Quote Originally Posted by jimc8p
Pentatonic scale is the most natural set of notes - a stack of fifths that blend freely with one another. Stack another fifth and you have a dissonant Major Seventh..stack another and you have a dissonant Augmented Fourth (the regular seven note scales have two half-step tensions and a tritone)... so I imagine that the major pentatonic would have been the easiest scale form to stumble upon pre-music.

The reason it sounds so good is because of its consonance. You cannot go wrong harmonically with a pentatonic scale. Its simple, large steps are pleasing and predictable. This is perhaps why it works so well in a dissonant bluesy setting with clashing thirds.

One thing I've always wondered - if you take any major scale, the 5 excluded notes from the chromatic scale make up a minor pentatonic from the Minor Third or a major pentatonic from the Augmented Fourth...most visually obvious as the distinction between white and black keys on a piano. Is this coincidence or the product of some obvious pattern? It seems like it must be obvious but I really cant think how this pattern works! ..any ideas?
It's just a pattern. Patterns don't have to mean anything...

It's the major pent of the tritone from the tonic, if that helps. (Opposite in the circle of 5ths.)
IOW, C major pent on the white notes, F#/Gb major pent on the black. The remaining notes (F/E# and B/Cb) are the semitones that complete the respective "opposite" major scales. (Or A minor pent and D#/Eb minor pent if you want the minors.)

IOW, it's not coincidence, but it's not particularly a highly revealing secret either. It's a natural result of the major scale structure.
(You might as well say it's "coincidence" that the C-F tetrachord of the major scale has the same structure as the G-C tetrachord... That's the way it's designed, because that's the way it works.)