The mixolydian mode has a flat-seven and the harmonic association with the dominant 7th chord. We can think about the dominant 7th chord in a couple of ways. Let’s use G7 as our example. G7 has pitches G-B-D-F. This collection of notes can be looked at as a G major triad, G-B-D, with an added minor seventh note, F. The chord can also be viewed as two over-lapping triads having two notes in common; G major, G-B-D, and B diminished, B-D-F. We can also look at the chord in terms of stacked major and minor thirds; major-minor-minor, in its root position.
Now that we understand the underlying harmony, let’s dig a little further into the mode. First we will look at the relative relationship to the tonic. A given key will have a tonic-dominant relationship. We can think about the tonic note or chord as home and the dominant note and chord as the element or force that wants to push us back to home. In this way mixolydian is associated dominant chord having the tension that wants to take us to the tonic. If we chose the fifth note of a major key and spell out the notes from there, we will spell out the mixolydian mode. In the key of C, for example, we would start on pitch G.
The mixolydian mode does not always function exactly in this way though. For example, a dominant 7th chord may be used as a tonic chord, as is often the case in blues progressions. Furthermore, the chord can be found anywhere within a tonality. In this way let’s focus a little more on the mixolydian mode as it relates to the dominant 7th chord.
We know that the dominant seventh chord or arpeggio spells out four of the seven notes of the mixolydian mode, G-B-D-F. Those tones are the Root, third, fifth, and flat seven. So what about the other three notes? Again, let’s use G mixolydian as an example and find out. These notes are G-A-B-C-D-E-F-(G). So A, C, and E are the three notes we are looking for because G, B, D, F are the notes from the chord. Pitch A, is the nine, C is the eleven, and E is the thirteen. We can stack thirds G-B-D-F-A-C-E or Root, three, five, flat seven, nine, eleven, and thirteen. These notes are the tensions within the harmony.
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