Originally Posted by: Mglambo

Hello Christopher Schlegel ...[/quote]

Hey, back at you. :)

Originally Posted by: Mglambo

Was jamming to a backing track. It was D chords and E chords. So I played some lead in A major thinking that was the key.[/quote][p]Good thinking. A major is the only key that has both those major chords. The big clue there would be 2 major chords a whole step apart, that's got to be the IV & V chords from A major.

[quote=Mglambo]It sounded pretty good. Then I fooled around in D and then in E with varying success. I wrote down all the common notes in these 3 keys and the only notes not in any of the three were A#, C, and F.

Close!

Key of A major: a - b - c# - d - e - f# - g#

Key of D major: d - e - f# - g - a - b - c#

Key of E major: e - f# - g# - a - b - c# - d#

So, there are a lot of notes in common: a - b - c# - e - f#. This is the A major pentatonic scale!

But notice that if you play the E major scale while the E major chord is happening it can sound fine, too. Likewise with the D major scale while the D major chord is happening. Which notes sound okay depend on what is happening overall with the music at that time.

The big lesson here is that context is everything.

If you play the notes of the A major scale while another guitarist is hammering away on an A major chord or a bass player is playing an A note in eighth notes, then the combined effect is going to sound like a strong, happy major scale starting on the root.

If you play the notes of the A major scale while another guitarist is hammering away on a D major chord or a bass player is playing a D note in eighth notes, then the combined effect is going to be that peculiar half spacey, half fantasy sound of the Lydian mode of starting on the 4th scale degree.

If you play the notes of the A major scale while another guitarist is hammering away on an E major chord or a bass player is playing an E note in eighth notes, then the combined effect is going to be the bluesy, pop-rock sound of the mixolydian mode starting on the 5th scale degree.

Consider another option!

If you play the notes of the A major scale while another guitarist is hammering away on an F# minor chord or a bass player is playing an F# note in eighth notes, then the combined effect is going to be the sad or serious sound of the minor mode or scale because you are essentially playing A major's relative minor scale.

Context is everything.

[quote=Mglambo]So if I avoided those 3 notes it sounded decent. Same with key of C...if I avoided C#, D#, and G# it sounded ok. This may be a backwards way of looking at modes? but does this make any sense?

Yes, it makes sense! You find a group of notes that sound good. And if it sounds good to you then you use it & look for why. Usually the reason is that the notes you like are part of some key or mode related system.

This leads to another important point about scales & soloing: you don't have to use every note in the scale. You are supposed to use the scale as a palette of options, not a laundry list of ingredients that must be included. Use the scale or modes as a list of possibilities, then target chord tones, then build melodic phrases.

Hope this helps! Please ask more if necessary & have fun experimenting with improv!