Tonicization through Secondary Leading Tone Chords - AP Music Theory Study Guide

Getting Started

You have learned how diatonic chords function within a key, particularly how the leading-tone chord (vii°) creates tension that resolves to the tonic (I). This chapter expands on that principle, showing how we can apply the same leading-tone function to chords other than the tonic. This process, called tonicization, allows us to temporarily treat a non-tonic chord as a point of arrival, adding chromatic color and harmonic interest to a piece of music.

What You Should Be Able to Do

• Identify secondary leading-tone chords in notated and performed music.

• Provide a correct Roman numeral analysis for a secondary leading-tone chord, including its target.

• Describe how a secondary leading-tone chord creates the effect of tonicization.

• Spell a secondary leading-tone triad or seventh chord that tonicizes a given major or minor triad in a specific key.

• Distinguish between a diatonic leading-tone chord and a secondary leading-tone chord.

Key Concepts & Analysis

Our analysis of secondary leading-tone chords is guided by the principles of Functional Harmony. This lens views harmony as a progression of functions—Tonic (stability), Pre-Dominant (moving away from tonic), and Dominant (creating tension that leads back to tonic). Secondary leading-tone chords are a special type of dominant-function chord.

Functions & Allowable Motions

Tonicization is the process of making a non-tonic chord sound like a temporary tonic. This is achieved by preceding it with a chord that has a dominant function relative to it.

A secondary leading-tone chord is a dominant-function chord whose root is the leading tone of the chord being tonicized. It creates a strong pull toward that target chord, making it sound, for a moment, like a point of arrival or a temporary tonic.

• Core Function: The function of any secondary leading-tone chord is Dominant. It creates tension that demands resolution to its target chord. We can label this function as D/X, meaning "dominant of X," where X is the Roman numeral of the target chord.

• Harmonic Grammar: The fundamental motion is from the secondary leading-tone chord to its target chord. This creates a miniature D → T progression within the larger piece. For example, in the progression I - viio⁶/V - V, the viio⁶/V - V part functions as a temporary D - T relationship in the key of the dominant.

• Notation: We write these chords as $\text{viio/X}$ or ${\text{viio}}^7/extX$. This is read as "vii diminished of X" or "vii diminished seven of X." The 'X' is the Roman numeral of the major or minor triad being tonicized. For example, ${\text{viio}}^6/\text{V}$ is "vii diminished six of five."

Structure and Inversion Rules

The construction of a secondary leading-tone chord is precise and follows specific rules based on common-practice harmony.

• Target Chords: Any diatonic major or minor triad may be tonicized. In a major key, this includes ii, iii, IV, V, and vi. In a minor key, this includes III, iv, V, and VI. Diminished triads (like vii° in major or ii° in minor) are not tonicized.

• Triads (${\text{viio}}^6/extX$): A secondary leading-tone triad is a diminished triad. It appears only in first inversion. This places the third of the chord in the bass, which creates a smoother bass line and avoids the dissonant interval of a diminished fifth between the bass and an upper voice.

• Seventh Chords (${\text{viio}}^7/extX$): A secondary leading-tone seventh chord is a diminished seventh chord. Depending on the key signature and the target chord, it may be a half-diminished seventh (ø7) or a fully-diminished seventh (°7). Unlike the triads, these seventh chords may appear in any inversion (root position, 6/5, 4/3, or 4/2).

Common Progressions

Secondary leading-tone chords are used to intensify the arrival of the chord they precede. They are woven directly into standard harmonic progressions.

• In C major, tonicizing V (G major): I - viio⁶/V - V (C - F♯dim⁶ - G)

• In C major, tonicizing ii (d minor): I - viio⁷/ii - ii⁶ (C - C♯°⁷ - Dm⁶)

• In a minor, tonicizing iv (d minor): i - viio⁶/iv - iv (Am - C♯dim⁶ - Dm)

• In a minor, tonicizing V (E major): i - viio⁷/V - V (Am - D♯°⁷ - E)

Data & Organization Tools

This function map illustrates how secondary leading-tone chords fit into the T-PD-D-T harmonic grammar. They act as a "dominant of the next chord," intensifying the forward motion of the progression.

Harmonic Function Map

• Tonic (T): I, i

• Pre-Dominant (PD): IV, iv, ii, ii°

• Dominant (D): V, V⁷, vii°, vii°⁷

• Secondary Dominant Function (D/X): V/X, V⁷/X, $\text{viio/X}$, ${\text{viio}}^7/extX$

Typical Functional Paths:

• Basic Path: T → PD → D → T

• Path with Tonicization: T → (D/PD) → PD → D → T (e.g., I - viio⁷/ii - ii - V - I)

• Path with Tonicization: T → PD → (D/D) → D → T (e.g., I - IV - viio⁶/V - V - I)

Evidence Bank

• Tonicization: The musical process of making a non-tonic chord sound like a temporary tonic, typically by preceding it with its own dominant-functioning chord.

• Secondary Leading-Tone Chord: A chord built on the leading tone of a temporary tonic. Its function is to create a strong pull toward that target chord.

• Notation: $\text{viio/X}$: The standard Roman numeral label for a secondary leading-tone chord. "vii°" indicates a diminished triad, and "/X" specifies the target chord (e.g., /V, /ii, /IV).

• Target Chords: The chords that can be tonicized. These must be major or minor triads within the primary key.

• Triad Inversion Rule (${\text{viio}}^6/extX$): Secondary leading-tone triads must be in first inversion. The root position is not used in this style.

• Seventh Chord Inversions: Secondary leading-tone seventh chords (${\text{viio}}^7/extX$) are flexible and may appear in any inversion, including root position.

• Root of the Chord: The root of a secondary leading-tone chord is always a chromatic pitch that acts as the leading tone to the root of the target chord.

• Chord Quality: The chord is a diminished triad or a diminished seventh chord (either half-diminished or fully-diminished).

Skill Snapshots

Functional

1. Progression:I - viio⁶/V - V

   Why it works: The ${\text{viio}}^6/\text{V}$ functions as the dominant of V, creating a powerful resolution that strengthens the arrival of the primary dominant chord.

2. Progression:i - viio⁷/iv - iv

   Why it works: In a minor key, tonicizing the subdominant (iv) with its leading-tone chord adds chromaticism and intensifies the move into the pre-dominant function.

3. Progression:I - viio⁶/vi - vi

   Why it works: This progression makes the arrival of the submediant (vi) more dramatic and significant, often used to initiate a new phrase or section.

Voice-Leading

1. Rule: The root of the secondary leading-tone chord (the temporary leading tone) almost always resolves up by half step to the root of the target chord.

   Effect: This stepwise resolution is the primary driver of the tonicizing effect, creating a powerful sense of arrival.

2. Rule: The tritone (augmented fourth or diminished fifth) found within the secondary leading-tone chord resolves according to standard voice-leading practice.

   Effect: The resolution of this inherent dissonance into the stable consonant intervals of the target chord provides a feeling of release and harmonic satisfaction.

3. Rule: The required first inversion for triads (${\text{viio}}^6/extX$) places the third of the chord in the bass.

   Effect: This creates a smoother, often stepwise bass line and avoids the harsh sound of a diminished fifth between the bass and an upper voice.

Form

1. Baseline Phrase: A simple phrase ending in an authentic cadence: I - IV - V - I.

2. Contrast: The same phrase with tonicization: I - IV - viio⁶/V - V - I. The cadence type remains authentic, but the harmonic path to the dominant is made more compelling and chromatic.

3. Continuity: A composer might use tonicization consistently throughout a piece to establish a rich harmonic language. For example, an antecedent phrase might tonicize the subdominant (...viio⁶/IV - IV...), while the consequent phrase tonicizes the dominant (...viio⁶/V - V...).

Common Misconceptions & Clarifications

• Misconception: Confusing a secondary leading-tone chord with a diatonic one.

  Clarification: The diatonic vii° chord is built on the 7th scale degree of the home key. A secondary leading-tone chord, like $\text{viio/V}$, is built on the 7th scale degree of the dominant's scale. In C major, vii° is B-diminished, while $\text{viio/V}$ is F♯-diminished.

• Misconception: Forgetting that secondary leading-tone triads must be in first inversion.

  Clarification: The label $\text{viio/X}$ is shorthand; in analysis, it must be written as ${\text{viio}}^6/extX$. Seventh chords are more flexible and can appear in any position.

• Misconception: Believing that tonicization is the same as a modulation (a key change).

  Clarification: Tonicization is a brief, localized event that strengthens a diatonic chord. The music remains firmly in the home key. A modulation is a more structural shift to a new key, confirmed by a strong cadence in that new key.

• Misconception: Thinking that diminished chords can be tonicized.

  Clarification: Only major and minor triads serve as stable targets for tonicization. The inherent instability of a diminished triad makes it an unsuitable temporary tonic.

Summary

Secondary leading-tone chords are chromatic chords that create tonicization by functioning as the dominant of a major or minor triad other than the tonic. Labeled as $\text{viio/X}$ or ${\text{viio}}^7/extX$, their root is the leading tone of the chord they are tonicizing. These chords are always diminished in quality. While the seventh chords can appear in any inversion, the triads are used exclusively in first inversion (${\text{viio}}^6/extX$) to ensure smooth voice leading. By temporarily elevating a non-tonic chord to the status of a tonic, these chords add harmonic depth, color, and a stronger sense of forward momentum to musical progressions. They are a key tool for moving beyond simple diatonic harmony.