Questions: Triad Quality: Diminished and Augmented

Question 1

Which intervals make up a diminished triad built on C?

• A. A diminished 3rd (C to E♭♭) and a diminished 5th (C to G♭)
• B. A minor 3rd (C to E♭) and a diminished 5th (C to G♭) — equivalently, two stacked minor thirds
• C. A minor 3rd (C to E♭) and a minor 5th (C to G♭)
• D. A major 3rd (C to E) and a diminished 5th (C to G♭)

Answer: (B)

A diminished triad is built by stacking two minor thirds: C→E♭ (minor 3rd, 3 half steps) and E♭→G♭ (another minor 3rd, 3 half steps). The outer span C→G♭ is a diminished 5th (6 half steps, the tritone). Option D is a common mistake — major 3rd plus diminished 5th would not stack evenly. The key: diminished triad = m3 + m3, outer span = diminished 5th. Compare to major (M3 + m3) and minor (m3 + M3), both of which span a perfect 5th.

Question 2

An augmented triad sounds ambiguous and tonally unstable. What is the structural reason for this?

• A. The augmented triad is missing the root, so the ear cannot identify a tonal center
• B. The augmented triad contains a major 3rd that clashes with the bass note
• C. Two stacked major thirds create an augmented 5th (8 half steps) that divides the octave symmetrically into three equal parts, removing any clear directional pull toward resolution
• D. The augmented triad is always chromatic, and chromatic chords are inherently unstable

Answer: (C)

An augmented triad (C–E–G♯) consists of two equal major thirds, and all three inversions are enharmonically equivalent — C–E–G♯, E–G♯–C, and G♯–C–E all contain the same interval content. This symmetry means the ear cannot identify a definitive root or a preferred direction of resolution. Contrast with the diminished triad, whose tritone creates a strong, directed pull toward specific resolution tones. The augmented triad hovers ambiguously, which composers like Liszt exploited for tonal transitions.

Question 3

An augmented triad is built with a major 3rd and an augmented 3rd stacked above the root.

• T. True
• F. False

Answer: False

This is the most common misconception about augmented triads. An augmented triad is built with a MAJOR 3rd on the bottom and another MAJOR 3rd on top (not an augmented 3rd). On C: C–E (major 3rd) and E–G♯ (major 3rd again). The outer span is an augmented 5th (8 half steps). The word 'augmented' in the triad name refers to the augmented 5th outer span, not to an augmented 3rd.

Question 4

Both diminished and augmented triads are unstable, but they are unstable in different ways: the diminished triad pulls strongly toward resolution, while the augmented triad creates ambiguity without a clear directional pull.

• T. True
• F. False

Answer: True

The diminished triad's instability is directed — the tritone between its outer notes creates a convergent pull: the diminished 5th wants to resolve inward (both notes moving toward a more stable interval). This is why the leading-tone triad (vii°) drives powerfully toward the tonic. The augmented triad's instability is non-directed — its symmetric structure (three equal thirds) means no single resolution is implied more strongly than another, creating a hovering, ambiguous quality rather than a forward-pulling one.

Question 5

Major and minor triads both span a perfect 5th between root and fifth; diminished and augmented triads deviate from this. Explain how these deviations produce the characteristic sound of each non-standard triad quality.

Model answer: The perfect 5th is the most acoustically stable interval after the octave, and its presence in major and minor triads gives them their grounded, resolved quality. The diminished triad contracts this fifth to a diminished 5th (tritone), which is maximally unstable — both outer notes pull toward adjacent pitches, creating strong directed tension. The augmented triad expands to an augmented 5th (8 half steps), which is symmetric (three equal major thirds) and has no strong directional pull, creating hovering ambiguity instead of directed tension.

The outer fifth is the structural backbone of a triad. When it is perfect, the chord is stable; when it is altered, instability results. But the *kind* of instability differs: diminished = directed (resolves strongly), augmented = ambiguous (no clear resolution). Understanding this helps explain why diminished chords are used at cadence points (their tension drives toward tonic) while augmented chords are used for harmonic ambiguity and modulation.