October 11

Both for the production on a mass scale of this communist consciousness, and for the success of the cause itself, the alteration of men on a mass scale is, necessary, an alteration which can only take place in a practical movement, a revolution; this revolution is necessary, therefore, not only because the ruling class cannot be overthrown in any other way, but also because the class overthrowing it can only in a revolution succeed in ridding itself of all the muck of ages and become fitted to found society anew.

Karl Marx
from Part I: Feuerbach.
Opposition of the Materialist and Idealist Outlook, Section D: Proletarians and Communism in The German Ideology (1845)