  The concept of the nonidentical, in turn, marks the difference between Adorno's materialism and Hegel's idealism. Although he shares Hegel's emphasis on a speculative identity between thought and being, between subject and object, and between reason and reality, Adorno denies that this identity has been achieved in a positive fashion. For the most part this identity has occurred negatively instead. That is to say, human thought, in achieving identity and unity, has imposed these upon objects, suppressing or ignoring their differences and diversity. Such imposition is driven by a societal formation whose exchange principle demands the equivalence (exchange value) of what is inherently nonequivalent (use value). Whereas Hegel's speculative identity amounts to an identity between identity and nonidentity, Adorno's amounts to a nonidentity between identity and nonidentity. That is why Adorno calls for a “negative dialectic” and why he rejects the affirmative character of Hegel's dialectic (ND 143–61).