Unit 4 Overview: Functional Harmony and Musical Structure

Understanding Harmonic Function

In tonal music, chords are not random events; they follow a specific grammar or syntax known as Functional Harmony. This system dictates how chords progress from stability to tension and back to stability. Understanding this flow is essential for part-writing (FRQs 5 and 6) and harmonic dictation.

The Three Main Functions

Broadly speaking, every chord in a key can be categorized into one of three functional families. The standard progression of functional harmony is:

Tonic $\rightarrow$ Predominant $\rightarrow$ Dominant $\rightarrow$ Tonic

1. Part I: The Tonic Function (Stability)

• Role: The home base. It represents rest, stability, and resolution.
• Primary Chord: I (Major) or i (minor).
• Substitute: vi or VI (often used in Deceptive Cadences to prolong the phrase).

2. Part II: The Dominant Function (Tension)

• Role: The conflict or tension that demands resolution. The defining characteristic is the presence of the Leading Tone (scale degree 7), which pulls strongly upward to the Tonic (scale degree 1).
• Primary Chord: V and V$^7$ (the strongest dominant chords).
• Substitute: vii$^o$ or vii$^{o7}$ (leading-tone chords).

3. Part III: The Predominant (Subdominant) Function (Preparation)

• Role: Bridges the gap between Tonic and Dominant. It sets up the tension.
• Primary Chords: IV (iv) and ii (ii$^o$).
• Note: In AP Music Theory, the supertonic (ii) is considered a stronger predominant than the subdominant (IV) because its root movement to V is a descending 5th (strong root movement).

Key Concept: You generally do not move backward from Dominant to Predominant (D $\rightarrow$ S). This is called a "retrogression" and is usually avoided in Common Practice style.

Cadences: The Punctuation of Music

A Cadence is a harmonic goal—a resting point at the end of a phrase. Think of cadences as punctuation marks (periods, commas, question marks). Identifying cadences requires looking at the last two chords of a musical phrase.

1. Authentic Cadences (V $\rightarrow$ I)

The most conclusive cadence type. It represents a full stop.

Perfect Authentic Cadence (PAC)

Ideally, this is the strongest finish in music.

• Progression: V $\rightarrow$ I (or V$^7$ $\rightarrow$ I).
• Condition A: Both chords must be in Root Position.
• Condition B: The Soprano must end on Scale Degree 1 (Do) in the final chord.

Imperfect Authentic Cadence (IAC)

Still V $\rightarrow$ I, but "weaker" because it fails one of the PAC tests.

• One or both chords are inverted.
• The Soprano ends on Scale Degree 3 (Mi) or 5 (Sol).

2. The Half Cadence (Ends on V)

This sounds like a question mark or a comma. It feels unfinished and demands a continuation.

• Progression: Anything $\rightarrow$ V.
• The most common approach is I $\rightarrow$ V or IV $\rightarrow$ V.

The Phrygian Half Cadence

A specific type of half cadence found only in minor keys.

• Progression: iv$^6$ $\rightarrow$ V.
• Voice Leading: The bass moves down by half-step ($Le \rightarrow Sol$) while the soprano usually moves up by whole step ($Fa \rightarrow Sol$). This contrary motion is highly characteristic.

3. The Plagal Cadence (IV $\rightarrow$ I)

Often called the "Amen" cadence. It creates a sense of "post-resolution" rather than active resolution, as it lacks the leading tone.

• Progression: IV $\rightarrow$ I (or iv $\rightarrow$ i).

4. The Deceptive Cadence (V $\rightarrow$ vi)

The "Psych Out." The ear expects the V to resolve to I, but it goes to the submediant (vi/VI) instead.

• Progression: V $\rightarrow$ vi (Major) or V $\rightarrow$ VI (minor).
• Voice Leading Rule: In a V $\rightarrow$ vi progression, the leading tone in the soprano MUST resolve up to tonic to avoid augmented intervals.

Phrase Structure and Period Form

A Phrase is a substantial musical thought that ends with a cadence. Generally, phrases are 4 measures long, though they can vary.

The Period

A Period is a pair of phrases that work together in an "Antecedent-Consequent" (Question-Answer) relationship.

• Phrase 1 (Antecedent): Ends with a weak cadence (usually a Half Cadence or IAC).
• Phrase 2 (Consequent): Ends with a strong cadence (usually a PAC) that feels more final than the first.

$Period = Weak\ Cadence + Strong\ Cadence$

Types of Periods

To identify the type of period, compare the melodic material at the beginning of both phrases.

1. Parallel Period ($a$ … $a'$)

• The second phrase begins with the same melody as the first phrase (or very similar).
• Example: Phrase 1 starts with a specific motif; Phrase 2 starts with that same motif but alters the ending to achieve a stronger cadence.

2. Contrasting Period ($a$ … $b$)

• The second phrase begins with different melodic material than the first.
• Despite the difference in melody, they still function as a pair because of the weak-strong cadence relationship.

Memory Aid: The Cadence Checklist

When analyzing a cadence, ask these questions in order:

1. Does it end on V? $\rightarrow$ Half Cadence (Check Bass: is it $iv^6$ to $V$ in minor? Then Phrygian).
2. Does it end on vi? $\rightarrow$ Check previous chord. If V $\rightarrow$ vi, it's Deceptive.
3. Does it end on I? $\rightarrow$ Check previous chord.
   • If IV $\rightarrow$ I: Plagal.
   • If V $\rightarrow$ I: Authentic.
     • Drill Down: Is the soprano on Do? Roots in bass? Yes = PAC. No = IAC.

Common Mistakes & Pitfalls

1. Confusing the Phrygian Half Cadence:

   • Mistake: Calling any minor key cadence ending on V "Phrygian."
   • Correction: It implies a specific bass motion: iv$^6$ to V. If the bass doesn't move scale degree $6 \rightarrow 5$, it is just a standard Half Cadence.

2. Misidentifying PACs:

   • Mistake: Seeing a V going to I and automatically labeling it a PAC.
   • Correction: Always check the Soprano voice. If the soprano ends on the 3rd or 5th of the chord, it is an IAC, even if it sounds strong.

3. The "vii°" Trap:

   • Mistake: Thinking a cadence must use V.
   • Correction: vii$^o$ $\rightarrow$ I is also considered an Authentic cadence (usually IAC) because it has Dominant function resolving to Tonic, though V $\rightarrow$ I is standard.

4. Period Identification:

   • Mistake: Identifying a "Period" just because there are two phrases.
   • Correction: A Period strictly requires the weak-to-strong cadence relationship. If Phrase 1 ends in a PAC and Phrase 2 ends in a PAC, that is a "Phrase Group," not a Period, because there is no sense of unresolved tension leading to resolution.