This guitar lesson is a quick tour through different modal harmonic contexts, so that you can hear how the pentatonic scale sounds when used as a substitution for a 7 note scale or mode.
For each example I play the Original Mode, then the Parallel Pentatonic Scale and then the Parallel Blues Scale. I am using the exact pentatonic fingering, in the same position, with the same guitar sound, so that you can focus more on how harmonic context affects the sound.
Listen to how switching from the original mode to the pentatonic scale changes the character of the music, but also how the sound of the same pentatonic scale is colored each time by each different harmonic context.
Historically, the pentatonic scale was actually developed in many cultures before the appearance of 7 note scales, but in terms of modern harmony, we consider it a subset of a 7 note scale. Take a look at this chart to understand what I mean.
In the same way, a Major Pentatonic is missing degrees 4 and 7, so it can be used as a substitution for these 4 modes*:
* Lydian Dominant is the 4th mode of Melodic Minor
Keep in mind that these are not the only contexts where pentatonics can be used. Using the process of harmonic simplification, they can be used in blues and minor blues, over most harmonic minor progressions, or for the more harmonically adventurous, as upper structure substitutions over many different harmonies.