Of all the classes that stand face to face with the bourgeoisie to-day, the proletariat alone is a really revolutionary class. The other classes decay and finally disappear in the face of modern industry; the proletariat is its special and essential product.
1848 February, Karl Marx, Frederick Engels [i.e., Friedrich Engels], “Bourgeois and Proletarians”, in Samuel Moore, transl., Manifesto of the Communist Party. […], 2nd edition, New York, N.Y.: National Executive Committee of the Socialist Labor Party, published 1898, page 27