Impressionists had already done this to an extent, beginning in the 1860's.

An iconic example of early twentieth-century modernism is Marcel Duchamp's Nude Descending a Staircase. Few people, if the title were lacking, would be able to recognize the described scene in the painting itself. The effect of such art is to deliberately disorient viewers and confront them with images that appear distortions of reality, or simply unreality.

There are numerous explanations or interpretations of this change in artistic technique. In purely technical terms, photography had made representational painting less "necessary." Artists began to seek new subjects beyond that which exists externally. In addition, from the Renaissance forward a huge body of artwork had been created, depicting the "real world" in every conceivable style and every aesthetic. By 1900 there was nowhere to go in terms of original expression unless the artist went beyond realism.

The deeper motivation for modernist art may have been the desire to show the "inner mind" on canvas. The psychoanalytic theories of Freud and others brought the unconscious into the forefront of man's view of himself. Abstract art is a kind of transcript of the unconscious, especially of the Freudian id, the repressed, hidden part of the psyche. By the early 1900's there was, as well, an increasing sense among intellectuals of the decline of the Western world. The arts could no longer confidently express the buoyant, positive worldview of the past in which man and his works are celebrated through literal portrayals. The disaster of World War I intensified this sense of hopelessness and decay, depicted in the jagged, distorted and "meaningless" expression made possible through abstract art.

In poetry T.S. Eliot's "The Love Song of J. Alfred Prufrock" is a seminal modernist work. Eliot's fragmented, often deliberately obscure verses are meant as a transcript of an insignificant man's negative and chaotic thoughts. Regular metrical and stanzaic forms are abandoned for a loose, constantly shifting structure. Imagery, such as the famous "patient etherised upon a table," which would have been traditionally considered unpoetic in the extreme, is used to jar the reader's sensibilities. Emotion, rather than being celebrated as in the past, is debunked and made to seem embarrassing. Eliot extended these elements in "The Waste-Land," in which a despairing tone is combined with parody and disjointed cultural and literary references, suggesting that the modern age consists of a post-historical wreckage rather than being a time of self-sufficiency and triumph, as the nineteenth-century had seen itself.

In music modernism took the form of the abandonment of the major-minor system on which music was built (and on which popular music still is today). Modern music was no longer necessarily written in a given tonality (or key). Igor Stravinsky and Charles Ives began writing bitonal music in which two different keys, such as C major and B major, were employed simultaneously. Modern composers used extreme dissonance as the norm rather than the exception it was in the past. Arnold Schönberg devised a system of "twelve tone" or "serial" composition in which tonality, as understood in the major-minor system, is abandoned entirely. The result of these modernist techniques is a musical equivalent of abstract painting.

In poetry, painting and music, art works were created in the twentieth century that broke radically with the past.