A one-page visual summary of Chord Progressions and Predominant Function — every predominant chord, cadence, and six-four type you need to know for the exam, on a single screen.
What it covers: Filling in predominant function — IV/iv and ii/ii°, the tonic-substitute vi, the rare iii, predominant seventh chords, the Phrygian half cadence, and every type of six-four chord.
Exam weight: AP Music Theory is weighted by section, not by unit (45% multiple choice, 45% free response, 10% sight-singing). Units 4–7 (harmony and voice leading) dominate the free-response part-writing and analysis.
The big question: How do predominant chords and six-four chords extend the basic T–PD–D–T model into fuller, more expressive progressions?
Big Ideas covered: Pitch (BI 1), Form (BI 3), Music Design (BI 4).
Key topics at a glance
Predominant Chords
IV/iv and ii/ii° sit between tonic and dominant in the T–PD–D–T model, building momentum toward the cadence.
The vi Chord
A tonic substitute sharing two notes with I. Most famous as the target of the deceptive cadence (V–vi).
Predominant Sevenths
ii7 (minor 7th, major keys) and iiø7 (half-diminished, minor keys). The chordal 7th still resolves down by step.
The iii Chord
Rare in this style — it shares notes with both I and V, making its function ambiguous. Mostly appears as a passing chord.
New Cadence: Phrygian Half
In minor, iv⁶ → V with the bass falling a half step — a half cadence with a distinctive Phrygian-mode flavor.
Cadential Six-Four
I⁶₄ right before V. Spelled like tonic but functions as V — its 6th and 4th resolve down by step into the dominant.
Other Six-Fours
Passing (connects chords a 3rd apart), neighboring (bass stays put), arpeggiated (bass leaps within one chord) — all decorative, not new functions.
Metric Placement
A cadential 6/4 sits on a strong beat, resolving to V on a weaker beat — proof it's decorating the dominant, not standing as tonic.
The key terms you must know
T–PD–D–T model — the standard harmonic skeleton: tonic, predominant, dominant, tonic.
Predominant function — the role of IV/iv and ii/ii°, building toward the dominant.
Tonic substitute — a chord (like vi) that can stand in for I because it shares tonic-chord tones.
Deceptive cadence — V resolving to vi instead of the expected I.
Phrygian half cadence — iv⁶–V in minor, with the bass falling a half step.
Cadential six-four — I⁶₄ immediately before V; functions as a dominant embellishment.
Passing six-four — connects two chords a third apart via stepwise bass motion.
Neighboring (pedal) six-four — bass stays fixed while upper voices decorate with neighbor tones.
Arpeggiated six-four — bass simply leaps through the notes of one chord.
Key themes to remember
Predominant chords have a job. IV/iv and ii/ii° exist to lead into the dominant — think of them as the "setup," not a destination.
vi is not a random minor chord. Its shared tones with I make it a genuine substitute for tonic.
A 6/4 spelling doesn't guarantee tonic function. Context (what comes before and after, and where it falls metrically) determines the real function.
Not every six-four does the same thing. Cadential embellishes V; passing, neighboring, and arpeggiated all embellish a single harmony.
Sevenths still resolve down. Predominant seventh chords follow the same rule as any seventh chord — the 7th falls by step.
Common exam traps
Don't label a cadential 6/4 as "I." Even though it's spelled I, it functions as an embellished V — label it I⁶₄ moving to V, not as an independent tonic arrival.
Passing vs. neighboring vs. arpeggiated — check the bass. Passing bass moves stepwise between two different chords; neighboring bass stays on one note; arpeggiated bass leaps within one chord.
iii is not interchangeable with I or V. Even though it shares tones with both, don't assume it can substitute freely — it's genuinely rare and ambiguous.
Phrygian half cadence needs iv⁶, not iv. The characteristic half-step bass motion requires the chord's inversion.
ii° vs. ii7's quality changes by mode. In minor, the supertonic triad is diminished (ii°), so its seventh chord is half-diminished (iiø7) — don't default to the major-key ii7 quality.