Beiser reviews the commonly held position that Schopenhauer was a transcendental idealist and he rejects it: "Though it is deeply heretical from the standpoint of transcendental idealism, Schopenhauer's objective standpoint involves a form of transcendental realism, i.e. the assumption of the independent reality of the world of experience." (Beiser 2016, p. 40)
Schopenhauer, Arthur. Parerga and Paralipomena, Short Philosophical Essays, Vol. 2, Oxford University Press, 2000, Ch. XII: "Additional Remarks on the Doctrine of the Suffering of the World", § 149, p. 292; Schopenhauer, Arthur. Studies in Pessimism: The Essays. The Pennsylvania State University, 2005, p. 7.
Arthur Schopenhauer, Arthur Schopenhauer: The World as Will and Presentation, Volume 1, Routledge, 2016, p. 211: "the world [is a] mere presentation, object for a subject..."
Lennart Svensson, Borderline: A Traditionalist Outlook for Modern Man, Numen Books, 2015, p. 71: "[Schopenhauer] said that 'the world is our conception'. A world without a perceiver would in that case be an impossibility. But we can—he said—gain knowledge about Essential Reality for looking into ourselves, by introspection. ... This is one of many examples of the anthropic principle. The world is there for the sake of man."
Schopenhauer, Arthur. The World as Will and Representation. Vol.Vol. 1, Book 4. For the philosopher, these accounts of the lives of holy, self-denying men, badly as they are generally written, and mixed as they are with super stition and nonsense, are, because of the significance of the material, immeasurably more instructive and impor tant than even Plutarch and Livy. ... But the spirit of this development of Christianity is certainly nowhere so fully and powerfully expressed as in the writings of the German mystics, in the works of Meister Eckhard, and in that justly famous book Die Deutsche Theologie.{{cite book}}: |volume= has extra text (help)
Howard, Don A. (December 2005), "Albert Einstein as a Philosopher of Science"(PDF), Physics Today, 58 (12), American Institute of Physics: 34–40, Bibcode:2005PhT....58l..34H, doi:10.1063/1.2169442, retrieved 2015-03-08– via University of Notre Dame, Notre Dame, IN, author's personal webpage, From Schopenhauer he had learned to regard the independence of spatially separated systems as, virtually, a necessary a priori assumption ... Einstein regarded his separation principle, descended from Schopenhauer's principium individuationis, as virtually an axiom for any future fundamental physics. ... Schopenhauer stressed the essential structuring role of space and time in individuating physical systems and their evolving states. This view implies that difference of location suffices to make two systems different in the sense that each has its own real physical state, independent of the state of the other. For Schopenhauer, the mutual independence of spatially separated systems was a necessary a priori truth.
Bassani, Giuseppe-Franco. Società Italiana di Fisica (ed.). Ettore Majorana: Scientific Papers. Springer. pp.XL. ISBN3540480919. His interest in philosophy, which had always been great, increased and prompted him to reflect deeply on the works of various philosophers, in particular Schopenhauer.
B.F. McGuinness. Moritz Schlick. pp.336–337. Once again, one has to understand Schlick's world conception, which he took over from Schopenhauer's world as representation and as will. … "To will something" – and here Schlick is heavily influenced by Schopenhauer –
See the book-length study about oriental influences on the genesis of Schopenhauer's philosophy by Urs App: Schopenhauer's Compass. An Introduction to Schopenhauer's Philosophy and its Origins. Wil: UniversityMedia, 2014 (ISBN978-3-906000-03-9)