I'm trying to figure out how I can mix major and minor pentatonic scales and was wondering if someone could explain the underlying theory concepts that would dictate under what chords/chord changes does a switch sound good and also from which notes can you use to go from minor to major or major to minor. What I mean by the latter is, are there doorway notes, like the root, that can be used to switch in between scales and if so what are they?
First it's important to understand when it is appropriate to mix minor and major pentatonic scales. If you have a piece in minor you will want to stick to a minor (pentatonic) scale. If you have a piece in major which is not meant to sound bluesy, you want to stick to a major (pentatonic) scale. You only want to mix the two in a blues context, i.e. either in a blues song, or in a piece where you want certain parts to sound a bit bluesy.
Blues is all about mixing notes from the major and the minor scales. An exception is the minor blues, where you don't want any notes from the major scale. In a piece based on major or dominant chords (all with a major third), the minor scale notes are perceived as bluesy ("blue notes"). In addition, there's the b5, which is also referred to as blue note, and which is neither part of the minor nor the major pentatonic scale (it is part of the blues scale; that's the difference between a pentatonic scale and a blues scale).
I'll give you an example of how to mix the notes from the major and minor pentatonic scales over the chords of a standard blues: I7, IV7, V7. Note that all scales have the root of the I7 chord, so e.g. for a blues in C, the scales I refer to are the C major and the C minor pentatonic scales. (Note that it is possible to use scales with the roots of the IV and V chords, but that's a different subject).
- I7: both minor and major pentatonic work fine
- IV7: minor pentatonic is OK, major pentatonic has to be used carefully because of the major third (in C: E), which clashes with the b7 of the IV7 chord (in C: the note Eb in F7)
- V7: both minor and major pentatonic work fine
As pointed out by Tim, it is a common trick to use the major pentatonic scale over the I7 chord, and then switch to the minor pentatonic over the IV7 chord. One way to find nice ways to mix the two is to localize all chromatic parts of the combined scale, and use those to move between the two scales, e.g. in the key of C from Bb to A, from E to Eb, or starting on the F (F,E,Eb), or upwards D,Eb,E, or chromatic approach of the note E (works over I7): D,F,D,Eb,E, etc.
Note that after a while you will not so much think of it in terms of switching between minor and major, but you will hear the chord tones and add those tones to your basic scale, which could be the blues scale. The result is similar, but you will be able to choose the notes in a more musical way.
The best way to learn how to do it is to analyze players who basically use all 12 notes to play over a blues. Note that you don't have to go into jazz to find that. As a guitar player, I'd suggest you listen to Robben Ford and Larry Carlton. I often work on exactly that topic with my students by analyzing Larry Carlton's solo on "The B.P. Blues":
First, let's establish what those notes are. C maj pent. contains C, D, E, G and A. C min pent. has C, Eb, F, G and Bb. So, the common notes are G and funnily enough, C. C, being the root of each, is pivotal, as is the perfect fifth, G. Playing over a C major accompaniment, Eb will hardly sound diatonic, which is why it often gets bent up at least a little, paying lip service to the major 3rd, E.
Rather than switch, a lot of players think along the lines of "I have a pool of C, D, Eb, E, F, G, A and Bb", actually only leaving out 4 other notes from the chromatic 12, which could still actually be used at some points in a piece. So there is no absolute necessity to think 'now I'm using maj pent/ min pent'.
If you want, in a piece in C, say, you could work with that idea, and it would sound 'nice' with maj pent, and a little more edgy with min pent. But, there's another way. This all works perfectly when the song is ON C, but when it changes to be ON F, for example, a slightly different set of pents comes into play, literally. So, let's say you use an E for the last bit on C, that could slide down to Eb for the start of the F bar. Now, you've gone from maj pent. (C) to min pent. (F).
Maybe to simplify this, consider the notes constituting C maj pent. and G maj pent. As above, C, D, E, G and A for C. G will have G, A, B, D and E. So the common notes are D, E, G and A. Thus, to move from C chord to G chord for a solo, these four could link as tied or repeated note quite happily. Food for thought...
I would add something that may very well be controversial. I do believe the only difference between the minor pentatonic and the Major pentatonic is the notes they start on and that they are pretty much the same scale.
a minor Pentatonic has the same notes as C Major Pentatonic so you could easily move between the two.