As this technique grew, publishers began publishing thoroughbass reductions of large-ensemble pieces to support smaller groups of musicians. In these publications, figures (numbers above or below the bass line) were included—sometimes only for difficult or non-standard chords, and eventually for most chords, enabling more amateur musicians, as well as students, to make use of the technique. These bass lines with figures became known as “figured bass” lines.
J.S. Bach, Flute Sonata in C Major, ii., BWV 1033. The upper part is played by the flute, the lower part is the basso continuo line, played by a keyboardist who uses the numbers below the staff (figures) to guide the chords played above this bass line.
To this day, harpsichordists performing in Baroque ensembles will often put their left hand to the same “bass” line that the cellos play, and will improvise right-hand chords (with contrapuntally sound embellishment) according to the figures provided with the bass line.
Though most music students are not Baroque keyboard specialists in training, thoroughbass, or basso continuo, can be a valuable tool in the study of harmony and voice-leading. In the study of harmony, a thoroughbass line can play a valuable role as a harmonic reduction of a complex texture, in order to example and understand better the harmonic skeleton underlying a passage. In aural dictation, transcription, and analysis, the bass line and the melody are often the most prominent (and most important) lines in a passage, and knowing how the inner voices tend to relate to the bass line and melody can aid in a number of listening and aural-analysis tasks. In voice-leading, the basso continuo texture affords a straightforward environment in which to make a gradual, staged progression through the intricacies of writing musical lines in a harmonic texture—and to do so without paying significant attention to harmony.