A diminished seventh chord in closed position has different four notes, each of which is separated from the other by a distance of three semitones. Having said that, it should be clarified that a semitone is the smallest distance between two notes on a piano and closed position involves the different notes of a chord being placed as closely as possible to each other. Here are three different diminished chords:

B, D, F and Ab

B#, D#, F# and A

C#, E, G and Bb

Practically speaking, all other diminished seventh chords are derived from the above. For example, D, F, Ab and Cb would have been the next diminished chord in the above list, had I continued with a fourth example. However, D, F, Ab and Cb contain the same notes as B, D, F and Ab (the first chord in the list above). The only difference is the order in which the notes appear and the spelling of one of the notes (i.e. B and Cb are the same note on a piano).

So why state a comprehensive listing of twelve diminished seventh chords below. It is precisely because of the spelling of the notes that we have the more comprehensive list. The ways that notes are spelled out indicate which key we are in during a composition. From a theoretical standpoint, this knowledge is invaluable. Here is a more comprehensive listing of twelve different diminished seventh chords (all spelled differently):

B, D, F and Ab

B#, D#, F# and A

C#, E, G and Bb

D, F, Ab and Cb

D#, F#, A and C

E, G, Bb and Db

E#, G#, B and D

F#, A, C and Eb

Fx, A#, C# and E

G#, B, D and F

A, C, Eb and Gb

A#, C#, E and G

Examples one through twelve above belong to the following minor keys respectively: C, C#, D, Eb, E, F, F#, G, G#, A, Bb and B. As a composer, knowing what key you are writing in is a necessity. As a pianist, the more insight you have into a composition that you are performing, the more depth you can give to your interpretation.

Here is a fascinating observation involving diminished seventh chords. If you take, for example, a diminished seventh chord of C minor (B, D, F and Ab), you can create four different dominant seventh chords by simply lowering any one of the notes in the chord by a semitone (a half step).

As a demonstration, if we lower the top note as such: B, D, F and G, then we have a dominant seventh chord of C major and a potential modulation to the tonic major of your original key. In plain English, that means that we can easily change keys from C minor to C major.

Using this system, the diminished seventh opens up the possibility of four different, quick modulations, making this chord a powerful tool in the hands of a skilled composer or piano improviser.