5.7 Additional 6/4 chords

Beyond the cadential ⁶₄, there are three more second inversion chords you need to recognize and write: neighboring (pedal), passing, and arpeggiated ⁶₄ chords. All of these are weak, embellishing chords that decorate a stronger harmony instead of building real harmonic progress, and each has its own doubling and voice leading pattern.

Why This Matters for the AP Music Theory Exam

⁶₄ chords have historically tripped up AP Music Theory students, so knowing all four types gives you a real edge. In this topic you learn to describe and label the type of ⁶₄ chord in notated music, then apply 18th-century voice leading to passing, pedal (neighboring), and arpeggiated ⁶₄ chords through score analysis, error detection, writing exercises, and contextual listening.

That shows up in several exam tasks:

• Spotting and labeling ⁶₄ types when you analyze a score.
• Catching doubling and parallel-motion mistakes during error detection.
• Adding a bass line to a soprano melody and supplying Roman and Arabic numerals, where the right ⁶₄ in the right spot keeps the implied progression strong.
• Hearing the difference between an embellishing ⁶₄ and a true change of harmony in dictation.

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Key Takeaways

• ⁶₄ chords appear in only four contexts: cadential, neighboring (pedal), passing, and arpeggiated. All are embellishing, not harmony-building.
• Neighboring (pedal) ⁶₄: the bass stays put while the third and fifth of a root-position triad move up to their upper neighbors, then back. Usually on a weak beat.
• Passing ⁶₄: harmonizes a passing tone in the bass during a three-note stepwise line. Double the fifth, keep all voices stepwise, place it on a weak beat.
• Arpeggiated ⁶₄: the bass arpeggiates the triad (or rocks between root and fifth) while the upper voices stay static. Common in waltzes and marches, usually on a weak beat.
• Beat placement is a rule, not a suggestion: cadential ⁶₄ goes on a strong beat; passing and neighboring ⁶₄ go on weak beats.
• When you imply harmony from a soprano and bass, avoid weak chord successions like V-IV, V-ii, ii-iii, IV-iii, ii-I, V-vi⁶, and iii-vii°.

The Four ⁶₄ Chord Types

A second-inversion (⁶₄) triad sounds weak because its tonic, dominant, or subdominant quality fades when the fifth is in the bass. Try it at a keyboard: play a I chord in C major, then put the fifth (G) in the bass. The chord loses much of its solid tonic feel. That weakness is exactly why ⁶₄ chords work as embellishments rather than as full members of a progression. You already learned the cadential ⁶₄ in the last topic, where a I⁶₄ decorates the dominant before resolving to V. The other three types are below.

Neighboring or Pedal ⁶₄ Chords

The pedal ⁶₄ chord, also called the neighboring ⁶₄ chord, occurs when the third and fifth of a root-position triad are embellished by their upper neighbor tones while the bass stays the same.

For example, in A♭ major you can embellish two root-position I chords with a pedal ⁶₄. Because the bass must stay the same for all three chords, the middle chord ends up being a IV⁶₄: the bass of the tonic triad in A♭ major is A♭, and the bass of the second-inversion IV chord is also A♭. The upper voices of the I chord (C and E♭) move up by step to their neighbors (D♭ and F) for the ⁶₄ chord, then return.

When you part write a pedal ⁶₄, keep the bass stationary and move the third and fifth of the root-position triad to their upper neighbors and back. This chord usually lands on a weak beat.

Passing ⁶₄ Chords

A passing tone is a non-chord tone that fills the gap between two notes a third apart, creating smooth stepwise motion. A passing ⁶₄ harmonizes a passing tone in the bass.

Say you are in the tonic area with a I chord moving to a I⁶ chord. The bass goes from the tonic up to the mediant. To make that bass line stepwise, you can add the supertonic in between, giving a three-note ascending scale fragment. Now you want chords that fit that middle note without changing the harmony. A ii chord pulls toward predominant function and a vii⁶ pulls toward dominant function, which would feel like a sudden harmonic detour inside a tonic area. The weak option that does not disturb the harmony is a V⁶₄ between the two tonic chords. That is a passing ⁶₄ chord.

Because all ⁶₄ chords are weak, dropping a V⁶₄ between two tonic chords does not really sound like a tonic-dominant-tonic move. It sounds like a tonic chord, some connecting tones, and then another tonic chord, so you keep a strong tonic feel while adding melodic interest in the bass.

In practice you might see a I-V⁶₄-I⁶ progression giving an ascending stepwise bass (for example E♭-F-G in E♭ major).

Voice Leading with Passing ⁶₄ Chords

• Double the fifth of the ⁶₄ chord.
• Move all voices by step into and out of the chord.
• Place the chord on a weak beat. In 4/4 with quarter notes, the passing ⁶₄ often falls on beat two, weaker than the surrounding beats that carry the tonic chords.

When the upper voices move stepwise while the bass moves the opposite direction, you often create a clean voice exchange between soprano and bass.

Arpeggiated ⁶₄ Chords

An arpeggio is a broken chord whose notes are played in sequence, like C-E-G ascending or G-E-C descending. The arpeggiated ⁶₄ chord appears when the bass arpeggiates a triad while the three upper voices stay static.

For example, a I chord followed by a I⁶ moves the bass from tonic to mediant. Add a I⁶₄ to complete the arpeggiation, and the bass spells tonic-mediant-dominant while the upper voices hold their notes. The bass can also just oscillate between the root and fifth of the chord. Keep the upper voices stationary so only the bass moves, and place the ⁶₄ on a weak beat.

This pattern is common in waltzes (3/4 time), where a strong downbeat is followed by lighter upbeats. Arpeggiated ⁶₄ chords are most often built on I, and arpeggiated V⁶₄ chords also appear. They show up rarely on other diatonic chords.

How to Use This on the AP Music Theory Exam

Score Analysis

Label each ⁶₄ by what the surrounding voices and bass are doing, not just by its notes:

• Bass holds still, upper voices step up and back: neighboring (pedal).
• Bass moves stepwise through a passing tone: passing.
• Bass arpeggiates the chord while upper voices hold: arpeggiated.
• ⁶₄ on a strong beat decorating V before resolving: cadential.

Error Detection

Watch for the doubling and motion that each type requires. In a passing ⁶₄, the fifth should be doubled and every voice should move by step. Also check for parallel or hidden fifths and octaves when the bass moves into or out of any ⁶₄.

Part Writing and Implied Harmony

When you add a bass line under a soprano melody, the harmony you imply has to stay plausible. Keep rhythmic placement correct: cadential ⁶₄ on a strong beat, passing and neighboring ⁶₄ on weak beats. Avoid these weak successions:

• V-IV
• V-ii
• ii-iii
• IV-iii
• ii-I
• V-vi⁶
• iii-vii°

These mostly move backward through the tonic-predominant-dominant-tonic flow, which weakens the progression. Also avoid root-position vii°, vi⁶, and iii⁶ unless they fit a specific exception such as a modulation or an acceptable diatonic sequence with parallel first-inversion chords.

Common Trap

Treating a ⁶₄ chord as a real harmonic event. A V⁶₄ passing between two tonic chords does not change the prevailing harmony, so do not analyze it as a true dominant arrival.

Common Misconceptions

• "A V⁶₄ or I⁶₄ functions like a normal V or I." Second-inversion triads are weak and almost always embellish a stronger harmony. The bass note and surrounding voice leading tell you the real function.
• "All ⁶₄ chords go on weak beats." Passing, neighboring, and arpeggiated ⁶₄ chords typically fall on weak beats, but the cadential ⁶₄ lands on a stronger beat than the dominant it decorates.
• "In a passing ⁶₄ you double the root." Double the fifth, and move every voice by step.
• "You can use any chord to harmonize a passing tone in the bass." A ii or vii⁶ adds too much harmonic pull. You want a weak ⁶₄ that does not redirect the progression.
• "Arpeggiated ⁶₄ chords only work on the tonic." They are most common on I, and V⁶₄ versions appear too, but other diatonic chords are rare.
• "vi⁶ and iii⁶ are just normal chords to use." They are generally avoided in this style unless they belong to a specific exception like a modulation or an accepted sequence.

Related AP Music Theory Guides

• 5.1 Adding Predominant Function IV (iv) and ii (ii0) to a Melodic Phrase
• 5.6 Cadential 6/4 Chords
• 5.5 Cadences and Predominant Function
• 5.4 The iii (III) Chord
• 5.3 Predominant Seventh Chords
• 5.2 The vi (VI) Chord