A casual survey of Adorno's writings on music could well give the impression that his theoretical concerns emerged fully formed in the 1920s and did not change substantially thereafter. There is some truth in Friedemann Grenz's observation that ‘Adorno's thought had remained always constant, without periods of change, that there had been no development in it’ Indeed, the unity of thought throughout his work is striking, and there are evident connections between even the most occasional of the early pieces and the large-scale philosophical writings of his last years. Nevertheless, there is also a sense in which Adorno's work does show development over time. It moves from the early non-Marxian writings to an idiosyncratic reception of Marx and Hegel influenced by the neo-Marxism of Lukacs and by the attempt of the Frankfurt School to bring about a fusion of Marx and Freud. In addition, Adorno's emigration years in the United States were marked by an abrupt encounter with empirical sociology and psychology, while the period of his return to Frankfurt in the post-war years was characterized by a certain consolidation in his philosophical and critical method in works like Negative Dialektik and Ästhetische Theorie. All these developments have implications for his aesthetics of music.