Start with a G bar chord (3rd fret) Overlay or envision a
G maj pentatonic and a G min pentatonic, together. (guitar fretboard view) You'll note that what arises is a modified G dorian mode with a #4 or #11, depending on your view. If one plays a F maj scale or a major scale from the 7th of G or any chord (or whole step below root), the same result occurs. Raising the 5th of any major scale gives you a backdoor harmonic minor. (dorian #11) Lowering the 3rd of any major scale gives you a backdoor melodic minor. If you ignore the rule of melodic minor, it's really a jazz melodic minor. (dorian b9)
I believe it's monumentally difficult to memorized modal scales by rote. Knowing only major scales (pentatonic scales help in terms of visualizing on guitar),knowing the two ways to alter a major scale shortens the learning time, incredibly. Most jazz players go after tensions, rather than modes. If you are after a modal sound for modal sound sake, one must follow a previous post. My system gives you an infinite amount improvisational possiblities very quickly.
If you are a pentatonic player, fuse the major and minor
pentatonic together. Even adding the blue note (b5). Learn them cold. They are modified major scales with the view of the above paragraph. Next learn major scales and then, within the system I propose. Learn them cold. Then learn the two ways to alter. This helps to go or get away from verifying root. This system will go after what makes the particular chord or tonal center you are playing over tick.
Hope this helps.
A lie goes around the world before the truth gets it's shoes on. (Mark Twain)