"As capitalist, he is only capital personified. His soul is the soul of capital. But capital has one single life impulse, the tendency to create value and surplus-value, to make its constant factor, the means of production, absorb the greatest possible amount of surplus-labour.

"Capital is dead labour, that, vampire-like, only lives by sucking living labour, and lives the more, the more labour it sucks. The time during which the labourer works, is the time during which the capitalist consumes the labour-power he has purchased of him.

"If the labourer consumes his disposable time for himself, he robs the capitalist.

[…]

"It must be acknowledged that our labourer comes out of the process of production other than he entered. In the market he stood as owner of the commodity 'labour-power' face to face with other owners of commodities, dealer against dealer. The contract by which he sold to the capitalist his labour-power proved, so to say, in black and white that he disposed of himself freely. The bargain concluded, it is discovered that he was no 'free agent,' that the time for which he is free to sell his labour-power is the time for which he is forced to sell it, that in fact the vampire will not lose its hold on him 'so long as there is a muscle, a nerve, a drop of blood to be exploited.' For 'protection' against 'the serpent of their agonies,' the labourers must put their heads together, and, as a class, compel the passing of a law, an all-powerful social barrier that shall prevent the very workers from selling. by voluntary contract with capital, themselves and their families into slavery and death."

— Karl Marx, Capital, vol 1