Originally Posted by: xpayxphonexWhy does for example Min pentonic and other min scales work over a maj chord, and a maj scale doesn't work over a min chord.

At the risk of repeating something already posted (I have not read the entire thread), I'll put my 2c in.

Let's use the A minor pentatonic scale and the A major chord for example.

The A major chord has the notes A, C# and E, which are the 1 (root), 3rd, and 5th.

The A minor pentatonic scale has the notes A, C, D, E, G, which are the 1, b3, 4, 5 and b7 notes.

When you play these notes over the A chord, it works because it sounds "bluesy" to your ears. Your ears kinda' fill in the blanks and no longer hear the A chord as just a plain A major triad, but as a dominant chord, in this case an A7 chord, which has the notes A, C#, E and G, which are the 1, 3, 5 and b7 notes.

Hey, what about that C note in the A minor pentatonic? That still doesn't match.

Correct, but nearly a hundred years of jazzy/bluesy lines in popular music has our ears very used to hearing "extensions" and "alterations" of notes when played with Dominant 7th chords. Your ear hears the C note as a #9 altered extension of the chord.

The same is not true when playing a straight A major scale over the A minor chord. The b3, in this case the note C, is what makes the chord minor. You can play all the other notes in the A major scale over that A minor chord, but if you play that C# note, it absolutely looses any chance of sounding "minor" to your ear.

This all depends on the context of what other chords are being played, what the bass line is, etc. For instance, you can probably play some kinda' chromatic sequence including the C note, something like C, C#, D, A over the Aminor chord and make it sound cool, but then you are no longer playing a straight, plain ole' A major scale.

Peace,
Rico