Why is it that chord progressions which include the II or II7 chord (A or A7 in the key of G, for example) are common in Irish songs, but not in Irish instrumental music? I come from a bluegrass background where every other piece, whether song or instrumental, has an A7 in it in a minor or "passing chord" role. This convention does not seem to exist in Irish fiddle tunes. However, it seems that many of the Irish "sing-along" songs ("When Irish Eyes are Cryin'", for example)do use it.

I have made some idle speculations on this subject in the past, but will not go into them here for fear of sounding like an idiot. Any serious musicologists out there care to comment?