Originally Posted by: equatorIf the song is in the key of "C" you can play other scales than the obvious.
for example you can play:
A minor Pentatonic. [A,C,D,E,G]
D minor Pentatonic. [D,F,G,A,C]
G Pentatonic......... [G,A,B,C,D]
The reason you can play these scales is because they contain the notes of the "C major scale"

I know that, but the notes you would emphasize would still (given the same chord progression) likely be the strong notes (I V etc) of C Major, thus it would still technically be a Cmajor scale. Other scales you could play include G Major (Given a few interesting chromatic chords or a brief modulation) and actually just about EVERY major or minor scale out there, assuming you made the appropriate chromatic modulations. In fact, you could play in C# major if you really wanted to and were clever about it. But because this guy seemed so confused as to what a key was vs. a scale, I think we may want to stay pretty basic. To reitterate, if a song is in the key of C that means it is based (diatonically) around the C major scale. If a key is in Dminor it means that it is based (diatonically) off the D minor scale.

If you want to think of patterns, then yes, you could also (in C for example) play the Am patterns or the D Dorian patterns or the E phrygian patterns and what-have-you, but you'd be sure to emphasize the notes in C major that require emphasis, and thus wouldn't really be playing these relative scales at all. But it does help, sometimes, to think of the patterns.