Beginning around 1720 new developments once again began to undermine the prevailing musical style. Younger musicians found baroque counterpoint too rigid and intellectual; they preferred a more spontaneous musical expression. In addition, the late baroque ideal of establishing a single emotional quality and maintaining it throughout a composition seemed constricting to these younger composers.
The reaction against baroque style took different forms in France, Germany, and Italy. In France the new current, often called rococo or style galant (French, "courtly style"), was represented by the French composer François Couperin. This style emphasized homophonic texture, that is, melody with chordal accompaniment. The melody was ornamented with embellishments such as short trills. Instead of an uninterrupted stream of music, as in a baroque fugue, French composers wrote pieces consisting of combinations of separate phrases, as in music for dance. The typical composition was short and programmatic, that is, it portrayed nonmusical images such as birds or windmills. The harpsichord was the most popular instrument, and many suites were written for it.
In northern Germany the preclassical style was called empfindsamer Stil (German, "sensitive style"). It encompassed a wider range of contrasting emotions than the style galant, which tended to be merely elegant or pleasant. German composers usually wrote longer compositions than the French and used a variety of purely musical techniques to unify their pieces. They did not rely on nonmusical images, as did the French. The Germans thus played a significant role in the development of abstract forms, such as sonata form, and in the development of large instrumental genres, such as concerto, sonata, and symphony.
In Italy the preclassical style did not have a special name, perhaps because it did not break sharply with music of the immediate past. Italian composers, however, contributed a great deal to the development of new genres, especially to the symphony. The Italian opera overture, often called a sinfonia, usually had no musical or dramatic connection with the opera it introduced. Italian musicians sometimes played opera overtures in concerts, and composers eventually began to write independent instrumental pieces following the format of the overture. This format consisted of three movements, the first and last in fast tempos, and the middle one in a slow tempo. Within each movement the progression of musical ideas usually followed a pattern that eventually evolved into sonata form.
Once Italian composers had established the idea of writing an independent instrumental sinfonia, the Germans took over the idea and applied much intellectual ingenuity to it. The principal German centers of activity were at Berlin, Mannheim, and Vienna. Largely as a result of German activities, differentiated musical forms, genres, and media arose. A distinction was made between the medium of chamber music, in which one instrument plays each part, and the medium of symphonic music, in which several instruments play each part. Within the category of chamber music, composers began to distinguish among several media, such as the string quartet, the string trio, and the keyboard sonata with violin obbligato. For the orchestral medium, composers wrote not only symphonies but also concertos for solo instrument and orchestra.
The symphony, sonata, concerto, and string quartet all followed similar formal outlines. They were in three or four movements, one or more of which was in sonata form. Made possible by the sophisticated use of tonality that had developed by the end of the baroque era, sonata form arose in the mid-18th century and exploited the complex web of harmonic relationships among separate tones and chords within a key, and among different keys. Sonata form was based on a movement away from and back to a principal key. To this was added the statement of opposing themes at the outset of a movement and the elaboration or separate development of one or all later on.
The climax of 18th-century musical development came at the end of the century in the music of a group of composers known as the Viennese classical school. The most important of these composers were Joseph Haydn, Wolfgang Amadeus Mozart, and Ludwig van Beethoven.
Opera in the 18th century also underwent many changes. In Italy, where it was born, opera had lost much of its original character as a drama with music. Instead it had become a series of arias designed to display the talents of singers. Several European composers reintroduced instrumental interludes and accompaniments as an important element. They made greater use of choral singing and introduced greater variety into the forms and styles of the arias. They also tried to combine groups of recitatives, arias, duets, choruses, and instrumental sections into unified scenes. The most important reformer was the Bavarian-born Christoph Willibald Gluck, whose most influential operas were written in Vienna and Paris from 1764 to 1779. Opera in the classical period climaxed in the stage works of Mozart, in which every aspect of the vocal and instrumental lines contribute to the plot development and characterization.