Playing Am pentatonic scale over A blues chord progression

Question

I had a guitar entrance exam yesterday regarding improvisation. The guy put on a A blues backing track and told me to improvise. As I'm not a blues guy myself, I went and improvised on the A major scale (Ionian mode). After a few seconds he stopped me and asked me if I was playing on the pentatonic, I said no and that I'm currently playing on the Ionian mode. He told me that the pentatonic is more appropriate to blues and to play on it. I said ok and proceeded to play on the F# minor pentatonic scale, since its A major's relative minor. He stopped me again and told me to play the A minor pentatonic scale, saying that's what gives it the blues feel- playing the minor scale on a major chord progression (Am pentatonic on A blues chord progression). He failed me at the test (even tho my improv wasn't anything close to bad).

Note: this was not a 'blues improvisation exam', but simply an improvisation exam.

Now my question; was my 'mistake' that serious? Yes, I'm not a blues guy and my improv was not so bluesy probably, but still, failing me felt totally out of the blue.

Edit for clarification, since this came out more as a rant: Is it obvious and known that minor pentatonic should be played on major chord progression (Am pentatonic on top of A) in blues, and are other scales (pentatonic on relative minor/other modes) used as much in blues improvisation.

Answer 1

There are a variety of scales that can be used in blues improvisation, depending somewhat on the specific style involved. However, using a A minor pentatonic over an A blues is the most basic. It's a very typical first scale taught in blues improvisation, and it would be reasonably expected in an audition or examination that this would be known.

An A major blues contains three main chords: A7, D7, and E7. The A minor pentatonic — A C D E G — contains pitches common to those chords so provides a simple way to begin improvising. A slightly more advanced improviser might use the A minor pentatonic over the A7 chord, then switch to different scales for the D7 and E7.

There are also blues scales, mixolydian scales, and bebop scales, all of which are frequently used in blues (or jazz) improvisation.

Blues itself comes in many variations with many different chords and alterations to those chords, so there is a corresponding proliferation of scales that could be used.

Answer 2

It's common to use the minor pent. over a Blues, and most Blues will use major, or more likely dominant seventh chords throughout. Major pent. will work, but won't sound too bluesy. It'll sound fine over the tonic (I), but not work over IV or V so well. You moving to F♯m pent. gave you exactly the same set of notes,(as A major pent.) no wonder he stopped you again!

Your teacher should have warned you that minor pent. works over both major and minor Blues songs, but major pent. will not work over minor Blues.

The main notes that make something Blues are ♭3, ♭5 and ♭7, (the 1st and last of which occur in minor pent.); none of which you would be using with major pent. No wonder he stopped you. You should still have played a decent solo over the sequence, but it wouldn't have sounded too bluesy.

Blues players will usually mix major and minor pents. in their playing, adding bends to particular notes. These would be expected in someone asked to improvise over a Blues sequence. And probably there was none of that, as the notes you stuck to didn't allow that to happen. Or maybe you bent notes that shouldn't need bending?