I'm familiar with diatonic modes,scale degree, and building chords and I'm familiar with Major and Minor Pentatonic. My understanding for better or worse is that a pentatonic scale doesn't function as a tonal center.
Is pentatonic improvisation within a tonal center as simple as just staying within underlying modal structure as a subset of the notes? I know someone can always add notes outside for effect.
I'll grab a look at that book. I don't want to absorb too much of your time.
A maj or min (both types) pentatonic scale could be used to establish a tonal centre of sorts if the music stayed firmly within just those 5 notes, but they're usually not used exactly like that.
In cultures where the indigenous music is totally based on pentatonic scales and where there is little or no use of the entire diatonic scale then to the extent that this music exhibits the feeling of a tonal centre I think we'd have to say that tonal centre WAS a function of the usage of that scale. No?
In jazz and popular music the most common ways that pentatonic scales are used for melody or improvisation are on chords in which all 5-notes of the pentatonic scale do not create any "avoid notes" on the chord-of-the-moment.
Examples, from the C major scale:
On Cmaj7, as Imaj7 in the key of C, it is common to use the C maj pent and the G maj pent scales.
C is the root, D is the 9th (an "available extension"), E is the 3rd, G is the 5th and A is the 13th (another available extension on this chord).
Both these pentatonics can be seen as subsets of the C maj scale.
The other pentatonic that exists within the C maj scale pitch collection is the F maj pent scale.
But the note F, if emphasised on Cmaj7, creates a rub (an "avoid note") with the chord's 3rd, E, which is usually voiced below the F, creating a b9 interval or a b2. E-F
So F maj pent is usually not an appropriate choice over Cmaj7 unless you're trying create some sort of unsettled dissonant effect.
Implicit in the above is that every major scale contains 3 maj pentatonic scales within it.
There's a pent on I IV and V.
Lots of guitar players coming from rock tend to see these as min pentatonic scales (the 1st type I mentioned earlier) on II, III and VI.
E.g. C maj pent = A min pent
F maj pent = Dmin pent
G maj pent = E min pent
On Dm7, as IIm7 in the key of C major, it is common to use F maj pent, C maj pent and G maj pent.
Those scales are arranged in order of most Dm7-ish to least Dm7-ish.
I.e. The F maj pent scale, aka the D min pent scale can be thought of as an arpeggio of Dm7(add4).
The other two pent scales have fewer chord tones and more extensions.
On Em7, as IIIm7 in the key of C major, the only maj pent scale scale that can be derived from the C maj scale that doesn't contain any avoid notes is the G maj pent aka E min pent.
But this chord is often functioning as Cmaj9/E so it's not uncommon to apply the C maj pent on this too even though the C note creates a rub with the B in the chord below.
But the note F is pretty harsh on this chord if emphasised.
On Fmaj7, as IVmaj7 in the key of C, all 3 maj pent scales work.
The order of in-to-out is the same as the order of the pents on Dm7.
Note that using G maj pent on Fmaj7 brings in the note B which is a #11 on Fmaj7, the characteristic note of the lydian scale.
It's fairly common these days to apply a lydian scale colour on Imaj7 chords too so another option on Cmaj7 in this key is to use the D maj pent scale even though it brings in a note, F#, that is foreign to the key.
On G7, as V7, the usual suspect is just G maj pent because the note C tends to create a rub with the chord's 3rd, B.
But if the chord is G7sus4 all 3 maj pents will sound strong.
B-C is a b9 or a b2 which is quite dissonant.
But if the C is below the B, as it would be in a G7sus4 with a B played above it as a melody note, the interval is C-B is a maj 7th which is much less dissonant.
On G7sus4 the extension B is usually enumerated/labeled as "add10" (or sometimes "add17" believe it or not).
E.g. "G7sus4(10)" or "G7sus4(addB)", etc.
On Am7, as VIm7 in C, the usual suspects are C maj pent, aka A min pent and G maj pent.
F maj pent doesn't work so well because F is an avoid note on this chord since it clashes with the chord's 5th, E.
On Bm7b5, as VIIm7b5 in C, the only maj pent from the C scale that doesn't contain the avoid note, C, is the G maj pent.
One real easy thing to take away from this is that the min pent scale from the chord's root will work on ANY min chord you ever have to play over and the maj pent scale from the chord's root will work on most maj chords you ever encounter.
Getting familiar with then idea that on most maj7 chords a maj pent from the chord's 5th is usually a cool sound is a good idea too.
The harmonic minor scale and its modes do not contain any maj pentatonic scales.
The mel min scale has a maj pent on its 5th degree. E.g. C mel min contains all the notes of F maj pent.
But the other really common way that pentatonic scales are used in jazz and popular music is in the blues.
I.e. It's quite common to use A min pent aka C maj pent on a blues progression that is in the key of A major rather than A minor.
And in this application you will see avoid notes being employed more or less with abandon.
Although this is a really common sound that everybody knows how to play it's actually sort of tricky to justify theoretically and brings in all sorts of concepts like modal interchange and bi-tonality.
I don't have time to get into that today.
Hope that helps.