Questions: Triad Construction: Major, Minor, and Diminished

Question 1

D-F#-A is a D major triad. Which change produces a D minor triad?

• A. Lower the fifth from A to Ab, keeping the third at F#
• B. Lower the third from F# to F natural, keeping the fifth at A
• C. Raise the third from F# to G, keeping the fifth at A
• D. Lower both the third and the fifth by one semitone

Answer: (B)

A minor triad differs from a major triad only in the quality of the third — the fifth remains a perfect fifth in both. Lowering F# to F natural changes the interval from root to third from a major third (4 semitones) to a minor third (3 semitones), producing D-F-A: a D minor triad. The fifth (A) stays put. Option A would produce a diminished-like chord; option D would move both, changing the fifth to a diminished fifth.

Question 2

What makes the diminished triad fundamentally different from both major and minor triads?

• A. It is built on only two notes instead of three
• B. Its fifth is a diminished fifth (tritone, 6 semitones) rather than a perfect fifth (7 semitones)
• C. It can only be built starting on the note B
• D. It is the same as a minor triad with the notes in reverse order

Answer: (B)

Both major and minor triads share a perfect fifth (7 semitones) from root to fifth — what distinguishes them is only the quality of the third. The diminished triad is structurally different: it stacks two minor thirds (3 + 3 semitones), producing a diminished fifth (6 semitones, a tritone) from root to fifth. This unstable interval is why the diminished triad sounds tense and cannot serve as a stable resting point, unlike major or minor triads.

Question 3

Both major and minor triads have a perfect fifth from root to fifth; they are distinguished only by whether the third above the root is a major third (4 semitones) or a minor third (3 semitones).

• T. True
• F. False

Answer: True

This is the key structural insight. Major: M3 (4 semitones) + m3 (3 semitones) = P5. Minor: m3 (3 semitones) + M3 (4 semitones) = P5. Same outer interval, different middle note position. The diminished triad, by contrast, breaks this pattern: m3 + m3 = d5 (6 semitones), not a perfect fifth.

Question 4

A triad's quality (major, minor, or diminished) depends on which root note you start from — chords built on C are naturally major because C is the 'natural' home key in Western music.

• T. True
• F. False

Answer: False

Triad quality is determined entirely by interval structure, not by the root note. You can build any quality on any root. C-E-G is major, but C-Eb-G is minor, and C-Eb-Gb is diminished — all starting on C. The root determines the pitch level; the intervals between the notes determine the quality. This is the foundational principle of chord construction.

Question 5

Why do major and minor triads sound emotionally different even though both contain a perfect fifth from root to fifth?

Model answer: The difference lies in where the middle note (the third) is positioned within the perfect fifth. In a major triad, the major third (4 semitones) sits below the minor third (3 semitones) — the bottom interval is wider, creating a more open, upward-leaning quality. In a minor triad, the minor third (3 semitones) sits below the major third — the bottom is compressed, creating a more inward or downward-leaning quality. This difference in interval weight produces distinct acoustical characters (bright vs. dark) rooted in the overtone series and reinforced by centuries of Western musical convention.

The emotional quality is not arbitrary or purely cultural — it has acoustic roots in how close the chord tones are to the natural harmonic series. But it is also deeply shaped by learned convention. Understanding this gives you the ability to predict how listeners will perceive any chord you build, and it explains why the major-minor distinction is so central to tonal music.