determined by their cost of production.

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What, then, is the cost of production of labour-power?

It is the cost required for the maintenance of the labourer as a labourer, and for his education and training as a labourer.

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Thus, the cost of production of simple labour-power amounts to the cost of the existence and propagation of the worker. The price of this cost of existence and propagation constitutes wages. The wages thus determined are called the minimum of wages. This minimum wage, like the determination of the price of commodities in general by cost of production, does not hold good for the single individual, but only for the race. Individual workers, indeed, millions of workers, do not receive enough to be able to exist and to propagate themselves; but the wages of the whole working class adjust themselves, within the limits of their fluctuations, to this minimum.

The price of education can only fall once the supply of laborer requiring said education falls below the demand of such laborers and, consequently, the price of their labor power rises above the cost of creating this labor power. The (even more) bad news is:

But the productive forces of labour is increased above all by a greater division of labour and by a more general introduction and constant improvement of machinery. The larger the army of workers among whom the labour is subdivided, the more gigantic the scale upon which machinery is introduced, the more in proportion does the cost of production decrease, the more fruitful is the labour.

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Furthermore, to the same degree in which the division of labour increases, is the labour simplified. The special skill of the labourer becomes worthless. He becomes transformed into a simple monotonous force of production, with neither physical nor mental elasticity. His work becomes accessible to all; therefore competitors press upon him from all sides. Moreover, it must be remembered that the more simple, the more easily learned the work is, so much the less is its cost to production, the expense of its acquisition, and so much the lower must the wages sink – for, like the price of any other commodity, they are determined by the cost of production.