AP Music Theory Unit 5 ReviewChord Progressions and Predominant Function

AP Music Theory Unit 5 is where harmony stops being a two-chord game. You already know tonic and dominant; this unit adds predominant function, the chords (IV, iv, ii, ii°, and their seventh-chord versions) that sit between tonic and dominant and make the pull toward V much stronger. The single biggest idea is the function cycle tonic-predominant-dominant-tonic, which is the harmonic skeleton behind nearly every phrase you will analyze, hear, and part-write for the rest of the course. Along the way you also sort out the double life of the vi chord, the rare iii chord, new cadence types, and the four legal uses of second-inversion (6/4) chords.

What this unit covers

Predominant function: the bridge between tonic and dominant

• Composers intensify the sense of key by inserting predominant chords before the dominant, producing the standard order of functions tonic-predominant-dominant-tonic (T-PD-D-T).
• The main predominant triads are the subdominant (IV in major, iv in minor) and the supertonic (ii in major, ii° in minor). Both lead naturally into V.
• This fundamental progression is the harmonic background. The surface of real music orders chords in many combinations, but those combinations follow the historical conventions of tonal music, so the background T-PD-D-T pattern keeps showing up underneath.
• Predominant seventh chords (like ii7 or ii°7 with an added seventh) do the same job as the predominant triads. The new rule is voice-leading. The chordal seventh must resolve down by step, though it can be held in the same voice for a moment before resolving, as when ii7 moves to a cadential 6/4 before V.

The vi and iii chords: the supporting cast

• The vi (VI in minor) chord has two possible functions. It can act as a tonic substitute, standing in for I because it shares two notes with the tonic triad, or as a weaker predominant on its way to ii or IV.
• The tonic-substitute role of vi powers the deceptive progression, where V resolves to a chord other than tonic, typically vi. Your ear expects I, gets vi, and the phrase keeps going.
• The mediant triad (iii) is the wallflower of 18th-century harmony. It is rarely used in functional progressions in this style.
• The exception is in minor keys, where III most often appears representing the relative major key rather than functioning as a true mediant chord.

Cadences that use predominant function

• The plagal cadence moves IV to I (or iv to i), ending a phrase with predominant-to-tonic motion. Think of the "Amen" at the end of a hymn.
• The Phrygian half cadence is iv6 moving to V, and it happens only in minor keys. The bass descends by half step into the dominant, which gives it its distinctive sound.
• The deceptive cadence avoids the expected V-I resolution of an authentic cadence by substituting a non-tonic chord (usually vi) for the tonic.

The four 6/4 chord types

• Second-inversion triads are unstable in 18th-century style, so they appear only in four specific contexts: cadential, passing, pedal (or neighboring), and arpeggiated.
• The cadential 6/4 precedes the dominant, usually at a cadence, and sits in a metrically stronger position than the V that follows. Here is the trap. It contains the notes of the tonic triad, but it is NOT a tonic chord. It functions as an embellishment of the dominant.
• The passing 6/4 harmonizes the middle note of a three-note stepwise bass line (ascending or descending), filling in a bass passing tone, usually on a weak beat.
• The pedal (neighboring) 6/4 keeps the bass stationary while the third and fifth of a root-position triad step up to their upper neighbors and back, again usually on a weak beat.
• The arpeggiated 6/4 happens when the bass simply arpeggiates through the notes of one triad while the upper voices hold still. Only the bass moves.

Part-writing the 6/4 chords

• In a cadential 6/4, the sixth and fourth above the bass always resolve down by step. The figured bass 6/4 to 5/3 is literally a reminder of that voice leading.
• In a passing 6/4, double the fifth of the chord (the bass note) and keep all voices moving by step.
• In a pedal 6/4, the bass stays put while the upper neighbor tones decorate the chord and return.
• These rules show up in score analysis, error detection, writing exercises, and contextual listening, so you need to recognize them on the page and by ear, not just produce them.

Unit 5, Chord Progressions and Predominant Function at a glance

Why Unit 5, Chord Progressions and Predominant Function matters in AP Music

Unit 4 gave you the two poles of tonal harmony, tonic and dominant. Unit 5 fills in the space between them, which is where most of the actual music lives. The T-PD-D-T cycle is the lens the course uses for every harmonic skill from here on.

• Harmonic analysis stops being chord-by-chord labeling and becomes functional thinking. You group chords into tonic, predominant, and dominant zones, which is exactly how analysis prompts expect you to reason.
• Part-writing gets its standard recipe here. Most figured bass and Roman numeral writing tasks are built around a T-PD-D-T progression with a cadential 6/4 near the end.
• Harmonic dictation becomes possible once you can predict what comes next. Hearing a predominant tells you a dominant is coming, which narrows your options enormously.
• The 6/4 contexts train you to separate function from spelling, a skill the whole rest of the course leans on.

How this unit connects across the course

• Triad and seventh chord construction, qualities, and inversions (Unit 3) are the raw material here. You cannot label ii°6 or ii7 if you cannot spell and invert those chords quickly.
• Chord function, cadences, and phrase structure (Unit 4) introduced tonic and dominant and the authentic and half cadences. Unit 5 inserts the predominant stage between them and adds the plagal, Phrygian half, and deceptive cadences to your list.
• Embellishing tones (Unit 6) generalize what you learn from the linear 6/4 chords. The passing and pedal 6/4 are really passing tones and neighbor tones happening in multiple voices at once, so Unit 5 is a preview of that whole way of thinking.
• Secondary function (Unit 7) builds directly on the T-PD-D-T model by tonicizing chords other than I. You cannot hear V/V as special until the plain ii-V-I motion of this unit feels automatic.

Key notation and chord types

• Roman numerals with function labels (I, ii, IV, V, vi): uppercase for major, lowercase for minor, ° for diminished; the core analysis language for every progression.
• ii° and iv in minor: the minor-key predominants; ii° is diminished, so handle its doubling and inversion with care.
• Predominant seventh chords (ii7, ii°7, IV7): same function as the triads, but the chordal seventh must resolve down by step.
• Figured bass 6/4 and the 6/4 to 5/3 figures: the 6/4 marks a second-inversion triad, and 6/4 moving to 5/3 over the same bass note signals a cadential 6/4 with its required downward resolutions.
• Cadential 6/4 labeling: often written as I6/4 moving to V, but analyzed as part of the dominant, not as tonic.
• Cadence labels: plagal (IV-I or iv-i), Phrygian half (iv6-V, minor only), and deceptive (V to a non-tonic chord, usually vi).
• Inversion figures (6, 6/4, 6/5, 4/3, 4/2): tell you which chord member is in the bass; essential for reading and realizing figured bass lines.

Unit 5, Chord Progressions and Predominant Function on the AP exam

This unit's content is everywhere on the AP Music Theory exam because T-PD-D-T progressions are the default material for harmonic tasks.

• Multiple-choice questions, both aural and score-based, ask you to identify harmonic function, name cadence types, and classify which kind of 6/4 chord you are seeing or hearing. Expect questions where the answer hinges on knowing the cadential 6/4 is dominant function despite containing tonic notes.
• Harmonic dictation asks you to notate bass and soprano lines and supply Roman numerals for a progression you hear. Predominant chords, deceptive motion, and cadential 6/4 patterns are standard ingredients, so recognizing the sound of ii6 going to a cadential 6/4 going to V is a direct point-earner.
• Part-writing from figured bass requires you to realize figures like 6/4 to 5/3 correctly, resolving the sixth and fourth down by step and resolving chordal sevenths down.
• Part-writing from Roman numerals hands you a progression built on tonic, predominant, and dominant functions and grades your voice leading. Error-detection questions test the same rules in reverse by asking you to spot the broken resolution.
• Listening questions may ask you to identify a deceptive cadence or plagal cadence by ear, so practice hearing the "expected I, got vi" moment, not just spotting it on paper.

Essential questions

• Why does inserting a predominant chord before the dominant make the key feel more firmly established?
• How can one chord, like vi or the cadential 6/4, have a function that contradicts what its notes suggest?
• Why are second-inversion triads restricted to only four contexts in 18th-century style?
• What makes a cadence sound conclusive, evasive, or deceptive, and how does predominant function shape that effect?

Key terms to know

• Predominant function: the harmonic role of chords that lead to the dominant, filling the space between tonic and dominant in a progression.
• Subdominant (IV/iv): the triad built on scale degree 4, one of the two main predominant chords.
• Supertonic (ii/ii°): the triad built on scale degree 2, the other main predominant; diminished in minor keys.
• Tonic substitute: a chord (usually vi) that can stand in for the tonic because it shares most of its notes.
• Deceptive progression: dominant moving to a chord other than tonic, typically vi, frustrating the expected resolution.
• Plagal cadence: a phrase ending of IV-I (or iv-i), predominant resolving directly to tonic.
• Phrygian half cadence: iv6 moving to V in minor, with a half-step bass descent into the dominant.
• Cadential 6/4: a second-inversion chord on a strong beat before V that embellishes the dominant; its sixth and fourth resolve down by step.
• Passing 6/4: a 6/4 chord harmonizing the middle note of a three-note stepwise bass line, on a weak beat.
• Pedal (neighboring) 6/4: a 6/4 created by upper-neighbor motion over a stationary bass, on a weak beat.
• Arpeggiated 6/4: a 6/4 produced when the bass arpeggiates through its own triad while upper voices hold.
• Chordal seventh: the seventh above the root of a seventh chord, which normally resolves down by step.
• Harmonic background vs. foreground: the underlying T-PD-D-T skeleton versus the varied chord-by-chord surface composers build on top of it.

Common mix-ups

• The cadential 6/4 spells the tonic triad, but it is not tonic function. It belongs to the dominant. Labeling it as a structural I chord is one of the most common analysis errors in this unit.
• vi is not always a tonic substitute. After V it usually is (deceptive motion), but before ii or IV it is acting as a weak predominant. Read the context, not just the numeral.
• The Phrygian half cadence is minor-key only, and it is iv6 to V. Do not confuse it with a generic half cadence in major.
• Predominant function and the deceptive cadence are different things. IV and ii lead toward V; the deceptive cadence happens after V, when the resolution dodges the tonic.