Adorno's work in the years before his death was shaped by the idea of "negative dialectics", set out especially in his book of that title. A key notion in the work of the Frankfurt School since "Dialectic of Enlightenment" had been the idea of thought becoming an instrument of domination that subsumes all objects under the control of the (dominant) subject, especially through the notion of identity, i.e. of identifying as real in nature and society only that which harmonized or fit with dominant concepts, and regarding as unreal or non-existent everything that did not. Adorno's "negative dialectics" was an attempt to articulate a non-dominating thought that would recognize its limitations and accept the non-identity and reality of that which could not be subsumed under the subject's concepts. Indeed, Adorno sought to ground the critical bite of his sociological work in his critique of identity, which he took to be a reification in thought of the commodity form or exchange relation which always presumes a false identity between different things. The potential to criticise arises from the gap between the concept and the object, which can never go into the former without remainder. This gap, this non-identity in identity, was the secret to a critique of both material life and conceptual reflection.