Unit 5: The Phrase Model and Predominant Harmonies

The Harmonic Phrase Model

To understand Unit 5, you must master the fundamental grammar of Western functional harmony: the Phrase Model. This model dictates the logical flow of chord progressions that establish a key.

The standard progression follows this trajectory:

1. Tonic (T): Establishes stability ($I$ or $i$).
2. Predominant (PD): moves away from the tonic and prepares the dominant ($IV$, $iv$, $ii$, $ii^\circ$).
3. Dominant (D): Creates maximum tension requiring resolution ($V$ or $V^7$).
4. Tonic (T): Resolution and return to stability.

T \rightarrow PD \rightarrow D \rightarrow T

The Role of Predominant Function

Predominant Function (or pre-dominant) refers to chords that bridge the gap between stability (Tonic) and tension (Dominant). While the Tonic can move directly to the Dominant ($I - V$), inserting a Predominant chord expands the phrase and strengthens the arrival of the Dominant.

• Key Characteristic: They share scale degrees with the Tonic (giving a sense of departure) and the Dominant (providing smooth voice leading).
• Primary Chords: The Subdominant ($IV/iv$) and the Supertonic ($ii/ii^\circ$).

The Subdominant Chord ($IV$ and $iv$)

The Subdominant triad is built on the 4th scale degree (${4, 6, 1}$). It creates a sense of moving away from home without the urgent "leading tone" pull of the Dominant.

Quality and Usage

• Major Keys ($IV$): A Major triad.
• Minor Keys ($iv$): A Minor triad.
• Function: It typically leads to $V$ or $vii^\circ$. It can also appear in the Plagal Cadence ($IV - I$), commonly known as the "Amen" cadence, though this ends a phrase rather than preparing the dominant.

Voice Leading: The $IV \rightarrow V$ Danger Zone

Moving from $IV$ to $V$ is one of the most dangerous movements in AP Music Theory part-writing due to the stepwise root motion.

The Problem:
If the Bass moves up by step ($4 \rightarrow 5$) and the upper voices also move up, you will almost certainly create Parallel 5ths and Parallel 8ves.

The Solution:
Use Contrary Motion. If the bass moves UP by step, the Upper Voices (Soprano, Alto, Tenor) should move DOWN to the nearest chord tone of V.

• Bass: Moves up ($Fa \rightarrow Sol$)
• Upper Voices: Move down to the nearest chord tones.

The Supertonic Chord ($ii$ and $ii^\circ$)

The Supertonic triad is built on the 2nd scale degree (${2, 4, 6}$). It is widely considered a stronger predominant than the $IV$ chord because its root moves to the Dominant by a descending 5th (a very strong harmonic motion).

Quality varies by Key Mode:

The Supertonic in First Inversion ($ii^6$ and $ii^{\circ6}$)

In part-writing and the AP exam, the first inversion supertonic is often preferred over the root position, especially in minor keys.

1. Usage in Major ($ii^6$): The bass is scale degree 4. It functions similarly to a $IV$ chord but with a different root.
2. Usage in Minor ($ii^{\circ6}$):
   • In minor keys, the $ii^\circ$ is a diminished triad.
   • Diminished triads are rarely used in root position because of the dissonant tritone with the bass.
   • Rule: Always use $ii^\circ$ in first inversion ($ii^{\circ6}$) to place the chordal third (a consonant interval) in the bass.

Doubling Rules for $ii^6$

When writing a $ii^6$ (or $ii^{\circ6}$), the bass note is the chordal third.

• Standard Doubling: Double the Bass (the third of the chord).
• Why? The bass allows for smooth voice leading and reinforces the subdominant flavor (since the bass note is scale degree 4).

The Cadential Six-Four Chord ($I^6_4$)

Although it looks like a Tonic chord, the Cadential Six-Four functions as Dominant harmony. It is vital for Unit 5 voice leading.

Concept

The $I^6_4$ acts as a "double suspension" or decoration of the $V$ chord. It delays the arrival of the dominant tones.

• Notation: It is often analyzed as $V^{6-5}_{4-3}$.
• Bass: Scale degree 5 (Dominant note).
• Upper Voices: Scale degrees 1 and 3 (which are a 4th and 6th above the bass).

AP Exam Guidelines for $I^6_4$

1. Metrical Placement: Must occur on a Strong Beat (stronger than the $V$ that follows it).
2. Resolution:
   • The 6th above the bass (scale degree 3) resolves down to the 5th (scale degree 2).
   • The 4th above the bass (scale degree 1) resolves down to the 3rd (leading tone).
3. Doubling: Always double the Bass (scale degree 5).

Voice Leading: Predominant to Dominant ($ii \rightarrow V$)

Connecting the Supertonic to the Dominant involves specific voice-leading strategies.

Common Tone Retention

Unlike $IV \rightarrow V$, the progression $ii \rightarrow V$ shares a common tone (scale degree 2).

1. Keep the Common Tone: Ideally, keep the common tone in the same voice (usually Alto or Tenor).
2. Move Other Voices: Move the remaining voices stepwise to the nearest chord tones of $V$.
3. Leading Tone: Ensure the resulting $V$ chord contains the leading tone (scale degree 7). In minor keys, you MUST accidentally raise the leading tone.

Handling Seventh Chords ($ii^7 \rightarrow V$)

If using a supertonic seventh chord (very common):

• Preparation: The 7th of the $ii^7$ is usually prepared by common tone or step.
• Resolution: The 7th of the chord MUST resolve down by step.

Summary of Harmonic Progressions

When harmonizing a melody or realizing a figured bass, utilize these standard predominant strings:

1. Basic: $I - IV - V - I$
2. Stronger Root Motion: $I - ii^6 - V - I$
3. Cadential Extension: $I - ii^6 - I^6_4 - V - I$ (The "Classic" AP progression)
4. Minor Key: $i - iv - V - i$ or $i - ii^{\circ6} - V - i$

Common Mistakes & Pitfalls

1. Parallel 5ths/8ves in $IV \rightarrow V$

• Mistake: Moving all voices upward when the bass moves $4 \rightarrow 5$.
• Correction: Use contrary motion. If Bass goes up, Soprano/Alto/Tenor should generally move down.

2. Incorrect Doubling in $ii^6$

• Mistake: Doubling the root in a first inversion supertonic chord.
• Correction: In $ii^6$ (and especially $ii^{\circ6}$), double the Bass (scale degree 4). This avoids doubling the tritone tones in minor keys.

3. Misunderstanding the $I^6_4$

• Mistake: Labeling a $I^6_4$ based on its notes (C-E-G) as a Tonic function.
• Correction: If the bass is scale degree 5 and it resolves to $V$, it is a Dominant function. Always write it as part of the dominant block.

4. Forgetting the Accidental in Minor

• Mistake: Writing a $ii^{\circ6} \rightarrow V$ in minor but forgetting to raise the definition of the leading tone in the $V$ chord.
• Correction: In harmonic minor, scale degree 7 must be raised to create a major $V$ chord.

5. Root Position $ii^\circ$

• Mistake: Writing a diminished supertonic triad in root position ($ii^\circ$).
• Correction: Diminished triads should almost always be in first inversion ($ii^{\circ6}$) to soften the dissonance.