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Galant and classical eras

LaRue, Bonds, Walsh, and Wilson write in the second edition of The New Grove Dictionary of Music and Musicians that "the symphony was cultivated with extraordinary intensity" in the 18th century. It played a role in many areas of public life, including church services, but a particularly strong area of support for symphonic performances was the aristocracy. In Vienna, perhaps the most important location in Europe for the composition of symphonies, "literally hundreds of noble families supported musical establishments, generally dividing their time between Vienna and their ancestral estate ". Since the normal size of the orchestra at the time was quite small, many of these courtly establishments were capable of performing symphonies. The young Joseph Haydn, taking up his first job as a music director in 1757 for the Morzin family, found that when the Morzin household was in Vienna, his own orchestra was only part of a lively and competitive musical scene, with multiple aristocrats sponsoring concerts with their own ensembles.

LaRue, Bonds, Walsh, and Wilson's article traces the gradual expansion of the symphonic orchestra through the 18th century. At first, symphonies were string symphonies, written in just four parts: first violin, second violin, viola, and bass (the bass line was taken by cello(s), double bass(es) playing the part an octave below, and perhaps also a bassoon). Occasionally the early symphonists even dispensed with the viola part, thus creating three-part symphonies. A basso continuo part including a bassoon together with a harpsichord or other chording instrument was also possible.

The first additions to this simple ensemble were a pair of horns, occasionally a pair of oboes, and then both horns and oboes together. Over the century, other instruments were added to the classical orchestra: flutes (sometimes replacing the oboes), separate parts for bassoons, clarinets, and trumpets and timpani. Works varied in their scoring concerning which of these additional instruments were to appear. The full-scale classical orchestra, deployed at the end of the century for the largest-scale symphonies, has the standard string ensemble mentioned above, pairs of winds (flutes, oboes, clarinets, bassoons), a pair of horns, and timpani. A keyboard continuo instrument (harpsichord or piano) remained an option.

The "Italian" style of symphony, often used as overture and entr'acte in opera houses, became a standard three-movement form: a fast movement, a slow movement, and another fast movement. Over the course of the 18th century it became the custom to write four-movement symphonies, along the lines described in the next paragraph. The three-movement symphony died out slowly; about half of Haydn 's first thirty symphonies are in three movements; and for the young Mozart, the three-movement symphony was the norm, perhaps under the influence of his friend Johann Christian Bach. An outstanding late example of the three-movement Classical symphony is Mozart's Prague Symphony, from 1786.

The four-movement form that emerged from this evolution was as follows:

Variations on this layout, like changing the order of the middle movements or adding a slow introduction to the first movement, were common. Haydn, Mozart and their contemporaries restricted their use of the four-movement form to orchestral or multi-instrument chamber music such as quartets, though since Beethoven solo sonatas are as often written in four as in three movements.

The composition of early symphonies was centred on Milan, Vienna, and Mannheim. The Milanese school centred around Giovanni Battista Sammartini and included Antonio Brioschi, Ferdinando Galimberti and Giovanni Battista Lampugnani. Early exponents of the form in Vienna included Georg Christoph Wagenseil, Wenzel Raimund Birck and Georg Matthias Monn, while later significant Viennese composers of symphonies included Johann Baptist Wanhal, Carl Ditters von Dittersdorf and Leopold Hofmann. The Mannheim school included Johann Stamitz.

The most important symphonists of the latter part of the 18th century are Haydn, who wrote at least 106 symphonies over the course of 36 years, and Mozart, with at least 47 symphonies in 24 years.