Social democracy.. is only the advance guard of the proletariat, a small piece of the total working masses; blood from their blood, and flesh from their flesh.

History is the only true teacher, the revolution the best school for the proletariat.

The high stage of world-industrial development in capitalistic production finds expression in the extraordinary technical development and destructiveness of the instruments of war.

Freedom is always the freedom of dissenters.

With the true artist, the social formula that he recommends is a matter of secondary importance; the source of his art, its animating spirit, is decisive.

Without general elections, without freedom of the press, freedom of speech, freedom of assembly, without the free battle of opinions, life in every public institution withers away, becomes a caricature of itself, and bureaucracy rises as the only deciding factor.

Before a revolution happens, it is perceived as impossible; after it happens, it is seen as having been inevitable.