Definition
In the given bass exercise you receive only the bass line, without figures, and you must choose the chords and write the three upper voices. It is the opposite exercise from harmonizing a soprano and teaches you to “hear” functions starting from the bass, as a keyboardist does when playing from a bass line or a producer who starts from a bass line.
What the bass tells you
Every note of the bass can be the root, the third (chord in first inversion), or the fifth (second inversion, only in specific cases) of a chord. Some clues:
- Leaps of a fourth or fifth: almost always root-position chords.
- Motion by step: suggests inversions that make the line singable.
- Leading tone in the bass (B in C): V6 or vii°6, which resolve to the tonic.
- Fourth degree falling to the third (F → E): V4/2 → I6, or ii6 or IV.
- Fourth degree rising to the fifth (F → G): IV or ii6 → V.
- Sixth degree (A): vi or IV6.
- Second degree between I and III (D between C and E): vii°6, V4/3, or a passing V6/4.
- Repeated or held notes at the end of a phrase: often a cadential six-four followed by V.
Step-by-step method
- Identify the key and any modulations (recurring accidentals in the bass).
- Mark the cadences at the ends of phrases: there the chords are almost obligatory (ii6–V–I, IV–V–I, I6/4–V–I).
- For each note choose a possible chord and check that the succession respects the functions (tonic, predominant, dominant).
- Write the soprano first, as a counterpoint to the bass: prefer contrary motion, intervals of thirds, sixths, and tenths, and a melody with a climactic point.
- Fill in alto and tenor with the missing notes, respecting doublings and the rules of motion.
- Recheck parallel fifths and octaves, especially between the outer voices.
Example in C major
| Bass | C | D | E | F | G | A | F | G | C |
|---|---|---|---|---|---|---|---|---|---|
| Chord | I | V4/3 | I6 | ii6 | V | vi | IV | V | I |
| Soprano | E | F | G | D | B | C | A | B | C |
Notes on the model: between V4/3 and I6 the seventh (F) rises to G because the bass rises by step in parallel tenths, a permitted exception; ii6–V and V–vi move the outer voices in contrary motion; in the final IV–V–I cadence the leading tone rises to the tonic in the soprano.
Practical rules
- Never use the second inversion “by chance”: only cadential, passing, or neighbor.
- Avoid two identical consecutive inversions on the same function without a reason.
- Vary the harmonic rhythm: change chords more often toward the cadence.
- If two choices are equivalent, prefer the one that gives the soprano a more beautiful line.
Common mistakes
- Treating every bass note as a root: the line becomes rigid and full of leaps in the upper voices.
- Forgetting the cadences and harmonizing note by note.
- Writing the soprano last: you get broken melodies and parallels with the bass.
Examples from the repertoire
- The Neapolitan partimenti of the 18th century were given basses to be realized at the harpsichord: the same skill, taught to composers such as Pergolesi and Cimarosa.
- The descending bass lines of pop (C–B–A–G, like the one in Procol Harum's “A Whiter Shade of Pale”) can be treated as a given bass: I – V6 (or iii6) – vi – I6/4 (or vi7).
How to use it in composition
- Start from an interesting bass line and derive the chords: you get progressions with natural inversions and smoother voice leading.
- In songwriting, the bass moving by step under held chords (slash chords) comes precisely from this technique.
Exercise
- Harmonize the bass G–A–B–C–D–B–C–D–G in G major, writing the soprano first.
- Harmonize the same bass in two different ways and compare the soprano melodies.
- Take the bass line of a song you love and reconstruct the chords with Roman numerals.
Connections
Figured bass; Rule of the octave; Partimento and the Neapolitan school; Harmonizing a melody; Counterpoint of the outer voices; Slash chords and inversions in pop.