Eclipse of Reason was jointly authored with Adorno though published under Horkheimer alone

Evidence

These lectures were designed to present in epitome some aspects of a comprehensive philosophical theory developed by the writer during the last few years in association with Theodore [sic] W. Adorno. It would be difficult to say which of the ideas originated in his mind and which in my own; our philosophy is one. — Rolf Wiggershaus, The Frankfurt School, 1452

Categorization

• XREF: Illustrates the co-authorship pattern of the Horkheimer-Adorno partnership, also visible in Dialectic of Enlightenment itself.