Does tidsear really change to thidseir in the vocative
tidsear = teacher; > thidseir in vocative? I don't mean the "h", I mean "sear" > "seir"...thanks, <sub>WH</sub>
The vocative puts "a" in front of the name unless it begins with a vowel (or, after lenition, with Fh followed by a vowel).
Then the name lenites by putting an h after the first letter if that letter is one which accepts lenition, and the letter T is one of these.
Then a masculine name or title also slenderises if possible, by either changing the last vowel (if it's broad) to an "i" or adding an "i" before the last consonant. "Tidsear" is a masculine title, so it does this.
So you end up with "a tidseir". Similarly "Seumas" changes to "a Sheumais" in the vocative.
There are probably other wee wrinkles I've forgotten about but this rule seems to cover most eventualities.
Oh, who knows why people do anything really! I think we pick up a bit at a time. I have got the vocative pretty much nailed, but there's a discussion around "sùilean brèagha" versus "sùil bhrèagha" that is doing my head in.
Also a' versus an t- and stuff like that. But that's what practice (and re-reading the tips) is for!