What is the cadential six-four, and why does it behave like a delayed dominant?
Topic 5.6 Cadential 6/4 Chords: use the cadential six-four (I6/4 to V) and part-write its suspension-like resolution of the sixth and fourth above the bass.
A focused answer to AP Music Theory Topic 5.6, covering the cadential six-four chord (I6/4 over the dominant bass), why it behaves like a decorated dominant, the resolution of the sixth to the fifth and the fourth to the third above the bass, doubling the bass, and metrical placement, with a worked resolution.
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What this topic is asking
The College Board (Topic 5.6) wants you to use the cadential six-four chord (written I6/4 over the dominant bass, sometimes labelled V6/4 to 5/3) and to part-write its suspension-like resolution, where the sixth and fourth above the bass fall by step to the fifth and third of the dominant.
A decorated dominant
This is why many analysts label it V6/4 to 5/3, showing that the bass is the dominant throughout while the upper notes shift from 6 and 4 down to 5 and 3.
The suspension-like resolution
The two falling resolutions create the characteristic leaning, then releasing, sound of a cadential six-four. Getting the metric placement right (strong beat, then resolution) is part of writing it idiomatically.
Why it is a dominant, not a tonic
The central idea is that function comes from context and bass, not just from spelling. The cadential six-four is spelled like a tonic, but because its bass is the dominant note and its upper tones resolve down into the dominant triad, the ear hears it as a tense, decorated dominant rather than a point of rest. The sixth and fourth behave exactly like suspensions: dissonances on a strong beat that resolve down by step on a weaker beat. Treating I6/4 as a stable tonic is the classic misanalysis; recognizing it as dominant function explains why it appears at cadences, why it falls on a strong beat, and why the chord that follows is the root-position V. This insight also generalizes: the next topic shows other six-four chords (passing, pedal) that are likewise not independent harmonies but decorations of a more stable chord.
Part-writing a cadential six-four
To write a cadential six-four, put the dominant note in the bass and double it, sound the sixth and fourth above it (the tonic and mediant), place it on a strong beat, then resolve the sixth down to the fifth and the fourth down to the third on a weaker beat to form V.
Try this
Q1. Which scale degree is in the bass of a cadential six-four, and is it held or moved? [1 point]
- Cue. Scale degree 5 (the dominant note) is in the bass and is held (and doubled) through the resolution to V.
Q2. Why is the cadential six-four analyzed as dominant function despite its tonic spelling? [2 points]
- Cue. Its bass is the dominant note and its sixth and fourth resolve down into the dominant triad, so the ear hears a decorated dominant, not a tonic.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2022 (style)1 marksSection I (multiple choice, written). In a cadential six-four (I6/4 to V), how do the sixth and the fourth above the bass resolve? (A) the sixth rises to a seventh and the fourth rises to a fifth (B) the sixth falls to a fifth and the fourth falls to a third (C) both stay as common tones (D) both rise by stepShow worked answer →
The correct answer is (B) the sixth falls to a fifth and the fourth falls to a third.
In a cadential six-four the bass is the dominant note (scale degree 5). Above it the sixth and the fourth are decorations that resolve down by step: the sixth (scale degree 1) falls to the fifth (scale degree 7, the leading tone), and the fourth (scale degree 3) falls to the third (scale degree 2), turning the chord into a true dominant.
(A) and (D) move the wrong direction. (C) holding both would leave the dominant undecorated. The trap is reading I6/4 as a stable tonic; it is really a decorated dominant, with the sixth and fourth resolving down to the fifth and third of V.
AP 2023 (style)3 marksSection II (free response, part-writing). In C major, part-write a cadential six-four to dominant (I6/4 to V), state the bass note, name the resolutions above the bass, and explain why the chord falls on a strong beat.Show worked answer →
A 3-point part-writing question.
(1 point) The bass note for both I6/4 and V is G (scale degree 5). Over the bass G, I6/4 sounds C and E (the sixth and fourth above G), with G doubled in the bass.
(1 point) Resolve to V (G, B, D): the sixth C falls to B (the leading tone), and the fourth E falls to D (the fifth of V); the bass G is held.
(1 point) The cadential six-four falls on a strong beat because it behaves like an accented dissonance (a double suspension) over the dominant; placing it on a strong beat and resolving to V on a weaker beat gives the characteristic leaning-then-resolving cadential sound.
Markers reward the bass on scale degree 5, the sixth resolving to the fifth (leading tone) and the fourth to the third, doubling the bass, and explaining the strong-beat placement.
Related dot points
- Topic 5.7 Additional 6/4 Chords: identify and part-write the passing six-four and the pedal (neighbor) six-four as embellishing chords over a stationary or stepwise bass.
A focused answer to AP Music Theory Topic 5.7, covering the passing six-four (bass passes by step between two positions of a chord) and the pedal or neighbor six-four (over a held bass), how each is an embellishing rather than functional chord, the smooth voice leading they need, and contrasting them with the cadential six-four, with a worked example.
- Topic 5.5 Cadences and Predominant Function: build complete cadential progressions with predominants and harmonise a given melody so it cadences correctly.
A focused answer to AP Music Theory Topic 5.5, covering full cadential progressions that include a predominant (such as I, IV or ii, V, I), how the predominant strengthens the approach to the cadence, and how to harmonise a given melody so the cadence lands correctly, with a worked harmonisation.
- Topic 4.3 Harmonic Progression, Functional Harmony, and Cadences: explain tonic, predominant and dominant function, the normal direction of progressions, and the four cadence types.
A focused answer to AP Music Theory Topic 4.3, covering functional harmony (tonic, predominant, dominant), the normal flow tonic to predominant to dominant to tonic, and the four cadences (perfect authentic, imperfect authentic, half, plagal, with the deceptive cadence), with a worked cadence analysis.
- Topic 4.4 Voice Leading with Seventh Chords: part-write the dominant seventh and other seventh chords in root position, resolving the chordal seventh and leading tone correctly.
A focused answer to AP Music Theory Topic 4.4, covering part-writing the dominant seventh in root position, resolving the chordal seventh down by step and the leading tone up, the option of an incomplete chord to avoid parallels, and preparing the seventh, with a worked resolution.
- Topic 4.2 SATB Voice Leading: apply the rules of range, spacing, doubling, smooth motion and tendency-tone resolution when writing four-part harmony.
A focused answer to AP Music Theory Topic 4.2, covering the four-voice ranges, the spacing rule (no more than an octave between adjacent upper voices), doubling guidelines, the ban on parallels and voice crossing, and resolving the leading tone and tendency tones, with a worked voicing.
Sources & how we know this
- AP Music Theory Course and Exam Description — College Board (2024)