As the world made the transition from 19th-century Romanticism to 20th century Modernism, its inhabitants witnessed a musical change that would forever affect the course of history. Rejecting the emotions-dominated Romantic period, the 20th century wanted to represent the world as it was actually perceived. Artists desired to be objective, while objects existed on their own terms. While past eras concentrated on spirituality, this new period placed emphasis on physicality and things that were concrete. A focus on restraint and balance resulted in the Neoclassicism of the 1920s, and modern artists sought a return to primitive life in their work in a movement called Primitivism. Neoclassicism rejected the programmatic music characteristic of the 19th-century era. Instead, composers looked back to the 18th-century Classical period’s absolute music of order and clarity in a "back to Bach" movement of the early 1920s (Machlis & Forney 460).

Returning to a classical style affected composers in different ways, and especially had an impact on Russian-born composer, conductor, and pianist Igor Stravinsky (1882-1971), who wrote that "the more art is controlled, limited, worked over, the more it is free" (qtd. in Machlis 161). Through bringing back absolute forms, such as the symphony, chamber music, the sonata and concerto, earlier musical forms were also revived: suite, divertimento, toccata, and fugue (Machlis 163). Nationalism was important to Romanticism, but composers in the 20th century wanted to retain the original sound of the folk singers. With more options in technology available to them, composers like the Hungarian masters Béla Bartók (1881-1945) and Zoltán Kodály (1882-1967) could travel among the peasant villages and record the music making. In fact, Bartók spoke of those days among the peasants as the happiest of his life.

Stylistic musical changes were being made in many European countries, in nonwestern countries, and in America. Paris was the center for music, art, and literature during the early years of this period, and Impressionism was a particular style that evolved out of this city during the second half of the 19th century. Composers imitated the painters’ impressionist subtle style, which French composer Claude Debussy (1862-1918) thought to be "discreet" (qtd. in Machlis 86). But music professors of Debussy at the Paris Conservatoire warned: "Beware of this vague impressionism which is one of the most dangerous enemies of artistic truth" (qtd. 86). Ironically, Debussy and other impressionist composers hated this label, and he complained of "what some idiots call impressionism, a term that is altogether misused, especially by the critics" (qtd. 86). Another French modern movement is called musique concrčte, a late 20th-century style in which composers derive musical sounds from nature, everyday sounds, and general noise, altering them to fit their piece. Modern French composer, organist, and teacher Olivier Messiaen (1908-1992) also felt inspired by nature, notating songs of French birds in pieces that reflected an intense love for mysticism.

The 1920s rejection of Romanticism was also found in works of French author Jean Cocteau, who joined a contemporary French composer named Erik Satie (1866-1925) to mentor a group of young Paris musicians called Les Six. With a focus on objectivity and understatement in their compositions, three of these men later became musical leaders in France: Francis Poulenc (1899-1963), Darius Milhaud (1892-1974), and Swiss composer Arthur Honegger (1892-1955). Spreading throughout Europe after 1918, a movement called Dadaism began in Switzerland. Comprised of artists and writers who produced works based on simple concepts, this movement rejected the idea and accepted concept of Art, as well as any form of art that was complex. Influencing Les Six, the Dadaists fused with Surrealists, a group that focused on the dream world. Promoting simplicity, Dadaist Erik Satie and others took music on a different track after World War I and introduced "everyday" music, or "workaday music" that interested the average listener and producers (Machlis 159). Besides Satie, German-born American Paul Hindemith (1895-1963), Austrian Ernst Krenek (1900-1991), and German composers Kurt Weill (1900-1950) and Hanns Eisler (1898-1962) were involved. Hindemith remarked in 1927 that "a composer should write today only if he knows for what purpose he is writing" (qtd. 160).

Expressionism was the German version of Impressionism, an idea that came from painting and was musically prominent in central Europe and with Viennese composers. Influencing Austrian composer, conductor, and teacher Arnold Schoenberg (1874-1951), Expressionism featured melodic leaps and instruments that played in their very high and low registers.

Since they no longer depended solely on patrons for financial support, composers grew apart from the public they had been close to in earlier periods. Some revived the 17th- and 18th-century French court music that was meant strictly for entertainment (Machlis 156-7) whereas others used satire, irony, and humor marked by dissonance. Jazz music became important after the first World War, especially in America. Using syncopation and polyrhythm, the melody of a jazz group was represented with the reeds and brass instruments, while rhythm was found in percussion, string, and piano instrument families.

Considered a Jazz Age, the 1920s in America featured George Gershwin’s Rhapsody in Blue, An American in Paris, and Piano Concerto in F (Machlis 352), as well as Leonard Bernstein's musical theater with jazz influences. Some musical selections were inspired by urban life, specifically with the rhythmic hum of the city. Opera subjects exploited city life, seen in Hindemith’s News of the Day from 1929 (Machlis 154-5).

Moving from the Romantic period and into the 20th century and throughout this modern era, instruments changed and developed drastically. For example, pianists will sometimes reach inside the piano to pluck the strings while performing; vocalists may whisper or laugh, and even hiss. More than any other family, percussion instruments expanded. But orchestras in the 20th century dwindled in size. As orchestral music became more concise and complex, the length of compositions also diminished. Symphony orchestras expanded in other ways, as their goal was to make individual instruments stand out and be heard.

Expanding instruments in notes, technique, and other areas, performers had greater possibilities to work with. Mixed chamber ensembles with three to 20 players featured piano, strings, winds, and percussion. With advances made in the percussion family, musicians took an interest in African, Asian, and Latin American music. American pianist and composer John Cage (1912-1992) introduced the "prepared piano" of the 1940s that highlighted a small percussion orchestra connected to the keyboard (Machlis 460). Singers also created percussive effects vocally through humming, hissing, and other rhythmic expressions. Gradually the percussive sound began to dominate the orchestra, and pianos became part of the ensemble, as opposed to the virtuoso solo instrument it had been during the Romantic period.

Was melody a primary emphasis of 20th-century compositions? American composer Aaron Copland (1900-1990) once said that "the melody is generally what the piece is about" (qtd. in Machlis 11). But the concept of melody changed with the modern time, resulting in no standard patterns that musicians were used to. As melodic themes were generally stated only once in a work, music required focused attention of listeners to figure it out. Some modern music has no melody, and many feature tiny clusters of melodic ideas and themes throughout a piece. Melodies had wide leaps of notes and were often dissonant, with the 20th century turning back to past eras of counterpoint. Other older forms were a place to explore this dissonance in separate lines so each part could be easily heard.