Diminished chords are interesting creatures. They are known as symmetric chords because the interval between each chord tone is the same – a minor 3rd. There are also 2 tri-tone intervals. One between the 1st and 5th, and the other between the 3rd and 7th. We talked about the tri-tone’s distinct sound in dominant 7th chords, so you might think of a diminished chord kind of like a dom7 on steriods. It definitely is an energized, restless chord that is often used to move from one chord to the next. It is fair to say that dim7 chords and dom7 chords have a lot in common. They have similar sound quality, and are often used in the same way. In fact, a dom7(b9) chord, which you see all the time, can be played as a dim7, and I tend to think of them that way. You can see this if you take a G7(b9) and play the 3rd and 7th in your left hand and the 5th and b9 in your right. Now play an Abdim7 in an open position with the root and 5th in the bottom and the 7th and 3rd in the top. Exactly the same shape for both. See example below:

The symmetry of dim7 chords is a big help because there are actually only 3 chord structures to learn. An Fdim7 contains exactly the same notes as an Abdim7, a Bdim7 and a Ddim7. An F#dim7 can also be used to play an Adim7, a Cdim7, and an Ebdim7. Is that cool or what! Take some time, if needed, to acquaint yourself with this most useful concept.

When you’re voicing dim7 chords a great way to begin is to borrow the voicing idea that was covered in the dom7 section. That is, put a tri-tone interval in your left hand and put available tensions and/or remaining chord tones in your right. This will instantly give you a nice open voicing with room for colorful tensions. Instant hipness!

Next we need to pin down what scale(s) can be used to expand the note choices for dim7 chords. Dim7 chords come with their own special chord scale, created just for them. It’s called, as you might expect, a diminished scale, and it is very different from all the chord scales we’ve looked at so far. I can hear someone say “Arrgh! More scales to learn!” The dim7 symmetric structure will come to the rescue again. There are only 3 of these funny scales to learn. Here they are:

Notice that these scales have 8 notes instead of the usual 7. They are constructed of alternating whole and half step intervals. You can also say they are constructed of 2 minor tetrachords, each a tri-tone apart. Look at the first scale. The first 4 notes make up a C minor scale, and the 2nd 4 notes make up a Gb minor scale.

The first scale applies to Cdim7, Ebdim7, Gbdim7, and Adim7. The second scale applies to the C#dim7, Edim7, Gdim7, and Bbdim7. The last scale works for Ddim7, Fdim7, Abdim7, and Bdim7. Next we need to decide what are the best notes in these scales to add to our dim7 chords as available tensions. There are three that I find work well nearly all the time – the 9th, the 11th, and oddly, the 7th. It is interesting that the maj 7th is not a chord tone as you’d expect, but an available tension. This is just another example of the unique quality of dim7 chords.

Dim7 chords are often used to pass smoothly from one chord to the next. You’ll find examples of this in standard tunes all the time. Get out your fake book and take a look “Night and Day”, “Isn’t it Romantic”, or “Out of Nowhere”. You should find dim7 chords used in this way in each of these tunes. Another popular way to use the dim7 is as an approach, or substitute for a maj7 chord. Let’s say you have a Gmaj7 chord at the beginning of the tune. The pianist or guitarist will sometimes play a Gdim7 for 2 beats and resolve it to a Gmaj7 for the final 2 beats. It creates a very dramatic effect. You probably don’t want to use this re-harmonization technique all the time, but it is a cool trick to use to add drama and excitement to a performance. Here’s an example of voicings using passing dim7. The chords come from the opening of “Easy Living”:

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See how the shape and direction of the chords follows the top mallet, which is playing a little sequence going up in 3rds. Both open and close voicings are used to give variety to the sound. Using only open or only close voicings gets dull real quick. Mix it up. The next example is taken from the ending of Billy Strayhorn’s tune “Upper Manhhattan Medical Group”. The progression is simply a Dbdim7 resolving to a Dbmaj7, an interesting way to use diminished chords.

This time the dim7 chords have some tensions in the top voice. As always, analyze the notes and pay special attention to the top voice. It is moving down in 3rds this time, and the remaining 3 notes fill out the sound and support the top note. Compare the last chord in this example with the last chord in the previous example. In both cases the major 7 chords are all voiced using perfect 4th intervals. This sound is very distinctive and frequently used for both maj7 and min7 chords. I use them a lot because they sound great.

Since dim7 and dom7 chords have a lot in common you might want to practice them together. You want to get very good at picking out those tri-tones. Practice voicing dim7 chords in open positions like 1,5,7, 3. See if you can find the inversions – 5, 3, 1, 7 and 3, 7, 5, 1. Then try some 3 part chords with a tri-tone in the left and a tension in the right, just as you did with dom7 chords. Concentrate on seeing the similarities in these 2 chord types. There are many.

This concludes Lesson 2 and the analysis of  major, minor, dominant, and diminished chords. A truckload of information has been covered here. Don’t be impatient to move on to Lesson 3. You don’t need to master everything in a lesson before moving on to the next, but don’t race through them either. Each lesson builds on the last. In Lesson 3, the final in this course, you’ll be given chord progressions with the top note of each chord included. Your job will be to provide the remaining 2 or 3 notes to fill out the voicings. The goal will be to strengthen this “top-down” approach to comping. There will also be exercises to help you quickly identify common tones between any 2 chords. Identifying and using these common notes is a sure fire way to develop smooth voicing leading technique. Good luck!

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