Why is this not "Tapadh leat a athair " since I'm speaking to a specific father?
Leibh isn't just for groups - it's used to address elder people and those of authority
i said 'a athair' can someone tell me why I am wrong?
If the noun begins with a vowel, it doesn't need an extra 'a' before it in the vocative case (I think).
You are correct.
wouldn't you use the more respectful leibh instead of leat with your father?
Depends. Some would, some wouldn't. There are different attitudes to this.
Yes, you are correct.
Can't you say tapadh leat
You absolutely can, but as the others comment mention, you would typically use leibh with your parents :)
seen what I was looking for below: that Gaidhlig loses the vocative participle before a vowel, although, I could have sworn that I have seen written so in Gaidhlig and heard it when living on the Uists. I could be wrong, no big deal.
The tips do say it used to be written, so you'll sometimes see it. And maybe it's a dialectic variant on the Uists.
Why does this not get "tha"?