i'm new to this forum, be gentle. i come from a jazz background in music , guitar mainly but also a little trumpet.

with folk music, it seems as all the tunes r harmonically simple, you can really play whatever you like.. isn't that the point? you arrange it to suit your style? for example... over a G major based melody.. e.g notes-

G A B C D E F#

You can play secondary harmony (e.g m7, MAJ7, DOM7, b7#5) if approached in the right way..look at Bellowhead, or that collaboration that never made it- Paraellagram

yes..if your in a folk session,playing these chords may not work with what other people are playing, but if you do play these chords while another guitarist plays other chords then your an idiot... the point of a 'session' is to LISTEN to other players.. interact etc etc.. not stop playing because someone else is, or play like everyone else to the lowest common denominator..LISTEN, JAM, INTEREACT and just PLAY!