Yeah my problem with learning Gaelic was that I was much more interested in seeing the linguistic patterns in the sound changes (m -> w is a form of denasalization as well as lenition) than in remembering *when* that happened :) Although the question of 'when' is also a linguistic one, just a bit more arbitrary than the regularity of how the sounds change.

So I just looked it up because I wanted to remember. (None of this will be news to you, I'm just sort of thinking out loud here and explaining where my confusion came from)

The initial consonant of Irish nouns will often become lenited when the case changes (nominative -> genitive for example giving m->w) and this also happens in many other environments as well.

But in other environments, you get what's called eclipsis instead. Here, b -> mb, d -> nd, and g -> ng (this is what I was remembering as nasalization). You also get 'n' before vowel-initial words. p, c, and t don't get nasalized, but instead get voiced: p -> bp, c -> gc, t -> dt.

The fact that [b,d,g] act one way and [p,t,c] act another way *makes perfect sense* to a linguist. So that's the sort of thing that fascinated me, and I never paid enough attention to *when* these changes happened :)

I do wish I had had more time to learn Gaelic though. Knowing more languages is good for a linguist.