Peter, It helps to understand modes, and the chords that can be structured from their scales when accompanying fiddle tunes. The most frequently used modes in fiddle music are the Aeolian, the Dorian, and the Myxolydian. In the Aeolian, or natural minor scale, for instance you would know that the I chord is minor, the IV chord is minor and the V7 chord is minor. In the Dorian mode, the I chord is minor, the IV chord is Major, and the V chord is minor, although more often the VII chord is used which is Major. In the Myxolydian mode, the I chord is Major, the IV chord is Major, the V chord is minor. Usually the VII chord is substituted for the V chord, the VII being Major. It may help to associate a well know fiddle tune with a particular mode, for example Old Joe Clark is a Myxolydian tune, so is June Apple. (Cold) Frosty Morning is a Dorian tune. Does this help?