Greg, I know this shit is a pain in the arse if people are just chucking terms, like key, mode and interval around without explaining anything. So I've recorded something over one of my tracks that you've heard before.
This is a two chord sequence. C/F follwed by Am - just repeated. So, I've decided that I want my lead to sound "cheery" so I've gone for the C Major (Inonian) scale. But, the C Major Scale is the same as the A Minor (Aeolian - think of it like your pentatonic) scale. So, in this case, I can use both the C Major scale with the the root note on the 8th Fret of the E String or the A Minor scale with root note on the 5th fret of the E String.
Now because of the way the C Major (Inonian) and A Minor (Aeolian) Scale fit with the chord sequence it sounds a bit Cheery (which I normally loathe) when I am playing C/F followed by a bit more Lonely when I am playing A Minor.
Remember these two scales are just "shapes" on the fretboard, the notes are identical (they're the same scale extended up the fretboard!). This means that you now have the freedom of movement to play anywhere within these two scale shapes and still sound in tune so now you have a pretty good reach over the fretboard, wherever your hand happens to be between these two chords. There is however a gap between the two scales so you can't move between them fluidly - but there's another scale shape to fill in the gap.
The order of your modal shapes is Inonian, Dorian, Phyrygian, Lydian, Mixolydian, Aeolian, Locrian. So the scale shape between Aeolian (which you're playing at A Minor) and Inonian (which you're playing at C Major) is a B Locrian.
Remember, your lead isn't going to be flipping between keys of A, B and C here - its all the same scale which is either C Major or A Minor depending on what way your brain in wired.
In the attached clip I run though the A Aeolian scale rooting on the 5th Fret (which sounds cheesey as fuck over the C chord, 'cos it implies a C major feel) then I go to a B Locrian scale (which is the same fucking notes) but now it sounds completely different 'cos I'm playing over A Minor so it has that kind of lonely feel to it. Then I play a C Ionian scale shape over the C. After that I just start adlibbing across all three scale shapes.
I feel that, when I go back to playing the C Inonian scale shape over the C chord, it still has a minory, lonely kind of feel to me. 'cos that's kind of what has got stuck in my brain now - one of those annoying cunts who says "have a nice day" when then serve you coffee might think differently
Have a listen
View attachment Scale Examples.mp3