Half-diminished 7th chords are very important.
Not only do they naturally occur on the 7th tone of any major scale, they are used as great preparers for dominant chords on the 5th tone.
If you play gospel, you’ve undoubtedly used a half-diminished 7th chord on the 2nd tone of the scale to lead to the 5th.
Half-Diminished 7th Chord Basics
By going to the 7th tone of any scale and playing every other note, you’ll form the half-diminished 7th chord.
For example, in C major, the 7th tone is B.
Simply play B + D + F + A (every other note of C major scale) and you’ve got yourself a B half-diminished 7th chord.
Other Alternatives to Forming Half-Diminished 7th Chords
The first three notes of a half-diminished 7th chord in root position look identical to the diminished triad. For example, in the chord above (B half-diminished 7th), if you take off the last note, you’re left with B + D + F, which is a B diminished triad.
And diminished chords are formed by simply stacking a bunch of minor third intervals together.
Note: Minor thirds have three half steps between them.
B to D is minor third.
D to F is minor third.
Where the “half-diminished 7th” chord differs is in the last interval. Instead of another minor third like the B diminished 7th chord (B + D + F + Ab), you play a major third, which is four half steps.
F to Ab is minor third.
F to A is major third. <---- This is the one you choose the differentiate the half-diminished 7th from a typical diminished 7th chord.
Compare the two: Half-diminished 7th vs diminished 7th
B diminished 7th
B half-diminished 7th
It’s all in the last interval… and the difference in one tiny half step.
We’ll talk about where to use the half-diminished 7th chord tomorrow.