#1
Hi there,

Very often you see online guitar teachers saying that when soloing over a twelve bar blues variation you should use te major pentatonic (or the major mixolydian mode) to solo over the I's and then you can use the I's minor pentatonic to solo over the IV and the V's. Now I was wondering, why is that the case? Is it because the I's minor pentatonic has many notes in common with the IV's mixolydian mod hence soloing I minor pentatonic over the IV chord sounds good?
#2
Their terminology is grossly misleading.

Blues harmony is based on dominant seventh chords. Written without the sevenths:
I | | | |
IV | | I | |
V | IV | I | |

Minor pent gives a 7#9 kind of sound, an extension of the dominant 7th sound. Major with the flattened seventh (colloquially called mixolydian) by definition fits the dominant 7th sound.
Between I and IV, the C minor pent shares notes with both (C as C7#9, F as F7).

Other people can expand.
#3
Quote by Knackworst1
Hi there,

Very often you see online guitar teachers saying that when soloing over a twelve bar blues variation you should use te major pentatonic (or the major mixolydian mode) to solo over the I's and then you can use the I's minor pentatonic to solo over the IV and the V's. Now I was wondering, why is that the case? Is it because the I's minor pentatonic has many notes in common with the IV's mixolydian mod hence soloing I minor pentatonic over the IV chord sounds good?
That would be why they'd suggest such an approach, yes. But it's still way too prescriptive and simplistic.

Blues is really the sound of a flexible minor pentatonic scale, in a dialogue with three major key triads. Thinking of different scales on each chord is a kind of "jazz theory" attitude, and is not how blues really works.
Sometimes blues players just stick to the minor pent of the key, regardless of the clashes.
Sometimes they bend the minor pent this way and that to resolve to the nearest chord tones.
Other times - a more "jazz" approach" - they abandon the minor pent and go for the major pent or mixolydian mode of each chord (but will probably still approach each major 3rd from the b3 below.).
Yet other times, all three methods might be combined in the same tune.

So there's no one "correct" way of playing blues. The second way is the most common. There's no reason to play the third way, unless you're playing something like piano where you can't bend notes (or unless you're reading some jazz chord-scale theory book). We're guitarists! We can bend notes!
#4
I tend to think that the I Minor Pentatonic is the overall structure for Blues, but with significant changes. Sometimes, I'll use mixolydian ideas, but still minor pent is the overall structure (BTW diminished arpeggios can also work really well!). As the previous poster mentioned "flexible" pentatonic minor with emphasis on flexible.

What you might want to do is compare the Minor Pentatonic with the chord tones. Notice where the additional notes are. Those are all absolutely great notes to hit (harmonically speaking) when that chord plays.

I suggested in another thread: just hear the progression in your head and practice trying to make the progression easily apparent to anyone who's listening to you solo. If you can do that, you're really playing with the changes and you're gtg after that -- so to speak.
#6
Scales are kinda of a backwards way to approach the blues. Blues is significantly about chord tones and blue notes. Chords tones are self explanatory. Blue notes are the b3 and b5 of the triad.

Scales are things you'll draw on for melody, but the idea isn't to play a scale or mode. The point of blues soloing is to push and pull against the chords.

There's also a lot to be said for articulation. Vibrato, bends, slides, and such are a huge part of effective blue soloing.
#7
A common device is to use the Dorian scale (rather, Dorian licks) over a non-tonic chord of the moment, (That is, in major key, over ii, IV, V (and vii)). The Dorian is rooted where ii is found in relation to that chord.

In blues, the 7 chord of the moment is often thought of as a V chord (hence implies where ii can be found). The interval from ii to V is 5 semitones (e.g from the root of Dm to the root of G7). The ii is 5 semitones lower, or equivalently 7 semitones higher (i.e. the same pitch class, but an octave higher) than the V root.

Hence, in blues in C, could use G Dorian against C7, C Dorian against F7 and D Dorian against G7. Dorian contains minor pentatonic.

By just playing the minor triad from the Dorian root, this has the effect of making the original 7 chord sound like a 9th. (e.g G min with C7)