The Diminished 7th Sound

Built upward, the diminished 7th is three stacked minor 3rds — 4 tones in all. In a drill it arrives in a key you did not choose, so the only thing left to listen to is that shape.

Near missesdiminished triad, half-diminished 7th and minor 6th chord — each one is this chord with a single tone moved, which is why a wrong answer here is almost never random.

It sits in the edge tier — the shapes whose difficulty is that they refuse to name a root.