Dialectic in Western Marxism

The fundamental principles of modern dialectical philosophy derive from Hegel. He sums them up as follows. `Everything is inherently contradictory ... Contradiction is the root of all movement and vitality, it is only in so far as something has a contradiction within it that it moves, has an urge and activity' (Hegel 1969, 439). In Hegel's philosophy these ideas form part of an all-embracing idealist system which portrays all phenomena both natural and social as subject to dialectic. Marx inherits and transforms these ideas; but how precisely he does so has been a topic of much dispute within western Marxism. Marx himself describes his relation to Hegel with the aid of a couple of graphic but vague metaphors. He says that he turns Hegel's dialectic `right side up' in order to `discover the rational kernel within the mystical shell' (Marx 1961, 20). But how can this be done? Is there a `rational kernel' to Hegel's dialectic? If so, how can it be extracted?