What are diminished chords?

Diminished chords are very cool, and easy to understand. Diminished chords serve a cadential function just like a dominant 7. Let’s look at a dominant 7 chord construction in the key of C:

In the key of c the dominant chord would be a G

Chord tones: G B D

T make it a dominant 7 add the F:

Chord Tones: G B D F

Now let’s look at the diminished chord in the key of C which would be a B Diminished:

Chord tones: B D F

To make it a diminished 7 or a minor 7b5 which is how it is most commonly referred to add the a

Chord tones: B D F A

Now if you look closely at the two chords

G7: G B D F

Bm7b5: B D F A

The only thing separating these two notes is the A and the G, so they can be used interchangeably to perform the same function.

There are in reality two types of diminished chords The Half diminished which is the minor7b5: B D F A. And, there is also the full diminished chord: B D F Ab

Here is a form for each of the diminished chords.

   ------ ------ ------ ------
   ---3-- ---3-- ---1-- ---1--
   ---2-- ---1-- ---2-- ---2--
   ---3-- ---3-- ---2-- ---1--
   ---2-- ---2-- ------ ------
   ------ ------ ---2-- ---2--

Just like all bar chords these are universal shapes and can be moved anywhere on the fretboard and you will come out with a diminished chord as long as the shape is retained.

One of my favorite tunes that utilizes the diminished chord is Autumn Leaves. Check out the lesson Jazz Comping V for an arrangement of Autumn Leaves. You should probably get yourself a Jazz real book and go from there.

Well, I hope I have been helpful, please feel free to email me with any questions.