Key Harmonic Functions

Why This Matters

Understanding harmonic functions is the key to unlocking how tonal music actually works. Rather than seeing chords as isolated events, you'll learn to hear them as players in a drama—each with a specific role that creates tension, stability, or forward motion. On the exam, you're being tested on your ability to identify these functions in context, explain why a progression feels inevitable or surprising, and analyze how composers manipulate expectations to create emotional impact.

These functions connect directly to larger concepts in harmonic analysis: voice leading, cadential patterns, tonicization, and large-scale tonal structure. When you encounter an FRQ asking you to analyze a passage, the graders want to see that you understand the functional logic driving the harmony—not just chord labels. So don't just memorize which Roman numerals belong to which function; know what each function does and how it interacts with the others to create musical meaning.

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Pillars of Stability and Motion

Every tonal piece operates on a fundamental tension between rest and movement. These three primary functions form the backbone of Western harmony, each playing a distinct role in the push-and-pull that makes music feel alive.

Tonic Function

• Serves as the tonal center—the "home base" represented by the I chord (or i in minor), where phrases typically begin and end
• Provides resolution and stability—the gravitational center that all other harmonies orbit around
• Establishes key identity—without a clear tonic function, listeners lose their sense of orientation in the harmonic landscape

Dominant Function

• Creates maximum tension seeking resolution—the V chord contains the leading tone ($\hat{7}$), which pulls strongly toward $\hat{1}$
• Drives harmonic motion forward—the tritone between $\hat{4}$ and $\hat{7}$ in V7 creates instability demanding resolution
• Essential for authentic cadences—the V–I progression is the most powerful confirmation of key in tonal music

Subdominant Function

• Provides contrast and departure—the IV chord moves away from tonic without the urgent pull of dominant
• Contains $\hat{4}$, which pulls toward $\hat{3}$—this tendency tone creates gentle motion back toward tonic territory
• Enriches the harmonic palette—offers a "softer" alternative path in progressions, especially in plagal motion

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Setting Up the Dominant

Before the dominant can do its job, other chords prepare its arrival. Pre-dominant function creates the anticipation that makes dominant resolution feel earned rather than abrupt.

Pre-dominant Function

• Encompasses chords leading to V—most commonly ii (or ii° in minor) and IV
• Creates the T–PD–D–T paradigm—this four-stage model describes the fundamental logic of tonal progression
• The ii chord is particularly strong—shares two notes with IV but includes $\hat{6}$, which pulls down to $\hat{5}$ in the dominant

Subdominant Function (as Pre-dominant)

• IV frequently serves pre-dominant purposes—moves smoothly to V through stepwise bass motion ($\hat{4}$ to $\hat{5}$)
• Less "urgent" than ii—provides a broader, more expansive sound before dominant arrival
• Common in popular and folk styles—the IV–V–I progression remains a cornerstone of Western music

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Marking Structural Boundaries

Cadences are the punctuation marks of music. Understanding cadential function helps you identify phrase structure and explain how composers create—or deny—closure.

Cadential Function

• Signals phrase endings through specific progressions—V–I (authentic), IV–I (plagal), V–vi (deceptive), V or I6/4–V (half)
• Perfect authentic cadence (PAC) is strongest—requires root position V–I with soprano arriving on $\hat{1}$
• Cadence type affects structural weight—PACs close sections definitively; half cadences create "comma" effects mid-phrase

Deceptive Function

• Dominant resolves to unexpected chord—typically V–vi, substituting the relative minor for expected tonic
• Creates surprise while maintaining forward motion—vi shares two notes with I, softening the "deception"
• Extends phrases and delays closure—composers use this to build tension before the "real" resolution arrives

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Expanding and Extending Harmony

Not every chord represents a new function. Some harmonies exist to prolong or elaborate an underlying function, creating surface variety without changing the deeper harmonic meaning.

Prolongation Function

• Extends a single harmony through embellishment—the underlying function persists even as surface chords change
• Techniques include passing chords, neighbor chords, and pedal tones—these create motion without functional progression
• Essential for Schenkerian analysis—distinguishes between structural harmonies and their elaborations

Pedal Point Function

• Sustained or repeated bass note beneath changing harmonies—most commonly on $\hat{1}$ (tonic pedal) or $\hat{5}$ (dominant pedal)
• Creates tension between static bass and mobile upper voices—the pedal "anchors" while harmonies float above
• Dominant pedals build anticipation—frequently appear before final cadences, intensifying the eventual resolution

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Expanding Tonal Boundaries

These functions take us beyond the home key, either temporarily or permanently. They're essential for understanding how composers create variety and large-scale harmonic drama.

Secondary Dominant Function

• Dominant chord targeting a non-tonic chord—labeled V/x or vii°/x, where x is the chord being tonicized
• Temporarily tonicizes a diatonic chord—borrows the "pull" of dominant function to strengthen arrival on a new chord
• Common targets include V/V, V/ii, and V/vi—adds chromatic color and intensifies motion to the target chord

Modulation Function

• Changes the tonal center to a new key—goes beyond temporary tonicization to establish a new tonic
• Pivot chord modulation uses a chord common to both keys—the smoothest transition between tonal areas
• Direct modulation moves abruptly without pivot—creates dramatic effect through sudden key change

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Quick Reference Table

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Self-Check Questions

1. Comparative function: Both ii and IV can serve pre-dominant function. What voice-leading difference makes ii particularly strong in classical style, and when might IV be preferred?

2. Identify by concept: A passage sustains $\hat{5}$ in the bass for eight measures while upper voices move through various harmonies. What function is this, and what effect does it create?

3. Compare and contrast: Explain the difference between a secondary dominant (V/vi) resolving to vi and a deceptive cadence (V–vi). How do their functions differ even though both involve V and vi?

4. FRQ-style application: A phrase ends with V–vi instead of the expected V–I, then continues for four more measures before reaching a PAC. How would you describe the function of the V–vi motion in terms of phrase structure?

5. Conceptual identification: You're analyzing a passage where the harmony moves from I to IV to V to I. Label each chord's function, then explain what would change functionally (not just in chord quality) if the IV were replaced by ii.