Watch the Dom7 Chords online guitar lesson by Matthieu Brandt from Chord Cookbook

The chord we can build on the 7th degree of an Ionian Major scale is an unstable chord. This is due to the fact that the distance between the root and the fifth of the chord is 6 half notes. For major and minor chords this distance is a perfect fifth; 7 half notes. The 7th degree chord is called a diminished chord in a three note version and a half diminished seventh chord (m7b5) in a four note version. The most common use of this chord is on the second degree chord in a IIm7b5-V7-Im7, where the I chord is minor. In part two we'll take a look at altered 5th chords.