The Dominant Seventh

As I’ve been hinting at a bit, the dominant seventh chord presents a particular challenge to what we might call the pentatonic method.  Here we see the problem illustrated by C7.  The strong tones E (the major third) and Bb (the minor seventh) are a tritone apart.  We know that these are so far apart on the circle of fifths that there is no pentatonic scale that will cover them both.  The choice we’re left with is to play Bb pentatonic (more suitable for C7sus4, as discussed above) or C pentatonic, which works but doesn’t have the dominant 7th quality because it doesn’t have the Bb. 

The blues scales have the tritone of the root in them, so maybe they offer salvation.  Bb and E blues both contain the Bb-e tritone.  Bb blues obviously is not a great choice, with the excluded Db and Eb.  E blues (G bluesy) is closer: e g a Bb b d.  The only problem is the excluded b natural.   So that’s one solution to play over C7: play the E blues and leave out the perfect fifth, b natural.  C9 (by which I mean here C7 with the ninth, D, added) presents the same challenge as C7.

This is the solution for the IV7 chord in many blues riffs.  Many blues riff are based on the bluesy scale, because they may form a major key accompaniment that will contrast with the blues scale (minor pentatonic) vocals or lead.  Often when played over the I7 chord these riffs include a crush note, which is typically the minor third as a grace note that resolves to the major third [todo: example].   In C, this means sliding from Eb to e over the chord C7.   Blues riffs may typically be repeated over the other chords in the progression without transposing, but often with minor alterations.   When playing the riff over the IV7 chord (F7 in the key of C), you don’t play the major third -- instead of crushing Eb to e you stay on Eb, which is of course the 7th of the F7.  If you did play the major third, the e, over F, you’d make an Fmaj7, which doesn’t really sound good against the F7.  So don’t.

The difference in attitude between “crush note” and “grace note” naturally leads to a difference in performance.  Make it rude - it’s often a percussive device.  Use just one finger when going from a black key to a white key.

If we’re going to be allowed to play the game of modifying scales, we could also modify the C pentatonic to substitute the minor seventh for the sixth: c d e g Bb.  I’ve heard this called the dominant pentatonic.  These are the notes of the C9 chord, so it makes sense.  You might also add the Bb to C pentatonic, making a six note scale that works well over dominant chords.

When the context is blues, the minor third isn’t necessarily excluded.  So C blues works over this chord (treating it as the I7) as does F blues (treating the C7 as V7) and G blues (treating the C7 as IV7).

To summarize, we have a few choices for soloing with pentatonics over C7, each of which has a drawback.   C pentatonic is safe, but doesn’t emphasize the seventh.  You can add the seventh (Bb) to make it work, but now you have a new six note scale.   Bb pentatonic works, but has the fourth f instead of the major third e.  A different five note scale, the dominant pentatonic, results when you substitute the e for the f in Bb pentatonic (which is the same as substituting the Bb for the a in C pentatonic), essentially adding 2 to the C7 to play the notes of C9.  E blues (aka G bluesy) works OK if you remember to not play the B.  In a blues context, the blues scales C, F and G might work, and you may consider the function of the chord in the key in deciding between them.

The usual jazz advice for dominant sevenths (at least the unaltered ones we’ve been considering) is to improvise in Mixolydian mode.  This means treat the chord as a V7: play C mixolydian (aka F major) over C7.  From the circle diagram you can see how this scale (seven notes starting at Bb) covers all the notes in the chord, and none of the excluded notes, so is a pretty good solution.  The circle of fifths diagrams should also work nicely for major scales and their modes, but I won’t explore that further here.

I’ll summarize the scales to play over each chord type in a table toward the end. For now, let’s turn our attention to the chords we can make out of the notes in the pentatonic scale.

Next: Chords of the Pentatonic