"Marxist theory offers us a reliable instrument enabling us to recognize and combat typical manifestations of opportunism. But the socialist movement is a mass movement. Its perils are not the product of the insidious machinations of individuals and groups. They arise out of unavoidable social conditions. We cannot secure ourselves in advance against all possibilities of opportunist deviation. Such dangers can be overcome only by the movement itself – certainly with the aid of Marxist theory, but only after the dangers in question have taken tangible form in practice."