Trio Sonata

The trio sonata is a Baroque chamber form for two equal melody instruments (typically two violins, though flutes, oboes and recorders all appear) plus basso continuo (cello or bass viol playing the bass line, with harpsichord, organ or theorbo realizing the figured-bass harmonies). Despite the name, four players are usually required; 'trio' refers to the three written voices, not the number of musicians. The form divides into two stylistic types: the sonata da chiesa ('church sonata,' typically four contrasting movements in slow-fast-slow-fast order), and the sonata da camera ('chamber sonata,' a suite of stylized dances).

The form was codified by Arcangelo Corelli (1653-1713) in his published collections of trio sonatas — Op. 1 (church, 1681), Op. 2 (chamber, 1685), Op. 3 (church, 1689) and Op. 4 (chamber, 1694). Corelli's models circulated across Europe and shaped subsequent generations. Henry Purcell, Francois Couperin, Telemann, Handel and J.S. Bach all wrote trio sonatas; Bach's contributions include the trio sonata in 'The Musical Offering' BWV 1079 (1747) and a series of organ trio sonatas (BWV 525-530) where the player produces all three lines with two hands and pedal. The form declined in the late 18th century as the string quartet and accompanied sonata replaced it.

Listen to how the two upper voices imitate each other — one violin states a phrase and the second enters a beat or two later with the same line, creating canonic tension that resolves at structural points. The bass line is rarely just supporting; in good writing it has its own melodic life. Continuo realization is partly improvised; different harpsichordists fill in different chord voicings from the same figured-bass shorthand.

Corelli's Op. 3 No. 1 (church sonata in F major, 1689) is the canonical entry — clean structure, melodic clarity, the model for the rest of the Baroque. Then jump to Bach's trio sonata in 'The Musical Offering' (1747) to hear what the form became in its most refined version.

Corelli published only six collections in his lifetime — four sets of trio sonatas, one set of solo violin sonatas, and the concerti grossi Op. 6 — but their influence across Europe was outsized; later composers studied them as models of how to write tonal music in the new style.