Basso continuo (also "thoroughbass," "figured bass," "basse cifrée" (Fr.), "generalbass" (Ger.) or "continuo") is the practice of creating (called "realizing" by specialists) an accompaniment from a composed bass part by playing the bass notes and improvising harmony above them. The term also refers to the composed part itself. Composers often wrote numbers ("figures," hence "figured bass") on the bass part to indicate the harmony, but the rules of continuo realization are firm enough that skilled players can play from an unfigured bass part. Continuo was standard practice in art music from roughly 1600 to the later 1700s.
Composers typically did not specify continuo instrumentation, but instruments commonly used included members of the lute family (the archlute and theorbo in particular), harp, guitar, instruments of the harpsichord and organ families, and even bowed-string instruments such as the lirone or viol. A common practice is to have several different instruments realize the continuo line (in the seventeenth century, theorbo and organ seems to have been a favorite combination; the published score of Monteverdi's Orfeo lists three theorbos, two harpsichords, two organs, regal and harp). The keyboard instruments offer facility, but not much dynamic variation. The other instruments offer dynamic expression, but less agility for fast-moving parts or complex harmonies.
In addition to the chordal instrument(s), melody instruments (cello, bassoon) can play the bass line, although this is not necessary and is less common in earlier music. The 1960s vintage notion that continuo consists of harpsichord and cello is derived from C.P.E. Bach's expressed preference for that combination in chamber music in about 1762, which may be of dubious value for music earlier than that. In orchestral music, the chordal instrument(s) play along with the bass section.
Since the art of continuo playing is not widespread except among early music specialists, modern editions of early music typically include a keyboard part that consists of the original continuo part plus an editor's realization of the harmonies for the right hand. Knowledgeable players avoid using these parts, to allow the realization to be more spontaneous. In addition, earlier continuo style tends to be more contrapuntally oriented than harmonically oriented, although this distinction can blur.
The origins of continuo cannot be pinpointed. Its predecessors could be said to include such things as songs with written-out lute accompaniment (which likely can trace their origins in turn to songs with improvised accompaniment) and organists assisting singers in liturgical performances. One common-sense notion is that any time an instrument capable of playing harmonies joins in an ensemble, the player will naturally fill in those harmonies. Another source of this practice is likely in intabulation, and the reduction of notation which it implies.
In liturgical music of the late 1500s the organist sometimes played from a "basso seguente" part which was a compiled sequence of whatever the lowest note in the composed parts was at a given point in the score. Intermedii and operas of the time included bass parts that were used by players of harmonic instruments, and it is in the earliest operas that the first figures appear. Emilio Cavalieri's Rappresentatione di Anima e di Corpo of 1600 and Ludovico Viadana's Cento Concerti Ecclesiastici of 1602 both contain prefaces that explain how continuo works and how to read the parts, making it clear that the practice was not widely familiar to performers at that time.
Some added remarks by Todd McComb, Alison Kranias, Philip Bayles.
To Early Music FAQHoward Posner