Three minor third intervals stacked together produce which kind of chord?

• A. A major triad
• B. A minor seventh chord
• C. A diminished seventh chord
• D. A augmented triad

Answer: (C)

Stacking minor third intervals on a root bass creates a chord whose successive steps are all minor thirds, giving a four-note chord whose top note is a diminished seventh above the root. This configuration is called a fully diminished seventh chord. For example, starting on C you get C, Eb, Gb, and Bbb (enharmonically A). Each pair of adjacent notes is a minor third apart, so the interval from the root to the top note is a diminished seventh, not a major seventh. That’s why this chord is not a major triad (which uses two major thirds), not an augmented triad (which uses two major third steps up to an augmented fifth), and not a minor seventh chord (which would have a minor seventh above the root rather than a diminished seventh).