half diminished chords

How the m7b5 chord fits in. Half diminished chords explained. How to use the half diminished chord. Minor 2 5 1 progressions.

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Video script:
To understand the naming of the half diminished seventh chord, remember that the word 'diminished' is used in music to mean something like 'even more minor than minor'.

Let's take you on a bit of a music theory journey. If we start with the formula for a major triad - 1 3 5 meaning it uses the 1st, 3rd and 5th notes of the major scale.

You change a major triad to a minor by flatting the 3rd. Then to get the diminished triad you flat the 5th as well.

A similar process occurs four-note chords. If we start with the first four-note chord most of us typically encounter - the dominant 7th - this has the formula 1 3 5 b7 - so it's just a major triad with a flat 7th note added to turn that into a minor 7th, unsurprising perhaps we just flatten the 3rd.

if we then flatten the 5th we arrive at a chord that is commonly called the m7b5, but is also known as our half diminished 7th chord - it's only a half-diminished 7th because the 7th interval used is a minor 7th. Only when we flatten the 7th again - in keeping with the concept 'even more minor than minor' - do we arrive at the diminished 7th which has the formula 1 b3 b5 bb7

Now if all that sounded like ancient Greek to you, then you may need to backtrack and study up on the basics of music theory.

A good grasp of music theory is needed for this next bit as well...
Having hopefully shed some light on the curious naming of this chord, now let's start looking at how it is used. And to best understand this we need to revisit the subject of harmonising scales. Starting as usual with the nice friendly C major scale.

If we harmonise this scale by piling three more notes vertically above each scale note in thirds - we arrive at the diatonic series of seventh chords for that scale. Notice that when we do this, the chord that naturally occurs built on the 7th egree of the scale is the Half Diminished chord. Also, notice that this is the only point in the scale this chord type occurs.

Now, in actual usage, we very rarely work with the 7th chord in a major key - functionally, it is almost always replaced by the dominant 5th for reasons we'll go into in another lesson. But for now, I want you to look closely at what happens when we take this diatonic series of chords in a major key, across into its relative minor key.
You may remember we do this by building the progression with the sixth step of the Major scale as our new key note - in this case that is A. So here we have the diatonic series of Am harmonised on the Natural minor scale. And you can see that our half-diminished chord is now the second chord in this key.

This means that it is the first chord used in a Minor 2 5 1 sequence. The 2 5 1 sequence is at the heart of most jazz compositions and a great many other musical compositions from other genres as well.

We have run quite a few lessons on the major 2 5 1 but in studying the m7b5 or half dim chord we can now look at how that is commonly used as the first chord in the Minor 2 5 1 so there I am simply playing the chords 2 5 1 from the diatonic series built on the natural minor scale, but more commonly, we hear this sequence based on the Harmonic minor scale, which means that it is strengthened somewhat by using a dominant 7th for the fifth instead of the rather weak, in terms of tension, minor 7th chord.

You may remember our 2 5 1 testbed from an earlier sound bite. Well we can use this to practice various ways of fingering the minor 2 5 1 like this. And once you have understood how the half diminished chord fits in with the concept of the minor 2 5 1 you will begin to see it used in this context in song after song. It is actually extremely rare, in my experience to see it used in any other way.

So, although we have had to cover some complicated ground to get here - this chord is actually one that is quite easy to understand and to work with and hope you have found this explanation has shed some light on that.

In the next lesson we'll look at a few approaches to improvising over the half-diminished chord.