(It., from tre, formed in imitation of duo).
(1) A piece of music for three players. The commonest types are the Piano trio (piano, violin, cello) and the String trio (violin, viola, cello); see also Chamber music, Trio sonata and (for vocal music) Terzet.
(2) In the 18th century, the term ‘trio’ was applied to an instrumental piece for three obbligato voices, without further accompaniment, in strict style. Many such pieces belong to the realm of academic music, being used by theorists to demonstrate rules of counterpoint and composition. There are, however, trios of this kind in the keyboard music of J.S. Bach, notably in his organ sonatas and his sinfonias (or three-part inventions), where all three voices are equally important and all three are continuously engaged in working out the musical ideas. The canons of the Goldberg Variations, except that at the 9th, are trios. Trios are also prominent in his organ chorales, where the variety in treating various combinations of voices is striking.
Related to the strict trio is the permutation fugue, cultivated in 17th- and 18th-century Germany by such composers as J.A. Reincken and J.S. Bach. In this technique neither episodes nor harmonic digression are allowed, but rather a subject and two countersubjects are presented continuously, as the voices exchange material. Reincken's Trio Sonata in A minor (1697) has as its second movement a textbook example of a permutation fugue; the sonata was transcribed by Bach as the keyboard sonata bwv965.
(3) From the 17th century onwards, the second of two alternating dances was called a ‘trio’ whether or not it is actually scored for three voices; a typical form is minuet–trio–minuet da capo. The trio of this kind is a common feature of 17th- and 18th-century music for dancing; its main purpose is to provide enough music for the figures of an entire dance (for an ordinary minuet may require more than 120 bars of music). The alternation of two dances provides opportunity for variety in texture and sonority. Lully alternated two minuets in the Prologue to Armide; the first, in his normal five-part string scoring, is followed by a trio for two oboes and bassoon. In the prologue to Persée, a passepied en trio is played (two oboes and bassoon) and sung (two sopranos and continuo) in alternation a total of five times to provide enough music for the dancers.
An analogous use of the term is Georg Muffat's, in Ausserlesene Instrumental-Music (Passau, 1701; Eng. trans. in StrunkSR1), a set of 12 concerti grossi, where ‘trio’ signifies ‘concertino’ or ‘petit choeur’. The ripieno is for five-part string orchestra and the trio or concertino is for two oboes and bassoon or strings. There are many dance movements in Muffat’s concertos, but the trio scoring is used not for long-range contrast (as in the dance suite) but for dynamic contrast within a single dance: he often started a dance movement with the wind trio playing alone; the repeat is then written out with much fuller scoring. Muffat said in his foreword that in the sudden contrast ‘of loud and soft, the ear is ravished by a singular astonishment’.
The
suites of J.S. Bach contain many bourrées, gavottes, minuets and passepieds
alternating with trios which, although as likely to be in two or four voices as
in three, are still labelled ‘trio’. There are also many independent dances in
three voices: an example is the sarabande en trio in his Suite in E
bwv819.
Two or even more different dances may be used in alternation: the minuet of
Bach's Brandenburg Concerto no.1 alternates with a trio (oboes and bassoon), a
polacca or polonaise in 3/8 (strings) and a second trio in 2/4 (two horns and
unison oboes). The bourrée from the Prologue to Achille et Polixène by
Lully and Collasse alternates with a minuet; and Mozart wrote a pair of minuets
with alternating contredanses (k463/488c).
Most
trios of the 17th and early 18th centuries are in the same key as the movements
to which they belong, though they often involve a contrast between major and
minor modes. During the Classical period composers often cast trio sections in
remoter keys, particularly Haydn (for example the trios in E and D, to movements in G and F respectively in
the op.77 string quartets) and Beethoven (Symphony no.7, trio in D to a
movement in F). Trios of this period are usually lightly scored: in the trios
of his late symphonies Haydn often wrote a woodwind melody with a simple
accompaniment, and in several Beethoven symphonies (e.g. nos.1, 3, 4, 8 and 9)
the trio is given a distinctive character by the prominent use of wind
instruments and lighter textures. Mozart (Serenade k361/370a,
Symphony no.36) and particularly Schubert (Symphony no.5) often gave their
trios a ländler-like character. Several composers, including Mozart (Serenade k361/370a, Clarinet Quintet) and Schumann (Symphonies
nos.1 and 2) used two different trios, providing more extended movements in the
form ABACA; Beethoven (Symphonies nos.4 and 7) has a single trio recur,
as does Schumann (Symphony no.4), in the form ABABA. Several composers
from the time of Beethoven (Symphonies nos.6 and 9) onwards used contrasting
metres in their trio sections. The term ‘trio’ was still used in symphonic
works by Brahms, Tchaikovsky, Bruckner and Mahler, and the concept of a
contrasting or lightly scored middle section to a scherzo-type movement, even
without the term, persisted well into the 20th century.
H.C. Koch: Musikalisches Lexikon (Frankfurt, 1802/R)
J. Eppelsheim: Das Orchester in den Werken Jean-Baptiste Lullys (Tutzing, 1961)
H.M. Ellis: The Dances of J.B. Lully (1632–1687) (diss., Stanford U., 1967)
C. Wolff: ‘Johann Adam Reincken und Johann Sebastian Bach: zum Kontext des Bachschen Frühwerks’, BJb 1985, 99–118; Eng. trans., enlarged, as ‘Johann Adam Reincken and Johann Sebastian Bach: on the Context of Bach's Early Works’, J.S. Bach as Organist, ed. G. Stauffer and E. May (London, 1986), 57–80, repr. in Bach: Essays on his Life and Music (Cambridge, MA, 1991), 56–71
M. Marissen: ‘Concerto Styles and Significations in Bach's First Brandenburg Concerto’, Bach Perspectives, i (1995), 79–101
ERICH SCHWANDT