Adorno refuses the aesthetic sentimentalism that treats art as a matter of mere feeling or the aesthetic formalism that treats it as pure play of form with no cognitive significance. Art is a form of cognition — but cognition of a kind that discursive thought cannot achieve. Where philosophy and science must make their objects explicit, subject them to argumentative scrutiny, and reduce them to communicable propositions, art can preserve in its form what cannot be said — the non-identical remainder, the contradiction that has not been resolved, the suffering that has not found adequate expression.
Art's truth content is not a property of individual subjectivity — it is not simply the expression of the artist's feelings or experiences. It is, rather, what the work registers of the objective social world — the tensions, contradictions, and possibilities that are present in the historical moment in which the work is made. The greatest works do not simply reflect their social moment but crystallise it — making visible what the culture of the time suppresses or fails to articulate. This is why art's truth content is accessible only through critical interpretation, not through immediate aesthetic experience.
Adorno identifies two opposed principles at work in art: mimesis and rationality. Mimesis — the capacity for assimilation, for making oneself like the other, for receptive openness to the object — is what enables art to register what exceeds the concept. Rationality — formal organisation, consistency, the drive to unified composition — is what gives art its intelligibility and its capacity to communicate. The tension between these two principles is constitutive of art: too much mimesis and the work dissolves into formless expression; too much rationality and it becomes mere schema. The truth content of authentic art arises precisely from this unresolved tension.
The concept of Wahrheitsgehalt (truth content) is developed throughout Aesthetic Theory (1970) and in Adorno's essay on Valéry and Proust, "On Lyric Poetry and Society," collected in Notes to Literature. It was the subject of intense debate between Adorno and Walter Benjamin in the 1930s.
