AP® Music Theory · Unit 4 · Topic 4.2
Chord Spelling and Doubling
Four voices singing a three-note chord means one note must be sung twice. Which note gets doubled, and which notes must never be doubled, is decided by stability: double the root, avoid doubling tendency tones like the leading tone.
A triad has only three notes, but four-part writing needs four. So one note has to double, meaning two voices sing the same pitch class, usually an octave apart. The question is which note gets the extra voice. The safest choice is the root, because the root is the chord's most stable tone. It can be doubled in nearly any position without creating problems, since it doesn't pull strongly toward any other pitch.
Tendency tones are different. The leading tone wants to resolve up to tonic, and in V going to I, that pull is strong. If two voices both carry the leading tone, both are obligated to resolve up to the same tonic pitch, and you either get parallel octaves between those two voices or you break the resolution in one of them. Neither option is acceptable, so the leading tone is never doubled, even though it's a perfectly legal member of the chord. For a G major triad in root position, G-B-D, double the root: G in the bass, then G-B-D arranged above, with G appearing twice. In first inversion, B is in the bass, but you still avoid doubling B if it carries tendency-tone behavior in context; usually the root G or the fifth D doubles instead.
A six-four chord flips this logic: the bass note, which is the fifth of the chord, often gets doubled because the six-four is usually passing or cadential, and doubling the bass keeps the harmony stable while the upper voices move. This same stability logic carries into minor triads, where the third carries the music's modal color, and into cadences, where doubling choices shape how smoothly a phrase comes to rest.
Key terms
- Doubling
- Writing the same pitch class in two of the four voices, usually an octave apart, to fill out a triad in four parts.
- Tendency tone
- A chord tone, like the leading tone, that has a strong pull to resolve in one direction and so is avoided as a doubled note.
- Root position
- A chord arrangement with the root of the triad in the bass voice.
- Six-four chord
- A triad in second inversion, with the fifth of the chord in the bass, often doubled for stability.
- Modal color
- The quality a scale degree like the third gives a chord, distinguishing major from minor sound.
Watch it explained
- How it worksHow does the rule to double the root and never double a tendency tone settle the voicing?
- How it worksWalk me through voicing a G major triad in four parts in root position and in first inversion.
- Worked exampleFind what gets doubled in a six-four chord and why the bass takes the extra voice.
- Common mistakeWhy doesn't doubling the leading tone work even though the leading tone is just another note in the chord?
- Common mistakeWhy isn't doubling the third of a minor triad as safe as doubling the root?
Check yourself
End of topic.