The Blues Progression and the Blues Scale
The simple blues progression consists of three dominant 7th chords, I 7, IV 7 and V 7. The measure layout is as follows: I 7 (4 bars), IV 7 (2 bars), I 7 (2 bars), V 7 (1 bar), IV 7 (1 bar) and I 7 (2 bars). So blues in the key of C would be: C 7 (4 bars), F 7 (2 bars), C 7 (2 bars), G 7 (1 bar), F 7 (1 bar) and C 7 (2 bars). Before you try to improvise on the blues progression, you should first know the structure of the chords! The C7 includes the notes C, E, G, Bb (1, 3, 5, b7), the F 7 includes the notes F, A, C, Eb (1, 3, 5, b7) and the G7 includes the notes G, B, D, F (1, 3, 5, b7).
You can improvise on just the chord tones and that is a good place to start. It is always good to emphasize the 3rd and 7th of the chord because those tones identify what kind of chord it is! In this case the major 3rd and flat 7th reveal the dominant 7th sound! You can also improvise on dominant 7th or Mixolydian scales. They are simply major scales with flatted 7th tones like the dominant 7th chords. Remember that the 4th scale step is very dissonant against the 3rd of the chord and wants to move to the 3rd! Otherwise, any other notes in the scale will sound okay when emphasized. So, when a C Mixolydian scale is used with a C 7, C, D, E, G, A and Bb are all notes that may be emphasized. However, F must resolve to E! I call that the “amen” of jazz!
The Blues Scale
The Blues Scale is so-called because it includes notes that are considered “blue” notes, the lowered 3rd, lowered 5th and lowered 7th of the key. A Blues scale built on C has the following notes: C, Eb, F, F#, G and Bb (1, b3, 4, #4, 5 and b7). When used with a C 7, the Eb gives a “bluesy” sound to the chord. That is probably because Eb would be a minor 3rd in the chord and we generally seem to hear minor sounds as being sad or bluesy! However, you don’t normally have both a major 3rd and a minor 3rd in a chord so the Eb is really D#, the raised 9th of the chord! So we hear it as an alteration of the harmony. The same is true of F# which is the raised 11th of the chord. Bb, of course, is just the lowered 7th of the chord but it is not in the normal major key signature so it takes on a bluesy character!
Minor Blues scale of the key!
The beauty of the blues scale is that it generally fits all three chords in the blues progression. Unlike other chord progressions and their related scales or modes, you don’t use a separate scale for each chord. The blues scale built on the key center works with all three chords in the progression! However, you do have to be careful of certain notes that will sound dissonant or “wrong” on each of the chords.
Below you will see the blues scale in the key of C shown next to each chord with the “wrong” notes in parentheses.
C7 – C, Eb, (F), F#, G, Bb – F clashes with the 3rd, E
F7 – C, Eb, F, F#, G, (Bb) – Bb clashes with the 3rd. A
G7 – (C), Eb, F, (F#), G, Bb – C clashes with the 3rd, B and F# clashes with the 7th, F.
Since the blues scale has such a strong feeling of the key, we generally don’t worry about the clash of C against the 3rd of the V chord, G7. Melodic ideas moving through the scale may pass by those dissonant notes without a problem but they shouldn’t be emphasized against the chord! The best test is to play each chord on a keyboard, holding down the sustain pedal, and play the scale over it with your instrument (if you are a pianist, play and hold the chord with your left hand and play the blues scale with your right hand). Listen for which notes sound best with each chord! If you listen carefully, your ear will tell you which notes are a problem! At first improvise using only two or three notes of the blues scale and compose ideas that you like the sound of on each chord.
Major Blues Scale
Another mode of the blues scale may be used. I call it the Major Blues scale and, built on C, it contains the following notes: C, D, D#, E, G, and A (1, 2, #2, 3, 5, and 6. Since it contains both the major 3rd and the minor 3rd of the key, it is easy to emphasize important chord tones. On the C7, you could emphasize E and when the chord changes to F7, you could emphasize Eb (D#). All the other notes fit both chords. Another option is to use a separate Major Blues scale on each of the three chords. So, on the IV chord, F7, the notes would be F, G, G#, A, and D. The scale for G7 would be G, A, A#, B, D, and E. This would create the opportunity to use exact repetition of ideas on any of the three chords.
There are not just one or two blues scales. There are variations for major chords and some scales contain chromatic passing tones in different locations. There are many jazz cliches that use a form of the scale that adds a passing tone between 5 and 6. So this variation of the blues scale would look like this built on C7: C, D, D#, E, G, G#, A and C. One typical melodic idea might be : G, G#, A, C, D, A, C or Eb (D#), D, C, A, Ab (G#), G.
There are many variations on the chord progression of the blues. One of the most common forms uses a II-V-I progression in the last four bars. The blues scale may not sound as good over this progression. One solution is to play the major scale of the key over those three chords. Also, in the 8th measure, there is usually a VI7 chord to lead to the II chord in the next measure. This usually will sound best if it is altered by using either Harmonic Minor of the II chord or Melodic Minor a 1/2 step above the root of the II chord. So, on an A7, the scale would be D Harmonic Minor or Eb Melodic Minor.
Dominant 7th Scales
On any of the dominant 7th chords in a blues progression, there are a number of scales that may be used: Mixolydian, the Bebop scale, Lydian b7, and the Lydian Bebop scale. If you want more tension, you could use scales with alterations in them like Whole Tone, Diminished and Super Locrian. A handout on dominant 7th scales can be found on my web site, danhaerle.com.