Diatonic Seventh Chords

Why This Matters

Seventh chords are where harmony gets interesting—they're the difference between music that sounds like a hymnal and music that sounds like music. When you stack that extra third on top of a triad, you're adding tension, color, and forward motion that drives progressions toward resolution. You're being tested on your ability to identify these chord qualities by ear and on paper, understand their function within a key, and explain why certain chords create tension while others feel stable.

The real skill here isn't just naming chord types—it's understanding the intervallic structure that creates each chord's unique sound and recognizing how these chords function diatonically in major and minor keys. Every scale degree produces a specific seventh chord quality, and that pattern is completely predictable once you understand the underlying logic. Don't just memorize "ii is minor seventh in major"—know why the intervals stack that way and what role each chord plays in harmonic progressions.

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Stable Seventh Chords: The Points of Rest

These chords contain a major seventh interval from root to seventh, creating a sense of arrival and consonance. The major seventh's half-step proximity to the octave produces warmth without the urgent need to resolve.

Major Seventh Chord (maj7)

• Intervallic structure: root, M3, P5, M7—the most consonant of all seventh chord types
• Functions as tonic or subdominant in major keys, appearing naturally on scale degrees $\hat{1}$ and $\hat{4}$
• Notated as "maj7," "M7," or "Δ7" in lead sheets and jazz charts

Minor-Major Seventh Chord (mM7)

• Intervallic structure: root, m3, P5, M7—combines minor triad darkness with major seventh brightness
• Does not occur naturally in diatonic contexts; typically found in melodic minor harmony or as chromatic color
• Creates distinctive tension from the half-step between $\hat{5}$ and $\hat{7}$, often used for expressive effect in jazz ballads

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Tension-Building Seventh Chords: The Dominants

The dominant seventh chord is the engine of tonal harmony. Its defining feature is the tritone between the third and seventh, which creates an almost physical need to resolve.

Dominant Seventh Chord (7)

• Intervallic structure: root, M3, P5, m7—the tritone between $\hat{3}$ and $\hat{7}$ drives resolution to tonic
• Functions exclusively as V7 in diatonic major and harmonic minor contexts
• Notated simply as "7" (e.g., G7)—no prefix needed because dominant function is assumed

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The Minor Family: Soft Tension and Color

Minor seventh chords share a minor triad foundation but differ in their upper structure. The quality of the fifth and seventh determines whether the chord feels stable, tense, or somewhere in between.

Minor Seventh Chord (min7)

• Intervallic structure: root, m3, P5, m7—entirely built from minor thirds and a major third
• Functions as ii7, iii7, or vi7 in major keys; as i7 or iv7 in natural minor
• Notated as "min7," "m7," or "-7" depending on notation style

Half-Diminished Seventh Chord (ø7)

• Intervallic structure: root, m3, d5, m7—the diminished fifth adds instability to the minor seventh sound
• Functions as viiø7 in major and iiø7 in minor, typically moving toward dominant
• Notated as "ø7" or "m7♭5"—both symbols indicate the same chord quality

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Maximum Tension: The Diminished Seventh

The fully diminished seventh chord is pure instability—built entirely from minor thirds, it divides the octave into four equal parts, making its resolution ambiguous and powerful.

Fully Diminished Seventh Chord (°7)

• Intervallic structure: root, m3, d5, d7—symmetrical construction creates enharmonic ambiguity
• Functions as vii°7 in harmonic minor or as a chromatic passing/neighbor chord
• Notated as "°7" or "dim7"—the diminished seventh (d7) is enharmonically equivalent to a M6

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Diatonic Seventh Chord Patterns

Understanding which chord quality appears on each scale degree is essential for analysis. The pattern is determined entirely by the intervals available within the scale.

Seventh Chords in Major Keys

• Predictable pattern: Imaj7, ii7, iii7, IVmaj7, V7, vi7, viiø7—memorize this sequence
• Dominant seventh occurs only on $\hat{5}$ because that's the only degree with both M3 and m7 above it
• Half-diminished on $\hat{7}$ due to the naturally occurring diminished fifth between $\hat{7}$ and $\hat{4}$

Seventh Chords in Minor Keys

• Natural minor pattern: i7, iiø7, IIImaj7, iv7, v7, VImaj7, VII7—note the minor v7 lacks dominant function
• Harmonic minor raises $\hat{7}$, transforming v7 into V7 and creating vii°7 instead of VIImaj7
• The raised $\hat{7}$ creates the leading tone necessary for authentic cadences in minor

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Inversions and Voice Leading

Inversions change the bass note without changing the chord's identity. Smooth voice leading often depends on choosing the right inversion to minimize leaps.

Seventh Chord Inversions

• Four positions possible: root position, first ($^6_5$), second ($^4_3$), and third ($^4_2$) inversions
• Figured bass numbers indicate intervals above the bass, not the chord's root
• Third inversion ($^4_2$) places the seventh in the bass, creating strong downward resolution tendency

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Quick Reference Table

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Self-Check Questions

1. Which two seventh chord types share a minor triad foundation but differ in their fifth? What scale degrees do they typically appear on in major keys?

2. Compare the dominant seventh and major seventh chords: what single interval difference explains why one resolves and the other doesn't?

3. Why does natural minor lack true dominant function, and which scale modification fixes this problem? Name the specific chords affected.

4. If you see a chord labeled $^4_3$ in figured bass, what inversion is it, and which chord tone is in the bass?

5. A student claims that vii°7 and viiø7 are interchangeable. Explain which keys each chord belongs to diatonically and how their sound differs.