basso continuo, also called continuo, thoroughbass, or figured bass, in music, a system of partially improvised accompaniment played on a bass line, usually on a keyboard instrument. The use of basso continuo was customary during the 17th and 18th centuries, when only the bass line was written out, or “thorough” (archaic spelling of “through”), giving considerable leeway to the keyboard player, usually an organist or harpsichordist, in the realization of the harmonic implications of the bass in relation to the treble part or parts. A low melody instrument, such as a viola da gamba, cello, or bassoon, usually served to reinforce the bass line, and the keyboard player received additional guidance in most instances from figures placed above the bass notes, a kind of musical shorthand indicating the intervallic constitution of the chords in question.
Basso continuo composition was a logical outgrowth of the monodic revolution (c. 1600), which declared the supremacy of the treble in opposition to the textural homogeneity of Renaissance polyphony. The harmonic substance of multivoiced music was now literally contracted into an instrumentalist’s two hands; the immediate repercussions for both sacred and secular music prompted Agostino Agazzari as early as 1607 to publish a manual of instructions, Del sonare sopra ’l basso (“On Playing upon the Thoroughbass”).