How Do You Write a Chord Without Writing the Notes? Number the Intervals
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Baroque composers wrote out only the bass line and put numbers under it, leaving the player to build the chords. The shorthand saved enormous labour and required real skill to read.
What the numbers mean
The written bass line carries figures beneath the notes, and each figure gives the interval above that bass note at which another note should be played, counted in the scale of the key. A six under a note means a note six steps above the bass, a four and a six together mean both, and no figure at all means the ordinary arrangement of a third and a fifth above. Accidentals raise or lower the indicated note. The player reads the bass, works out from the figures which notes belong in the chord, and then chooses how to arrange and voice them, which is where the skill lies.
Why composers wrote this way
The shorthand solved several practical problems at once:
- •Writing out full keyboard parts by hand was slow and expensive
- •One bass line served whatever instruments were available
- •It could be played on organ, harpsichord, lute or harp equally
- •The player adapted the texture to the room and the forces
- •Copying parts for a performance was far quicker
- •Improvisation within the harmony was expected rather than forbidden
What the player actually does
Reading the notation well is a performing skill rather than a decoding exercise, and it was taught systematically for two centuries. The performer must choose how many notes to play, how to space them, which to double and how to move smoothly from one chord to the next while avoiding the parallel motions that the style forbids. They must decide how much to fill in, playing sparsely under a delicate solo and fully under a chorus. They may add passing notes, imitate the soloist's phrases and ornament freely. Two competent players realising the same page produce noticeably different results, which is the point rather than a flaw.
Who played it
The part was performed by a group rather than by one instrument, and knowing the usual composition makes baroque scoring legible. A chordal instrument realised the harmony, most often a harpsichord or an organ, with lute, theorbo or harp used in some contexts and occasionally more than one at a time. A sustaining bass instrument doubled the written line, typically a cello, a bass viol or a bassoon, giving the bass a weight that a plucked or keyboard instrument alone lacks. The combination was chosen to suit the music and the room, with an organ usual in church and a harpsichord in the theatre, and the same piece could be performed with different forces.
Why it disappeared and came back
The practice faded in the later eighteenth century as composers began specifying textures precisely, wanting control over exactly what sounded rather than delegating it, and as the piano replaced the continuo instruments. Published editions from the nineteenth century supplied written-out realisations, frequently thick and romantic ones, which is how generations encountered the repertoire. The historically informed performance movement from the mid twentieth century restored the original practice, retraining players to realise from the figures, and the skill is now taught again in conservatoires. Modern chord symbols in jazz and popular music do essentially the same job by a different notation, naming the chord rather than the intervals.
The takeaway
Figures under a written bass line give the intervals above it, leaving the player to build, voice and arrange the chords, which saved enormous copying labour and let one part serve any available keyboard or plucked instrument. Realising it well requires choosing texture, spacing and movement in performance, so two players produce different results. Jazz chord symbols do the same job by naming chords instead.