To start with, the terms modernist and modernism require a word of explanation. They mean something different from modern or contemporary, terms that refer to anything at all that happens to take place in the present; the -ist and -ism at the end of the word modern give them an extra twist. The terms refer to a special self-consciousness, on the part of the artists themselves, of their position at the forefront of new developments. The modernists of 1900 were artists and intellectuals who insisted on a particular vision of modernity: anti-traditionalism. They formed a specific movement marked by radical experimentation, which first peaked in the years 1890 through 1920 — a period of breakthrough works by such figures as novelists Marcel Proust and James Joyce, poets Ezra Pound and T. S. Eliot, and painters Pablo Picasso and Henri Matisse.

The chief composers associated with the modernist movement in this early phase were Claude Debussy, Arnold Schoenberg, and Igor Stravinsky. They are often referred to as members of the musical “avant-garde.” Avant-garde — meaning “vanguard” — was originally a military term, but it has long been embraced by radical artists and thinkers to denote the forefront of their activity. Later, about 1950, a second phase of avant-garde modernism set in, involving a new generation of composers.

Not all modernist composers were members of this avant-garde. The full variety of modernist music includes not only radical experimentation but also more modest kinds. It embraces late nationalist composers, striving to incorporate their nations’ musical idioms in new ways. It also includes many composers who incorporated into their works the newly prominent gestures of popular music, as well as some who resisted the styles of the avant-garde, preferring to continue developing the spirit of late Romanticism. All these composers, alongside more radical innovators, showed the special self-consciousness of their place in music history that defines modernism.

Through the twentieth century, these many styles mixed, merged, and interacted with one another to form the colorful tapestry of modernist classical music. At certain times assertive avant-garde experiment seemed to gain the upper hand — for example, from 1900 to 1920 and from 1950 to 1970 — while other times were periods of consolidation, for example in the 1920s and 1930s.