kenny wrote:
Why would a "whistle and fiddle player" who is "advanced" need "music theory" if you've managed to get to "advanced" without it ?
I can think of a few reasons.
First, the word "mixolydian" is fun to say. Mixolydian. Mixolydian.
Second, it helps with chords. Many of our "minor" tunes are really dorian, with its very common minor-major pattern E.g. Em-D-Em-D, and knowing that sort of thing helps me find my way around a tune. If your instrument doesn't play chords, it can also help with counterpoint or alternate notes.
Third, it helps with sets. One of our sessioneers is a real stickler for pairing up tunes with a good solid contrast. A bit of theory helps a great deal when someone wants to raid their memory banks for a tune with a contrasting key or mode.
Meanwhile, I'm a big fan of pairing up tunes that reinforce a certain mood (rollicking+rollicking, cerebral+cerebral, melancholy+melancholy.) Music theory doesn't help so much with that, but it does help me dig up matching tunes that will also satisfy my buddy's sense of contrast.
Fourth, it does give some insight into the character of Irish music. ITM made much more sense to me once I learned how tunes often have chord progressions that oscillate one note up or down. For Dorian and Mixolydian (Mixolydian. Mixolydian.) tunes this is natural and widespread, e.g. The Pigeon on the Gate, or the High Reel. For major tunes, it's still common for Irish tunes to step up and down, and in fact it's almost stereotypical, e.g. The Irish Washerwoman or The New Copperplate. Noticing that has made it easier for me to hear tunes, and to learn them by ear.
Finally, although ITM is not so formal, knowing some formalism helps you to combat other formalism. For example, once in a while someone will find some sheet music (bleh) that is clearly mistaken, e.g. a key signature mistakenly set to Gmaj because one of the Cs is natural. It helps to be able to say, look, that must be mistaken because it makes no sense for the other Cs to be natural with the chord progression of the tune.
I'm sure I can think of some other reasons. It helped when a fiddler came by and played Liz Carroll's slip jig for Rose and Kathleen, and I noticed it actually followed a blues progression. Sometimes that stuff is just below the surface and it helps to see it.