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.