Western philosophy since Descartes has been haunted by the question of how a self-enclosed subject can know an external world. The idealist resolution — from Berkeley through Kant to Hegel — was to make the object in some sense a product of the subject: the world as we know it is constituted by the categories of mind, the forms of intuition, the self-movement of Spirit. Adorno regards this resolution as both philosophically insufficient and ideologically suspect: it makes the world the mirror of the subject, projecting human domination onto the very structure of knowledge.
The preponderance of the object does not mean that subjects are unimportant or that the world is simply given independently of all conceptual mediation. It means that objects always exceed their concepts — that there is always more to the particular than any general category captures. This excess is not a defect of our knowledge but an ontological fact: the non-identity of concept and object is not a failure of thinking but thinking's most important achievement, the moment at which thought acknowledges rather than suppresses what resists it.
Adorno's insistence on the preponderance of the object is a form of materialism, but a self-reflective one. He does not claim that we have unmediated access to a material world independent of all conceptual framing. He claims instead that the concept of matter — the resistant, non-identical givenness of things — must be preserved within idealism itself as its corrective. The task is to think through the subject-object relation in a way that does justice to both sides: neither reducing the object to the subject (idealism) nor reducing the subject to a passive mirror of the object (naïve realism).
The discussion of the preponderance of the object occupies the third section of the introduction to Negative Dialectics (1966), "On Subject and Object." The concept is central to Adorno's later essays, especially "Subject and Object" in The Positivism Dispute in German Sociology.