Modes!!!

Hi Andy,apart from the regular major and minor scales (which originated as modes also), there are modes, like dorian, phrygian, lydian etc. Modes are scales that were discovered by the ancient Greeks, but often revived throughout music history. See an online encyclopedia for more technical info. A good way to get to know the modes is to play a major scale of C, starting/ending on d (dorian) , e (phrygian), f (lydian), g (mixolydian), a (aeolian) b (locrian).
The reason for using modes is the atmosphere they create, if music is composed within one of the modes, because they bring their own sets of chords (to be found easily by stacking thirds on a root note of the mode, staying within diatonic order the mode concerned.
Hope this helps.

for me, modes are vital for walking and soloing. know your key center and go. No guess work or "wiggling your fingers"

I really pay very little attention to modes when it comes to playing music. Music is a sound not a name of a sound. I only use modes to describe a certain tonality to a piano player or guitar player who is comping or something like that. Because there are specific sounds compositionally that I go for I do ask, for instance, for a certain kind of minor chord to be dorian as opposed to aeolian when describing the sound of a passage of music to another musician. But I'm certainly never thinking about a mode or scale when I'm playing a solo, a bass line, or comping for someone. I'm thinking about melody.

Modes are useful for analysis, education, and explanation, and I would highly recommend having a good working knowledge of them if you want to communicate certain things to musicians verbally. But when it comes to playing music, me melodic, and try not to think about what it actually is that you're playing.

Easy,

Janek