Horkheimer was a self-declared Marxist who favored Schopenhauer over Lukács and the interpretative school.

Evidence

A passage from Korsch’s Marxism and Philosophy might occur to someone who saw Horkheimer sitting in front of this picture and who heard him referring in conversation to Schopenhauer as one of his most important influences. Korsch had written that one would have to regard Marxism (as the Marxist theoreticians of the Second International had done) as not implying specific attitudes to philosophical questions, for it not to seem an impossibility that a leading Marxist theoretician could in private life be a supporter of the philosophy of Arthur Schopenhauer'. … Strzelewicz's impression was that Horkheimer was a middle-class philosopher who was close to Marxism and communism, who was half neo-Kantian, half positivist, a lecturer who enjoyed open discussions, who seldom mentioned Marx by name, and who thought just as little of Lukács's Marxism as of the interpretative’ philosophy of Adorno and Benjamin. — Rolf Wiggershaus, The Frankfurt School, 204

Categorization

• XREF: Connects to Horkheimer’s later project in Dialectic of Enlightenment, where pessimism about instrumental reason (Schopenhauerian strain) and Marxist critique intertwine. — connects to: Rousseau and Kant prepared the doctrine Schopenhauer first proclaimed pure. — Bertrand Russell, History of Western Philosophy, 2752; Will-primacy doctrine, not pessimism, is Schopenhauer’s most influential legacy. — Bertrand Russell, History of Western Philosophy, 2752

Broader Connections

• Rousseau and Kant prepared the doctrine Schopenhauer first proclaimed pure. #corroborates (0.75) — Bertrand Russell, History of Western Philosophy, 2752
• Will-primacy doctrine, not pessimism, is Schopenhauer’s most influential legacy. #expands (0.70) — Bertrand Russell, History of Western Philosophy, 2752