Unit 5 Harmony Skills: Building Functional Progressions with Predominants and Six-Four Chords

Common Chord Progressions

A chord progression is a purposeful ordering of chords that creates musical direction. In AP Music Theory, you’re usually working in common-practice tonal harmony (roughly Bach through early Romantic styles), where progressions are guided by harmonic function—the idea that chords tend to behave like characters in a story: some feel like “home,” some create motion away from home, and some create strong pull back home.

Harmonic function: the “grammar” behind progressions

In most tonal phrases, chords fall into three broad functional families:

  • Tonic function: stability and arrival (most commonly I, sometimes vi or iii depending on context)
  • Predominant function: preparation and motion toward dominant (most commonly ii and IV, plus variants like ii⁶)
  • Dominant function: tension and drive toward tonic (V, V⁷, vii°⁶, and related dominants)

Why this matters: on the AP exam, you’re not just naming chords—you’re showing you understand how they connect. If you choose “legal” voice-leading between random chords but the progression doesn’t behave functionally, it will sound unstylistic and you’ll lose points in part-writing contexts.

A common functional “sentence” is:

  • Tonic → Predominant → Dominant → Tonic

That basic pattern underlies many of the progressions you’ll see in Roman numeral analysis and many of the progressions you’ll be expected to write in four-part harmony.

Common progression archetypes (and why they work)

Rather than memorizing long lists, it’s better to understand a few archetypes and what they’re trying to accomplish.

1) Authentic harmonic motion: I → (predominant) → V → I

This is the core engine of tonal music. Predominant chords (especially ii or IV) increase momentum toward V by introducing scale degrees that “want” to resolve in dominant harmony.

  • Predominant chords often include scale degree 4 (in major) or scale degree 6 (in minor), which help set up dominant tension.
  • Dominant harmony contains the leading tone (scale degree 7), which strongly pulls to tonic.

In action (Roman numerals):

  • In C major: I (C) → ii (Dm) → V (G) → I (C)
  • In A minor (harmonic minor behavior is typical around V): i (Am) → iv (Dm) → V (E or E7) → i (Am)
2) The “prolongation” idea: extending tonic before moving on

Progressions often prolong tonic—meaning they extend the feeling of I without leaving the tonic area in a major way.

Common tonic-prolonging moves include:

  • I → I⁶ → I (neighboring motion in the bass)
  • I → vi → ii → V → I (vi can feel like a tonic substitute early in the phrase)

Why it matters: students sometimes label every non-I chord as “predominant,” but vi is often tonic-functioning when it appears early and doesn’t clearly push to V.

In action:

  • In G major: I (G) → vi (Em) → ii (Am) → V (D) → I (G)
3) Root motion by fifth: the “strongest” directional motion

A major reason tonal progressions feel logical is that roots often move by descending fifth (or ascending fourth), which reinforces tonal hierarchy.

Examples of fifth-related root motion:

  • ii → V
  • V → I
  • vi → ii
  • iii → vi

A longer chain (common in sequences) might look like:

  • iii → vi → ii → V → I

Even if you don’t explicitly think “circle of fifths,” you can often predict what chord comes next by asking: “What chord would prepare or intensify the move toward V and then I?”

How to use progression patterns in part-writing

When you’re writing SATB (soprano, alto, tenor, bass) in AP style, you’re balancing two things:

  1. Functional harmony (progression makes sense)
  2. Correct voice leading (individual lines make sense)

A practical approach:

  1. Decide your cadence goal (often a PAC, IAC, or HC depending on the prompt).
  2. Work backward: if you want an authentic cadence, you’ll likely need V (or V⁷) before I.
  3. Insert a predominant before V (ii or IV are your defaults).
  4. Fill in tonic-prolonging chords near the beginning if needed.

Worked example: analyzing a short phrase

Suppose you see a bass line in C major that goes:

  • C → A → D → G → C

A common functional harmonization is:

  • C: I
  • A: vi (tonic-prolonging / tonic-substitute)
  • D: ii (predominant)
  • G: V (dominant)
  • C: I (tonic)

Notice how the bass roots A → D → G → C outline a strong chain of fifth-related motion starting at vi.

What goes wrong: common progression misconceptions

A few classic traps:

  • Using predominant after dominant: In common-practice style, predominant typically comes before dominant. A move like V → ii usually sounds like you backed up the harmonic “story.” It can happen in some contexts, but it’s not the default AP-style choice.
  • Overusing iii: iii is diatonic, but in four-part writing it can be awkward and often functions as a passing/connecting harmony. It’s not a “go-to” predominant.
  • Treating every second-inversion triad as a normal chord: Many 6-4 chords are embellishing and must resolve in specific ways (you’ll study these in the Six-Four section below).
Exam Focus
  • Typical question patterns:
    • Identify the function of a chord within a progression (tonic vs predominant vs dominant) in Roman numeral analysis.
    • Choose the most stylistic chord to complete a progression leading to a cadence.
    • Harmonize a bass line where root motion suggests a common progression (often involving vi and ii).
  • Common mistakes:
    • Writing progressions that skip predominant function entirely before a strong dominant arrival (result can sound abrupt).
    • Mislabeling vi as predominant in early-phrase tonic prolongation contexts.
    • Creating correct-looking Roman numerals that don’t match the actual chord spelling in the given key.

Predominant Chords (ii, IV)

Predominant function is the harmonic “setup” that prepares dominant. A predominant chord typically intensifies motion away from tonic and aims you toward V (or vii°). In AP Music Theory, your primary predominant chords are ii and IV (including their common inversions and, in minor, their common altered forms).

What predominant chords are (and why they matter)

In a tonal phrase, you usually want the dominant to feel earned. Predominants help by:

  • Introducing scale degrees that lead smoothly into the dominant chord tones
  • Increasing harmonic tension without reaching the peak tension of dominant
  • Providing good bass-line motion into V (especially ii → V)

If tonic is “home” and dominant is “the cliffhanger that demands resolution,” predominant is the part of the story where things start to shift—momentum builds and the phrase becomes goal-directed.

The ii chord: the default predominant

The ii chord is built on scale degree 2. In major it is minor (ii), and in minor it is diminished (ii°) if built strictly diatonically.

ii in major

Example in C major:

  • ii = D–F–A

Why it works so well: ii shares two notes with V⁷ in many contexts and tends to move smoothly into dominant.

ii in minor: what you need to watch

In a natural minor collection, ii is diminished (ii°), which is less stable as a plain triad. In common-practice harmony, minor-key predominant usage often favors:

  • iv (minor iv) as a strong predominant
  • ii°⁶ as a common predominant sonority (especially in first inversion)

Students often struggle here because “ii in minor” does not behave exactly like “ii in major.” In AP-style part writing, ii° in root position is less common than ii°⁶ because first inversion avoids an unstable diminished fifth in the bass and tends to voice-lead more smoothly.

The IV chord: the other main predominant

The IV chord is built on scale degree 4.

In C major:

  • IV = F–A–C

IV often feels slightly broader or more “plagal” than ii, but it still functions predominantly when it leads toward V. One reason IV is so useful: it gives you a different palette and can support common melodic tendencies (for example, scale degree 6 in the soprano can sit naturally in IV).

Predominant inversions: why ii⁶ is so common

In four-part writing, ii⁶ (first inversion) is extremely common. The reason is mostly voice-leading and bass-line smoothness:

  • ii⁶ places scale degree 4 in the bass (in major), which often moves stepwise down to scale degree 3 or up to 5 depending on context.
  • It can avoid awkward leaps and help you create a more singable bass.

Example in C major:

  • ii⁶ = F–A–D (with F in the bass)

Even though the bass note changes, the chord is still ii—your Roman numeral shows inversion with the figured bass “6.”

How predominant chords lead into dominant (voice-leading targets)

To write convincing predominant-to-dominant motion, you want to think about tendency tones and common tones.

  • In major, predominant often contains scale degree 4, which frequently resolves to scale degree 3 (especially in inner voices) or participates in motion toward dominant.
  • Dominant harmony includes scale degree 7 (leading tone) that resolves to 1.

A useful mindset: predominant should “aim” at dominant chord tones by step when possible.

Example: ii⁶ → V in C major (conceptual voice-leading)
  • ii⁶ (F–A–D) to V (G–B–D)
  • Notice D can be held as a common tone (ii has D; V has D).
  • F often moves to G or to E depending on voicing goals.
  • A often moves to G or B depending on spacing and avoiding parallels.

This is why ii (especially ii⁶) is such a reliable setup for V.

Worked progression examples (with functional explanation)

Example 1: I → ii⁶ → V⁷ → I in C major
  • I (C–E–G): establishes tonic
  • ii⁶ (F–A–D): predominant preparation; smooth bass if you choose F in bass
  • V⁷ (G–B–D–F): dominant peak tension
  • I (C–E–G): resolution

Common pitfalls to avoid while voicing:

  • Don’t double tendency tones in ways that make resolution difficult (for example, doubling the leading tone in V).
  • Make sure the chordal seventh in V⁷ resolves down by step.
Example 2: I → IV → V → I in G major
  • I (G–B–D)
  • IV (C–E–G)
  • V (D–F#–A)
  • I (G–B–D)

This is a “textbook” functional progression. It’s also a good reminder that IV is genuinely predominant when it leads to V, not just “the plagal chord.”

What goes wrong: typical predominant errors

  • Using IV as a tonic substitute in a dominant-aiming spot: IV can sometimes feel like a coloristic expansion, but if the phrase is clearly moving to a cadence, IV should behave like a predominant and lead cleanly to V.
  • Treating ii° in minor like ii in major: In minor keys, be especially careful about spelling (raised leading tone affects V, not necessarily ii) and about inversion choice (ii°⁶ is common; ii° root position is less common in basic chorale style).
  • Incorrect chord spelling vs. incorrect Roman numeral: You can’t “force” a ii label onto a chord that doesn’t match scale degree 2 in the key.
Exam Focus
  • Typical question patterns:
    • Given a progression, identify which chord(s) have predominant function and justify by context (what they lead to).
    • Part-writing prompts that strongly imply ii⁶ or IV before V near a cadence.
    • Roman numeral analysis requiring correct quality in minor (recognizing ii° and iv, and common inversions).
  • Common mistakes:
    • Writing ii in minor with the wrong quality or using it in an unstable inversion without good voice-leading.
    • Doubling the leading tone in dominant after a predominant, making resolution almost impossible to do cleanly.
    • Forgetting that predominant function is largely contextual—ii doesn’t “do its job” if it doesn’t actually lead to dominant.

Six-Four Chords

A six-four chord (written 6/4 or just “6-4”) is a triad in second inversion, meaning the fifth of the chord is in the bass. The name comes from the intervals you see above the bass: a fourth and a sixth.

Six-four chords are a big deal in AP Music Theory because they look like ordinary triads on paper but often behave more like embellishments than independent functional harmonies. In other words, the Roman numeral label alone is not enough—you also need to understand the type of 6-4 and how it should resolve.

What a 6-4 chord is (and why it’s special)

If you take a root-position triad and put the fifth in the bass, you get second inversion.

Example: C major triad

  • Root position: C–E–G (C in bass)
  • First inversion: E–G–C (E in bass)
  • Second inversion: G–C–E (G in bass) = I 6/4

Why it matters: the 4th above the bass is considered unstable in common-practice voice-leading. As a result, many 6-4 chords require specific resolutions—often by step—so they don’t sound like you’ve placed a dissonance and forgotten to resolve it.

A useful mental model: most 6-4 chords are not “destination” chords; they are events that decorate or intensify a more stable harmony.

The main types of 6-4 chords you need to recognize

AP Music Theory commonly emphasizes these categories:

  1. Cadential 6-4
  2. Passing 6-4
  3. Pedal 6-4
  4. Arpeggiated 6-4

Each type is defined less by the chord’s pitch content and more by its bass behavior and resolution.

Cadential 6-4: the most important one

A cadential 6-4 occurs at a cadence and intensifies the dominant. It is typically not treated as a true tonic chord—even if it’s written as I 6/4—because it functions as a decoration of V.

How it works

At a cadence in major, you often see:

  • I 6/4 → V (or V7) → I

Even though the first chord contains tonic pitches, the bass is scale degree 5 (because it’s second inversion), and the 6 and 4 above that bass usually resolve into chord tones of V.

In C major:

  • I 6/4 over G in the bass contains G–C–E
  • V over G in the bass contains G–B–D

The crucial voice-leading idea:

  • The “4” above the bass (C above G) typically resolves down to B.
  • The “6” above the bass (E above G) typically resolves down to D.

So the upper voices often move down by step into the dominant harmony.

Why it matters

Cadential 6-4 is one of the most tested 6-4 types because:

  • It’s common
  • It’s easy to mislabel functionally
  • It has characteristic resolutions that are graded in part-writing

A very common mistake is to treat I 6/4 like a stable tonic and then voice it freely. In strict chorale style, it should behave like a dominant expansion with careful resolutions.

Passing 6-4: stepwise bass motion creates the inversion

A passing 6-4 occurs when the bass moves stepwise and the harmony in second inversion fills in between two more stable harmonies.

A classic pattern is:

  • I → V6/4 → I6 (in a tonic-prolongation context)

In this pattern:

  • The bass moves stepwise (for example 1–2–3 or 3–2–1 depending on inversion choices).
  • The 6-4 chord is literally “passing” between two stable chords.

What to listen/look for:

  • Stepwise bass
  • Smooth voice-leading where the upper voices often also move by step
  • The 6-4 sonority is brief and connects two stable points

Pedal 6-4: bass stays the same, upper voices move

A pedal 6-4 happens when the bass holds (a pedal tone) while the upper voices move, creating a 6-4 sonority as a neighbor embellishment.

Typical context:

  • You might have V in the bass sustained, while upper voices move to create a I 6/4 sonority above that bass and then return.

What to look for:

  • Same bass note across the surrounding harmonies
  • The 6-4 appears because upper voices move away and back

This can happen on dominant (common) or tonic pedals.

Arpeggiated 6-4: outlining a single harmony

An arpeggiated 6-4 occurs when a single chord is prolonged by arpeggiating its chord tones in the bass.

Example idea:

  • A tonic harmony might be extended with bass notes that outline the tonic triad (1–3–5), creating I, I6, and I6/4 as part of a single tonic expansion.

Key idea: the function doesn’t change as much as the inversion does—this is about prolongation and texture rather than a functional shift.

How to label 6-4 chords (Roman numerals plus context)

In AP analysis, you will often:

  • Identify the chord and inversion (for example, I 6/4)
  • Identify the type by context (cadential, passing, pedal, arpeggiated)

A cadential 6-4 is sometimes annotated to show its dominant connection (you may see it discussed as part of a dominant expansion). Even if you still label the pitches as I 6/4, you should think “dominant decoration” when you voice-lead it.

Worked examples: recognizing types by bass motion

Example 1: Cadential 6-4 in C major

Bass: G → G → C

  • Over the first G: I 6/4 (G–C–E)
  • Over the second G: V (G–B–D) or V7 (G–B–D–F)
  • Then to C: I

Recognition clues:

  • Occurs right before V at a cadence
  • Bass sits on scale degree 5 through the 6-4 into V
  • Upper voices resolve down by step into V
Example 2: Passing 6-4 in G major (tonic prolongation)

Bass: G → A → B

  • Over G: I
  • Over A: V 6/4 (a passing sonority in this context)
  • Over B: I6

Recognition clues:

  • Bass moves stepwise
  • The 6-4 is between two tonic-functioning chords (I and I6)
  • The goal is smooth connection, not cadential dominant emphasis

(Exact chord labels depend on the pitches provided, but the diagnostic feature is the stepwise bass and “in-between” placement.)

What goes wrong: the big 6-4 pitfalls

  • Treating any 6-4 as stable: In chorale style, second inversion is rarely “free.” You typically need a reason (cadential, passing, pedal, arpeggiated).
  • Incorrect resolution in cadential 6-4: If the 4th and 6th above the bass don’t resolve properly into V, the cadence won’t sound stylistic.
  • Misidentifying type by chord label alone: I 6/4 can be cadential, passing, pedal, or arpeggiated. The bass motion and placement in the phrase tell you which.
Exam Focus
  • Typical question patterns:
    • Identify and label a 6-4 chord by inversion and type (especially cadential 6-4) in Roman numeral analysis.
    • Part-writing near a cadence where a cadential 6-4 is the expected embellishment before V.
    • Error-detection items where the given 6-4 fails to resolve correctly.
  • Common mistakes:
    • Writing a cadential I 6/4 but spacing/voice-leading it like a normal tonic chord (instead of resolving into V).
    • Forgetting that second inversion requires contextual justification, leading to “random” 6-4 usage.
    • Doubling or resolving tones in a way that creates parallel fifths or octaves when moving from 6-4 to V.