Originally Posted by: yoobeeCan the "key" be chosen from any string or only from the low "E" string ?

The musical key that you play in is the major or minor scale in which the song, section or melody is based. The scale from which most of the notes in the music you are playing belong.

The key can be chosen from any of the 12 available musical alphabet letters:

A, B-flat, B, C, D-flat, D, E-flat, E, F, G-flat, G, A-flat.

Any melody or song can be played starting in any key you desire; any one of those 12 letters. You can find those notes on any string of the guitar, not just the low E string. You pick a letter, apply a scale (major or minor), then find it on the instrument!

Other factors would include, which key works best for the tune, if it going to be sung by a singer with a certain range, what instrument it will be played on (flat keys typically work well for brass instruments, natural keys for guitar).

Hope that helps.