Karl Marx,
Das Kapital
(1906)
“ Just as little as the commodities that the capitalist buys with a part of the surplus-value for his own consumption, serve the purpose of production and of creation of value, so little is the labour that he buys for the satisfaction of his natural and social requirements, productive labour. Instead of converting surplus-value into capital, he, on the contrary, by the purchase of those commodities and that labour, consumes or expends it as revenue. ”
