Irish traditional music has traditionally been learned by ear.
In the tradition, written collection have usually been viewed as irrelevant, more or less. Not evil, just irrelevant.
Most written collections of Irish traditional music suffer from one of the following problems:
-
They’re written by people who have a firm command of standard music notation, but aren’t steeped in the tradition.
-
They’re written by people steeped in the tradition, but don’t know much about music notation.
It becomes a self-fulfilling thing, resulting in poorly notated tunes that don’t do anybody much of a service.
Traditional players, if they use notation at all, usually use ABC notation rather than ordinary staff notation.
Richard is summing up the accepted narrative there.
Reality is, as it usually is, a bit more nuanced and less absolute. Many musicians did have writing skills and compiled collections of music or exchanged tunes in written form. Staff notation was used, tonic solfa was common at one time as were simple systems like ABC (not the internet ABC you see on these forums) or number systems like Padraig O’Keeffe used (O’Keeffe is a wellknown example but many others used self devised systems). Others depended fully on their ear for new tunes and their memory to retain them.
I don’t know about written collections being considered irrelevant. Musicians have always been keen to learn new tunes, in any available manner, and written/printed collections have always been part of transmission. There are well worn stories of local groups of musicians meeting to learn tunes from O’Neill’s collection with a musical literate of the company playing through the book. Overall the rapid spread of tunes published in O’Neill’s book or the first volumes of Ceol Rinnce na hEirreann in their time tells you all you need to know about the the esteem these publications were held in.
It’s sort of interesting that in an area like East Galway musicians ‘ran out of tunes to learn’ after they had collectively gone through O’Neill’s and then decided to take turns composing a new tune for the group to learn. I do not recall if these new tunes were submitted in written form though.
I have met musicians over time seem to that fit Richard’s description, ear players but I have also known the other side of the coin, people maintaining collections of written music. One of them was piper/fiddler/whistler Martin Rochford who would pursue you if he heard a tune he liked but didn’t know, until you had written it down for him. And he in turn would pass these tunes on in written form. I once mentioned this to Bill Ochs, who in response told me how during the seventies he was visiting a mutual friend, Ronnie Wathen, who was at that time based in Feakle in east Clare. One night Bill played a tune he had learned from a Boys of the Lough recording ‘The Killarney Boys of Pleasure’. Martin knocked on the door the next day in search of the tune and didn’t leave until Bill had committed it to paper. It’s been a solid part of the east Clare repertoire for decades now.

Martin Rochford playing the fiddle during the early 90s. On that occasion I wrote a reel, a, John Brosnan composition, for him that he heard me play earlier.
I remember taking a photograph of Peter O’Loughlin once, with discussions like this in mind, while he was playing through a manuscript collection on the back of his car, parked in the street in Feakle. I can’t find that immediately I am afraid.
I have also on occasion heard older musicians refer to Scottish tune collections that were going around, ‘that one I found in Kerr’s book’ , that sort of thing.
Anyhow, my point is that there are no absolutes one way or the other. Irish music is simple and easily picked up by ear once you’re familiar with the idiom and thus that would be the common manner of picking up tunes. But musicians will learn tunes wherever they find them, by ear, from other musicians radio or recordings, but they won’t shy away fro mother means and written music is part of the process of transmission as well