Which chord is described as a diminished triad plus a diminished seventh?

• A. Diminished Seventh Chord
• B. Half Diminished Seventh Chord
• C. Diminished Triad Plus Diminished Seventh
• D. Dominant Seventh Chord

Answer: (A)

The idea is building chords by stacking thirds and naming the intervals above the root. A diminished triad has root, minor third, and diminished fifth. If you add a note that is a diminished seventh above the root, you get a four-note chord with each step a minor third apart (0, 3, 6, 9 semitones). This four-note sonority is called a fully diminished seventh chord, commonly shortened to diminished seventh chord. It’s different from a half-diminished seventh, which uses a minor seventh above the root, and from a dominant seventh, which uses a major triad with a minor seventh. So describing it as a diminished triad plus a diminished seventh corresponds exactly to the diminished seventh chord.