Which Note to Double in Each Chord — and Why It Matters

In four-voice writing (SATB), we always have one extra note. A triad has three notes; we have four voices. Which one gets doubled? The answer is not arbitrary.

The Hierarchy Within the Chord

Within any triad, the notes carry different hierarchical weight:

1. Root — defines the chord. It's the "safest" note to double.
2. Fifth — stabilizes the chord. It can be doubled without problem in most contexts.
3. Third — defines the mode (major/minor). Doubling it is problematic because it concentrates too much weight on the note that defines the chord's color.

This hierarchy directly explains the doubling rules.

Root Position (chord in 5th position)

When the bass carries the root:

• Double the root — always correct
• Double the fifth — generally correct
• Avoid doubling the third — especially in dominant chords (V), where the third is the leading tone that has an obligatory resolution toward the tonic

C major — root position
Soprano: E (3rd)
Alto:    G (5th)
Tenor:   C (root)
Bass:    C (doubled root) ✓

First Inversion (chord in 6th position)

With the third in the bass, the situation changes:

• Double the soprano — the highest voice gives the melodic color
• Double the root or fifth — perfectly valid
• Avoid doubling the bass — doubling the third (which is already in the bass) overloads that note

First inversion is more unstable than root position, and that instability is functional: it's used to create movement and variety of color.

Second Inversion (⁶₄ chord)

Second inversion is the most special case. With the fifth in the bass, the chord sounds particularly tense and unstable.

Golden rule: always double the bass (the fifth).

C major — second inversion (⁶₄)
Soprano: C (root)
Alto:    E (3rd)
Tenor:   G (5th)
Bass:    G (doubled 5th) ✓

This doubling reinforces the bass and prepares the resolution that almost always follows a ⁶₄ chord. The most common use of the ⁶₄ chord is the cadential ⁶₄ — I⁶₄–V–I — which appears in virtually all tonal music of the common practice period.

The Special Case of the Leading Tone

In the dominant chord (V), the third is the leading tone — a half step below the tonic. This note has a very strong acoustic tendency toward resolution. If you double it, you need to resolve both instances toward the tonic, which creates unavoidable parallel fifths or octaves.

So: never double the leading tone. Not in V, not in VII°.

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How the Virtual Teacher Practices This

In the Harmony Course, every MIDI exercise you submit to the Virtual Teacher is analyzed note by note. If you double the leading tone in a dominant chord, you'll receive specific feedback indicating exactly which beat of the measure it occurred on and which voices are involved.

This immediate feedback — the equivalent of having a teacher review every note — is what distinguishes active practice from simply reading theory.