The article investigates one of the most infrequently discussed works in Theodor Adorno's philosophical corpus: "The Concept of the Unconscious in the Transcendental Theory of the Psyche." Designed for acceptance as a Habilitation thesis in 1926-1927 but then withdrawn, the text is often categorized as an account of the philosophical system proposed by Adorno's teacher Hans Cornelius and hence of minor importance for Adorno's mature works. The author, however, contends that "The Concept of the Unconscious" casts an interesting light on the historical origins and the conceptual foundations of the relation between society and psyche, which Adorno dealt with theoretically in the later course of his intellectual career. In fact, he asserts, it set the stage for Adorno's lifelong engagement with Freud and psychoanalysis. The author argues that here Adorno maps out a dual critique of the prevailing neo-Kantian and vitalist views of the unconscious, turning to Freud for a more appropriate interpretation of the unconscious as a product of the interplay between psychological and social processes. He then further developed this dialectical understanding of psychosocial relations in numerous postwar writings on the subject of psychoanalysis.