Modern classical music is music written in the 20th century and beyond. Although much of it draws heavily on earlier forms, modern composers also experimented with rejection of long-held ideas; notably, Arnold Schoenberg questioned the traditional notions of harmony with his twelve-tone system[?], and John Cage questioned the very definition of music with his use of chance and found sounds.
... (1836)
Psychologie oder Wissenschaft vom subjektiven Geist (1837; 3rd ed., 1863)
Kritische Erläuterungen des Hegelschen Systems (1840)
Vorlesungen über Schelling ...