figured bass
A Baroque notation system where numbers below a bass line indicate the chords to be played.
In Depth
Figured bass was the standard method of notating harmony in the Baroque era (roughly 1600-1750). The composer wrote out only the bass line and placed numbers (figures) beneath it to indicate the intervals above the bass that should be sounded. A 6 meant a sixth above the bass, a 6/4 meant a sixth and fourth, and so on.
The continuo player — usually a harpsichordist or organist — had to interpret these figures in real time, improvising a full chordal accompaniment. This required extensive training in harmony, voice leading, and style. The system is still taught in music theory classes today as figured bass analysis, which provides a powerful framework for understanding harmonic movement.
C.P.E. Bach wrote a famous treatise on figured bass realisation that is still used as a textbook today, over 250 years after its publication.