In the last tetrachord lesson we went over the concept of tetrachords and how they change the way we think about scale patterns. In that lesson the focus was the major modes and a question was posted asking about the melodic minor and harmonic minor modes. Therefore this week’s article will go over tetrachords in the melodic minor and how those also apply to the harmonic minor. To re-cap a tetrachord is a collection of four scalar-adjacent tones. Two tetrachords combined create the standard eight-tone scale.
Let’s start off with the melodic minor tetrachords. The melodic minor scale differs from the major scale by having a flat third. In classical theory a distinction is drawn between the ascending and descending melodic minor scales, but for our purposes we’re only going to use one scale. The melodic minor scale uses many of the same tetrachord forms as the major scale though they are combined in different ways. We still have the Minor Tetrachord which has the whole-half-whole step relationship between notes, the Major Tetrachord with the whole-whole-half step layout, the Phrygian Tetrachord with the half-whole-whole step relationship and the Lydian Tetrachord with the whole-whole-whole step relationship. The patterns for all of these tetrachords were covered in the previous lesson.
There is one additional tetrachord form which we must add: the Diminished Tetrachord. The diminished tetrachord has a pattern of half-whole-half. In the key of C-melodic minor the diminished tetrachord can be found in the relationship from B to Eb.
The associated tabs are:
Now that we have the tetrachords defined we can combine them to create the melodic minor modes. The modes in melodic minor work the same way as they do in the major forms. Each mode corresponds to playing within the key on a different starting tone. For example, C-melodic minor mode 1 would be the standard C-melodic minor scale. C-melodic minor mode 2 would be the Bb melodic minor scale played from C to C (since C is the second note in B melodic minor) and so on. Here are the tetrachord combinations do give the different melodic minor modes:
The harmonic minor mode introduces yet another tetrachord form – the Extended Tetrachord. It has a pattern of half-whole+half-half. In C-harmonic minor this is the relationship between the notes from G to C (the upper half of the scale).
The associated tabs are as follows:
The harmonic minor scale is a combination of the minor tetrachord and this extended tetrachord. As an exercise try to figure out the other tetrachord combinations for the rest of the harmonic minor modes.
In case you missed last week the best way to practice these tetrachord combinations is to run through the different fret pattern sequences. For example if I’m working on the melodic minor patterns and want to make sure I understand all the possible fret-pattern combinations my practice session may look like the following:
This is a small sample of what you would practice – ideally you would run all the patterns in all combinations for all the different modes. This would let you gain the most complete understanding of the fretboard patterns. The goal is develop the muscle-memory vocabulary in your fingers so that you can quickly modulate between the modes and scales. Breaking the scales down into tetrachords gives you twice the flexibility, knowing the different patterns gives you the agility. Good luck practicing!