Curious about Cs
So I am curious about the use of Cs in Irish Trad! Recently I played a tune at our session but was surprised to find that they use C sharp not C natural. (They said that the tune is played both ways…my version, learned from an Irish group on YouTube, uses C natural). And I played along with an old video of an Irish fiddler, and noticed his Cs are neither C-sharp or C-natural, but something “in-between”?
Is this just part of the looser aural tradition, where they could see where someone’s finger is landing, but can’t see exactly where? Or is there a deep traditional history behind these “variable” Cs?