A class of labourers, who live only so long as they find work, and who find work only so long as their labour increase capital. These labourers, who must sell themselves piecemeal, are a commodity, like every other article of commerce, and are consequently exposed to all the vicissitudes of competition, to all the fluctuations of the market.

Section 1, paragraph 30, lines 3-8. - The Manifesto of the Communist Party (1848)