" The anarchist sets two sources of revolutionary energy against the constraints and hierarchies of authoritarian socialism: the individual, and the spontaneity of the masses. Some anarchists are more individualistic than social, some more social than individualistic. However, one cannot conceive of a libertarian who is not an individualist."
As a youth, Guérin was attracted to the radical movement, and was won over to revolutionary socialism as espoused by Leon Trotsky. As a member of the Trotskyist movement, he wrote Fascism and Big Business, one of the premier texts in the always-pugnacious battle over that term's definition. Like Victor Serge, as Guerin grew older, his politics moved increasingly leftward, leading him later in life to espouse a hybrid of anarchism and marxism. Arguably, his most important book from this period of his life is Anarchism: From Theory to Practice, which includes an introduction by Noam Chomsky. Extremely prolific in French, it's unfortunate that, outside of the books above and a few small pamphlets, most of this thinker's original and stimulating material is unavailable in English (a pamphlet, "Libertarian Marxism?", which includes two singular essays, is also available in English at this time).
source : http://dwardmac.pitzer.edu/Anarchist_Archives/bright/guerin/guerinbio.html
