What is the origin of the western symphony?

Answer 1

The term "sinfonia" was originally used as a sort of synonym for an Overture or a ricercar during the Baroque Era. (Antonio Salieri actually still used it that way well into the Classical Era) It gradually became customary to compose sinfonias in 3 movements, fast-slow-fast, similar to a concerto without a soloist. Franz Josef Haydn, known as the Father of the Symphony, popularized the most commonly recognized 4 movement format by adding a scherzo with trio movement after the slow movement. This format is by no means a rule, however. Many composers, especially in the Romantic Era, expanded and altered the symphony. Beethoven's 6th, for instance, is in 5 movements and his 9th introduced the concept of a "Choral" symphony.