A friend of mine has started writing a lot of songs and has asked me to play bass on them. His songs are very indie-poppish and have mainly chords with no melody (no singer yet) so the space is very open for bass playing. My problem is that I'm having trouble determining the key center when he sends me the chord charts (he doesn't include the key) and I'm having even more trouble determining the tones to use behind the chord progressions. Where I'm confused is whether or not I just use the tones of the chord (i.e. the triads) or is the scale pre-determined by the progression? For instance one of the progressions is: Gtr run Fmaj7 Cmaj7 gtr run Fmaj7 Cmaj7 Dmin7 Cmaj7 Emin7 Dmin7 the guitar run is A,D,E,G I know, a lot of 7's but it sounds better than it looks, but my question is whether or not I have to play the tones only within each chord? Or is there an extended scale to which I could play underneath this entire progression? I can't even tell what key this progression is in. My knowledge of theory is very limited. I've studied modes in the past but I didn't get past learning them individually. I guess this would probably be the lesson where you put them together to play over a progression..... hahaha.... well any help is welcomed. Books, vids, practice recommendations, anything, I've been struggling with this for a while and i'm ready to get over it. Thanks in advance.