Is it possible to say "Cá bhfuil a cás?" ('Where is her case?") or "Cá bhfuil a chás?" ("Where is his case?")?
Could I get a view of the rules for lenitation for her and his?. does 'a' (her/his) sometimes lenitate, sometimes not?
When 'a' means 'his' it lenites.
When 'a' means 'her' it does not lenite.
The lenition lesson mentions this at the beginning in its "tips and notes" section.
does this rule change when the noun starts with a vowel a hathair - her father a hostan - her hotel both been given as answers in previous parts of the course.
No, prefixing a h is not lenition, it's Irish's third mutation known as pre-aspiration.
a = his, lenites.
a = her, pre-aspirates.
a = their, eclipses.
Although lenition is indicated in writing with a 'h', this doesn't really relate to the pronunciation. 'dh' is a completely different letter to d.
The pre-aspiration cased by 'a = her' however is a genuine h sound being added to the word.
Surely most of the options offered would have been correct. DL may have had something in mind, but "a chás" is as valid as "a cásanna"
I see what you mean. You mean when the sentence comes with the drop down menu to fill in the last blank. I just looked at the six solutions, and every single one would be grammatically correct, but would require different meanings of "a." But without a translation provided, there's no way to know if Duo wants to have it mean "his", "her" or "their." I sent an error report, and make sure you do, too.