Anyone who is into Blues music or Rock will most likely be very familiar with the sound of the Mixolydian Scale/Mode. However on it’s own the scale may need some help and encouragement to really develop to it’s full potential.
Much Blues Piano work which pioneered the Blues used the Mixolydian Scale. However in Blues piano it was important to follow the chord changes (particularly those of the IV chord and V chord) with changes to the Mixolydian appropriate to those chord changes. For example it was rare for a piece played in say the Key of A to stay solely on the A Mixolydian Scale throughout the entire piece over the most likely chord changes of IV ( D Maj) and V (E Maj). So in Key of A more normally you will encounter that the A Mixolydian changes to D Mixolydian over the IV chord and again may change to E Mixolydian over the V Chord. There is good reason for this as we can see if we examine the scale to find out it’s inherent weaknesses.
The Mixolydian is a great scale but it lacks some key ingredients to make it super useful for the Blues and Blues based music such as Rock. To address this many players have adapted an approach to using the scale and adapting the Scale to use in the Blues by amalgamating this scale with a parallel Minor scale such as a Pentatonic minor on the same Tonic note. Since we started with examples in A then we will continue to use A. So here I refer to scales of A minor pentatonic. This approach was common in players such as BB King’s style of playing for example.
Over a Dominant 7th progression typical of Blues the Mixolydian would be the scale of choice. So a Blues Progression in Key A the key chords would be A7 (the Root chord-Tonic), then the IV Chord the D7 , then the V Chord E7. These are the typical chords. Now you could play just the A Mixolydian Scale over all 3 chords in the progression but there would be some problems and you would need to show some caution particularly when playing this scale over the IV Chord D7. This is the reason why many players avoid playing the Root/tonic Major Scale over the IV chord. They either switch to play the Root/Tonic Minor scale at this point in the progression or they opt to follow with a switch to the major scale or major pentatonic of the IV chord. So in the case of a change from A7 to D7 they might switch to play in either A minor pentatonic, or D major or minor pentatonics over the D7 chord.
First let’s look at the Mixolydian Scale in A. the first thing to note is that the scale is a Major scale so should fit will over Major chords. The second thing to note is that the 7th note is always flattened ( bVii). For more details on scale construction refer to other sources because this is not covered here.
R ii iii- IV- V VI bVII R
If you played this scale over the D7 chord there would be a nasty clash & unpleasant discord of the C# note against the C natural note in D7 chord. So this must be avoided. Also when playing this scale against a V Chord E7 this scale prevents you from expressing the the 3rd of the chord because it doesn’t contain the G# note. This can be quite limiting.
Making a Hybrid Scale to fit better over the chords of the progression.
So it is obvious that using just this A Mixolydian Scale over a Progression of Dominant 7th chords can have it’s limitations using this approach. That is is why many players often combine the Mixolydian with a parallel minor scale. The minor scale will have a flattened 3rd note (bIII). In the case of A minor this will be C natural. This is the alternative approach to having to switch in another scale to play over the IV chord as detailed above. Essentially it lets you stay with one single scale to which you make adjustments in order to be fit against the chords that you are playing over.
This C note fits much better against the D7 chord which also has a C natural note. Also using the C natural (bIII) gives us the blue note when played against the Tonic Chord of A7 or A maj. Combining the Mixolydian and the minor Pentatonic gives us a Hybrid scale. This approach is found in the playing styles of BB King for example. It allows us to stay basically on one scale over the whole progression.
Hybrid Scale in A A-B-C-C#-D-E-F#-G-A bIII
Another method is to change the scale as the chords change
There is another method of using the Mixolydian against a progression of Dominant Seventh Chords and that is by following the progression with scale changes. So playing A Mixolydian over the A (I) chord, followed by the D Mixolydian scale over the D7 (IV) Chord and finally the E Mixolydian over the E7 (V) chord. this is a popular method in Blues Piano Styles. Coloured notes in the example scales show the note in the respective chords. The red coloured note is noteworthy because it has not been available by any of the previous methods detailed. This note is the III note of the V7 chord and helps establish a greater sense of detail about the chord. Many players add this note to minor pentatonic scales when playing over the V chord. Eric Clapton is known for this.
A Mixo A-B-C#-D-E-F#-G-A