Although we tend to think of the entire 18th Century as the 'age of enlightenment' we must remember that the great revolutions happened in the
last quarter of the century and first part of the next.  Baroque characteristics, which we begin to note by 1600, persisted at least through the death of J.S.Bach (1750) and Handel (1759), though certainly the contrapuntal complexities of Bach were considered old fashioned in his old age. Nevertheless, it was in the music of his sons, Wilhelm Friedmann Bach (1710-1784), Carl Philip Emmanuel Bach (1714-1788), Johann Christoph Bach (1732-1795), and Johann Christian (1735-1782) and their contemporaries, that we begin to see a move toward something different.  A pre-Classical style first appears in a large quantity of music written from about 1725 to 1760, and many art, architectural, and literary works of the same period show characteristics which, while derived from Baroque elements, are not based on the same aesthetic principles. This Rococo style
(meaning rock work, think Versailles)  featured extravagance of detail, delicacy of structure, elaborate attention to insignificant details, and the choice of some frivolous subject matter.  Baroque music, with its strict rules, its conventional affections (emotions), and its monumental forms, became one of the first victims of the new direction.  Rococo music was valued much for its ability to please and entertain. One graceful melody was preferred to the multitude of intertwined melodic strands of the Bach fugue. Homophonic texture became the dominant texture, and the Baroque principle of one mood per movement gave way to the practice of contrasting moods within a movement, and musical forms suited to this different content emerged. The musical amateur was reborn (having been very much en vogue in the Renaissance, all children of a certain family status studied keyboard, a string instrument or took vocal lessons.

The Sonata form (which is a harmonic context for melodic development), and the serenade (or divertimento) came into being, along with a new expressiveness in the melody, a new type of accompaniment, and the careful marking of dynamic changes in the music. (Sequence + crescendo = Mannheim Rocket etc.). These new devices were experimented with considerably, and in time passed on to the great Viennese masters we associate with the mature Classical period. First movement form was one of the most obvious changes. The Baroque practice of spinning material out of short melodic motives along with a fast harmonic rhythm gave way to longer melodic conceptions more akin to sentence structure supported by a much slower harmonic rhythm. Sequence became a device for reducing tension rather than increasing it as it had been in the Baroque era. (there are always exceptions). Musical phrases complete in themselves and with their own harmonic and cadential schemes were set opposite, or made to contrast with, other such phrases. The melodic material thus dominated the musical structure; there was little need for polyphonic treatment in the style, hence the use of counterpoint declined. Likewise, balanced pairs of phrases - often four measures in length - became typical. Cadences were spaced with a certain regularity, and sectional structures resulted.

WHAT DOES CLASSICISM MEAN?

COMPOSERS

The three Austro-Germanic composers Franz Josef Haydn (1732-1809), Wolfgang Amadeus Mozart (1756-1791) and Ludwig Van Beethoven (1770-1827) so dominate the 18th and early 19th century that there is little reason to mention other composers for purposes of this course.  Haydn is the trailblazer and the standard setter for the new style 'neo-classicism', Mozart, the flower of its' perfection, and Beethoven, the Promethean figure, who through his persuasive 'point of view', set instrumental music forever on a par with vocal music; and accomplishment never achieved before his time. Haydn is known for 104 symphonies and his many string quartets, Mozart for his operas, piano concertos, the quartets of his maturity and his 41 symphonies, and Beethoven for his monumental achievement in his 9 symphonies, his concertos and the 17 string quartets. 

All the forms that evolved in the Baroque era, particularly those of opera, concerto, sonata, oratorio and cantata continued to flourish in the the new style. Though the new style exhalted the single melody above the homophonic texture both Mozart and Beethoven, late in their careers began to show the knowledge and influence of the contrapuntal style of J.S.Bach, incorporating fugues and fugatos in many of their greatest works.

Among the new instrumental forms, Serenade, Divertimento, String Quartet, and Symphony, it is the Symphony that will become the most important multi-movement work culminating in the achievement of Beethoven. The Symphony is a four-movement 'Sonata' for orchestra in contrasting moods, keys and tempos, and it has been the most important instrumental genre from its' maturity in the late works of Haydn, Mozart and Beethoven through the 20th century.