Open a printed score from the Baroque era — Bach, Handel, Vivaldi, roughly 1600 to 1750 — and the bass part often looks strangely incomplete: a single melodic line, with a scattering of numbers written beneath the notes. That's not an unfinished piece. It's basso continuo, a standard Baroque practice that deliberately left the exact harmony only partly written down, trusting a keyboard or lute player to improvise the rest live, differently, in every single performance.
Figured bass: a shorthand, not a full script
The numbers under the bass line, called figured bass, indicated which chord to build above each bass note — but not the specific voicing, rhythm, or ornamentation of how to actually play it. A continuo player, typically at a harpsichord or organ, read the bass line and its figures and improvised a full harmonic accompaniment on the spot, filling out the chords, adding passing notes and embellishments, and responding in real time to the other musicians. A cello, bassoon, or theorbo often doubled or reinforced the bass line itself, while the keyboard or plucked-string player supplied the harmony above it — together forming the "continuo" group, the harmonic backbone that ran underneath nearly the entire ensemble.
Why composers trusted performers with an unfinished part
This wasn't composers being lazy or leaving work unfinished — it reflected genuine, expected musicianship at the time. A trained Baroque keyboardist was expected to be able to realise figured bass fluently, the way a modern jazz pianist is expected to read chord symbols and improvise an appropriate voicing rather than needing every note written out. This gave Baroque performance a genuinely improvisational, variable character that's easy to miss when the music is heard today from a fixed, fully notated modern edition — the same piece, performed by two different continuo players on two different nights, could sound noticeably different in its harmonic filling, even though the underlying bass line and figures were identical both times.
What we're still unsure about
The mechanics of figured bass notation and its standard conventions are well documented in surviving treatises from the period, so the basic system isn't in dispute. What's genuinely harder to recover is exactly how a specific historical performance actually sounded — since improvised realisations were, by definition, never fully written down, modern historically informed performers reconstructing "authentic" Baroque practice have to make interpretive judgment calls based on surviving treatises, contemporary accounts, and stylistic conventions, without ever having a truly definitive record of precisely what any single historical keyboardist actually played on any given night.
This sits inside Baroque Music (Bach, Handel, Vivaldi), one of seven topics in Music History, one of four domains in Music, one of seventeen subjects the app can quiz you on.