the words for "his", "her" and "their" *look* the same, but there is a difference in the mutations they cause on the following word: a chat = his cat a cat = her cat a gcat = their cat a athair = his father a hathair = her father a n-athair = their father As you can see, "a" lenites a following consonant when it means "he", it does nothing to consonants, but prefixes an "h" to vowels when it means "her", and it eclipses when it means "their". The other possessive pronouns are: mo (+lenition) = my, becomes m' before vowels or fh do (+lenition) = your (singular), becomes d' before vowels or fh ár (+ eclipsis) = our bhur (+eclipsis) = your (plural)

Well, that didn't work out how I'd hoped; I'll inbox you.

An easier way to remember it in your head (and the way it was taught to me) is to have them grouped together and in order, like so: mo - my ár - our do - your bhur - your (pl) a - his a - their a - her (You see the left column of pronouns causes Lenition; the right column causes Eclipsis.) cat (cat) mo chat ár gcat do chat bhur gcat a chat a gcat a cat athair (father) m'athair ár n-athair d'athair bhur n-athair a athair a n-athair a hathair