Can we say "mo duine" - my husband
Can't we say "mo duine" = my husband Or should we always say = an duine agam ? If the later, why?
Always an duine agam.
First, if you wanted to use mo, you need lenition, so *mo dhuine (
mo duine is just plainly ungrammatical), but that doesn’t mean my husband. I am not a native (or even competent) speaker, so I cannot comment how that phrase sounds like to one, but I guess that it’d be a pretty weird way of saying my person.
And for my wife you’d say mo bhean (and not *an bhean agam). For both you could say mo chèile (my spouse). That’s just how those concepts are expressed in Gaelic.
I have no idea why the language settled on using alienable (an X agam) possession for husband, when for the rest of close family it uses the inaliebale (mo X) one.
So, what's considered inalienable in Gaelic? Blood relatives are, a wife (but not a husband!), clothes, children, parts of your body and certain special entities as kings, queens, and religious icons. A very nice illustrative example is the difference between mo làmh and an làmh agam. The first one talks about your hand that's attached to your body and therefore inalienable - but the second expression would suggest you're talking about a severed hand that you're holding in your own hand!!! Or, less macabre, seo an làmh agam might mean you're showing your hand in a game of cards - this is my hand (of cards).
(In Irish, though, there is no distinction between alienable/inalienable possession, and there my wife is mo bhean (chéile) and my husband is m’fhear (céile), while duine means only person).