Both for the production on a ...

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.
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

Quotes from the same author

Under private property, each tries to establish over the other an alien power, so as thereby to find satisfaction of his own selfish need. The increase in the quantity of objects is therefore accompanied by an extension of the realm of the alien powers to which man is subjected, and every new product represents a new potentiality of mutual swindling and mutual plundering.
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 Karl Marx
The wealthy man is the man whois much, not the one who has much
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 Karl Marx
The ruling ideas of each age have ever been the ideas of its ruling class.
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 Karl Marx
Labour is ... not the only source of material wealth, i.e, of the use-values it produces. As William Petty says, Labour is the father of material wealth, the earth is its mother.
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 Karl Marx
The social principles of Christianity preach cowardice, self-contempt, abasement, submission, humility, in a word all the qualities of the canaille
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 Karl Marx