The trombone (Italian, “big trumpet”) is well known as a band instrument (e.g., 76 of them in The Music Man) or part of a jazz combo (Jack Teagarden and friends), and, since Wagner, as a regular member of the symphony orchestra, normally in groups of three. Before Wagner trombones were only occasionally used in symphonies, appearing suddenly and spectacularly (alto, tenor and bass) in the finale of Beethoven’s Fifth. Prior to that splendid moment, trombones were used as choral doublers (including in several Bach cantatas and regularly in contrapuntal sections of the Viennese classical Mass), or less often, as a coloristic group in opera — think of the graveyard scene in Don Giovanni or even all the way back to Monteverdi’s Orfeo, when the trombones were sackbuts. Beethoven, apart from one or two instances, seems to have been reluctant to use the trombone as a solo instrument, or in a non-doubling choir of three; by the time of the Fifth Symphony (1808), he was already quite deaf, and may have only guessed at the trombone’s coloristic utility, although one day in 1812 he did write three Equale for a quartet of trombones (WoO 30).
It was Franz Schubert, 27 years younger than Beethoven, who really liberated the trombone in the symphony orchestra. Schubert had much experience with orchestras ever since he was a child, and began incorporating trombones into his symphonic scores as early as 1821. In 1825 he composed his largest and greatest symphony, the one in C major that we now officially call No. 8, the “Great,” after variously numbering it 7, 9 or even 10. The first movement has this golden melodic moment, one of many:
Walter Piston’s Orchestration, IMNAAHO the finest of all textbooks on this subject, writes of this passage: “The pianissimo unison of three trombones….makes a full, round tone, without being loud.”
In the second movement, Andante con moto, Schubert keeps the trombones occupied with great flexibility. A single trombone provides a smooth melodic bass for eight woodwinds; the three trombones reinforce the tutti regularly in ff ; and the group independently dialogues with woodwinds and strings:
This brief but sweet handoff at the end of the B section is also a foretaste of the future, showing what most later classicists of the orchestra liked to do with three or four horns that they couldn’t manage with valveless instruments in 1825. What Schubert does with it only a few minutes later, at the end of the B’ section in A major, is a miracle of orchestral sound; see mm. 321-330, with pizzicato strings, plus clarinets (Schubert does add one horn to the trombones, so he can have a complete V9).
In the finale, just before the Recap, the trombones are again pp but with menacing prescience:
The trombones here are a signpost to the beginning of the Recap in the wrong key, E-flat major, which of course is only part of the story.