Encompassing a wide variety of post-Romantic styles composed through the year 2000, 20th century classical music includes late romantic, modern, high-modern, and postmodern styles of composition. Modernism (1890–1930) marked an era when many composers rejected certain values of the common practice period, such as traditional tonality, melody, instrumentation, and structure. The high-modern era saw the emergence of neo-classical and serial music. A few authorities have claimed high-modernism as the beginning of postmodern music from about 1930. Others have more or less equated postmodern music with the "contemporary music" composed from the late 20th century through to the early 21st century.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): When did modernism take place?
1890–1930