What is a Diminished 7th Chord? – Part 1

You’ve no doubt heard diminished 7th chords before. Anytime you hear spooky chords in an old horror movie or a Liszt Hungarian Rhapsody, works of Richard Wagner, as well as many other pieces of music, they are pervasive. They serve very important functions. But what are diminished 7th chords?

If you aren’t familiar with music theory or if you haven’t watched my past video: Explaining Musical Intervals – Whole Steps and Half Steps, I would suggest starting there. As a refresher, a half step is two keys together with no keys between and a whole step is two keys together with one key between. If this sounds confusing it would be a good idea to watch the video linked above.

A diminished 7th chord is built on minor thirds, so it’s one-half step bigger than a whole step (a step and a half, or 3 half-steps). Just as there is only one Chromatic scale and two Whole Tone scales, there are only three possible diminished 7th chords. After that, they are all just inversions – starting on different notes of the same chord.

When you build a diminished 7th chord you start with a note and count 3 half-steps to each successive note. After building 4 notes this way, if you build one more you will be back to your starting note! You will soon discover that unlike all other 7th chords, you can’t really invert a diminished 7th chord – it would still be a diminished 7th chord – all minor 3rds. So there are only three possible diminished 7th chords.

The great thing is that diminished 7th chords can go almost anywhere. They are incredibly useful in modulating to other keys and they can be used in improvisation as well. Next week we will be going much more in-depth with these chords and explaining practical uses for them.

Thanks again for joining me, Robert Estrin Robert@LivingPianos.com.