The idea
In the Baroque only the bass was written, with numbers above it: the keyboard player reconstructed the chords. The numbers indicate the intervals above the bass, not the degrees of the key. Today it is a central exercise in ABRSM programs (grades 6–8) and an excellent way to think of the bass as the engine of harmony.
The main figures
- No figure = 5/3: chord in root position.
- 6 = 6/3: first inversion.
- 6/4: second inversion.
- 7: seventh in root position; 6/5, 4/3, 4/2 (or 2): inversions of the seventh.
- 4–3, 7–6, 9–8: suspensions that resolve.
- An accidental alone (#, b, natural) refers to the third above the bass; a slashed 6 or 6# raises the sixth.
- A horizontal line after a figure means: hold the notes while the bass moves.
Examples in C major and A minor
- Bass C (no figure) = C. Bass E with 6 = C/E. Bass B with 6/5 = G7/B. Bass F with 4/2 = G7/F, which resolves to E 6 = C/E.
- Bass G with 4–3: G with a suspended C falling to B (Gsus4 → G).
- In A minor, bass E with # = E G# B: the sharp raises the third (G → G#).
How to realize it
- Respect the key signature and the figures.
- Normally double the bass in 5/3 chords, avoid doubling the leading tone.
- Voice leading: common tones held, stepwise motion, no parallel fifths or octaves.
Bridge to the present
Slash symbols (C/E, G7/F) are the modern equivalent: they indicate bass and chord, and the pianist realizes the voicing.
Real example
The ostinato bass of Pachelbel's Canon (in D: D A B F# G D G A) is a basso continuo: in C it becomes C G A E F C F G, realizable as C G Am Em F C F G. Dozens of pop songs derive from the same formula.