Essential Triad Concepts

Why This Matters

Triads are the harmonic DNA of Western music—nearly every chord you'll encounter in your studies builds from these three-note structures. You're being tested not just on what triads are, but on how their construction creates different emotional effects and why composers choose one voicing over another. Understanding the relationship between intervals and triad quality unlocks your ability to analyze progressions, identify chords by ear, and write effective harmonies.

The concepts here connect directly to larger theory topics: chord progressions, voice leading, harmonic function, and cadences. When you see a triad on an exam, don't just name it—ask yourself what intervals built it, what quality it has, and how its position affects the musical context. Master the "why" behind each triad type, and you'll be ready for any identification or analysis question thrown your way.

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Triad Quality: How Intervals Create Character

The emotional "flavor" of a triad comes entirely from the intervals between its notes. The third determines major or minor quality; the fifth determines stability or tension. Learning to hear and construct these intervals is the foundation of all harmonic analysis.

Major Triads

• Root + major third + perfect fifth—the interval pattern that defines the bright, consonant major sound
• Stable and resolved quality makes major triads the harmonic "home base" in major keys
• Notation uses capital letters (C, G, D) or Roman numerals (I, IV, V) depending on context

Minor Triads

• Root + minor third + perfect fifth—the lowered third creates the characteristic darker sound
• Consonant but somber, minor triads function as stable chords in minor keys and add color in major keys
• Notation uses lowercase letters (c, g, d) or lowercase Roman numerals (i, iv, vi)

Diminished Triads

• Root + minor third + diminished fifth—both intervals are "small," creating maximum tension
• Unstable and dissonant, these triads demand resolution and typically function as leading-tone chords (vii°)
• Notation adds "dim" or ° (B°, Bdim) to indicate the altered fifth

Augmented Triads

• Root + major third + augmented fifth—the raised fifth creates an unsettled, "reaching" quality
• Symmetrical structure (two major thirds stacked) makes these triads harmonically ambiguous
• Notation adds "aug" or + (C+, Caug) and appears frequently in chromatic passages

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Triad Construction: Building from the Ground Up

Understanding how triads are assembled note-by-note gives you the tools to construct any chord from scratch. Every triad contains three scale degrees: root, third, and fifth—but the quality of those intervals changes everything.

Triad Construction (Root, Third, Fifth)

• The root names the chord—it's your reference point for measuring all other intervals
• The third determines quality—major third (4 half steps) = major; minor third (3 half steps) = minor
• The fifth provides stability—perfect fifth (7 half steps) anchors the chord; altered fifths create tension

Triad Quality Identification

• Count half steps from root to third first—this immediately tells you major (4) or minor (3)
• Then check the fifth—perfect (7), diminished (6), or augmented (8) half steps from the root
• Interval stacking shortcut: Major = M3 + m3; Minor = m3 + M3; Dim = m3 + m3; Aug = M3 + M3

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Triad Inversions: Same Notes, Different Bass

Inversions rearrange the same three notes by putting a different chord tone in the bass. The bass note changes the chord's stability, function, and how smoothly it connects to neighboring chords. This is essential for voice leading and figured bass analysis.

Root Position Triads

• Root in the bass—creates the most stable, grounded sound and strongest harmonic identity
• Figured bass: 5/3 (or no figures at all, since root position is the default)
• Best for establishing tonality at phrase beginnings and strong cadential arrivals

First Inversion Triads

• Third in the bass—lighter, more mobile sound that facilitates smooth bass lines
• Figured bass: 6/3 (often abbreviated to just "6")
• Creates stepwise bass motion when connecting root-position chords a third apart

Second Inversion Triads

• Fifth in the bass—the least stable inversion, often requiring special treatment
• Figured bass: 6/4—this symbol is your cue to check for cadential, passing, or pedal function
• Cadential $6/4$ chords precede dominant chords and resolve down by step in the bass

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Inversions in Musical Context: Why Voicing Matters

Knowing inversions isn't just about labeling—it's about understanding how voice leading and harmonic function work in real music. Composers choose inversions strategically to create smooth melodic lines in the bass and control harmonic tension.

Triad Inversions in Musical Context

• Voice leading efficiency—inversions allow all voices to move by step or small intervals rather than leaping
• Harmonic rhythm control—using inversions can soften chord changes or delay resolution for expressive effect
• Bass line melody—a well-crafted bass line often uses inversions to create its own coherent melodic shape

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Quick Reference Table

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Self-Check Questions

1. Which two triad types share a perfect fifth, and what single interval distinguishes them from each other?

2. You see a chord labeled "6/4" in a figured bass exercise—what three specific contexts might this chord appear in, and how does each function differently?

3. Compare and contrast diminished and augmented triads: how are their interval structures similar (both unstable), and how do their constructions differ?

4. If you're analyzing a passage and the bass line moves C → E → G while the harmony stays on C major, what sequence of inversions are you hearing?

5. A practice exam asks you to identify triad quality by ear. Describe the two-step interval-checking process you'd use, and explain why checking the third first is most efficient.