Scroll down to the bottom of this link http://www.bitesizeirishgaelic.com/blog/i-me-he-him/ for the emphatic forms of le+ pronoun.
In general, though, be prepared to see a -se (mise), -sa (tusa), etc (complete list:http://nualeargais.ie/gnag/person.htm) to put emphasis on a pronoun instead of saying the word more forcefully. The preposition + pronoun construction often has special forms, too, like liomsa and leatsa.
I think it's leatsa because of the implied contrast: i.e. it's yours (not mine / not hers / etc.). Think of the "tune" of an English sentence like "The lobster's mine but the crab's yours"; how it emphasizes the last word. This is done in Irish with the addition of an "emphatic particle", -sa.
I'd say that is leat is more likely to be used where the emphasis is more on the "what" than the "whose" -- especially in a list. The only example I can think of for the moment is from the Bible, Psalm 47: The day is thine, the night also is thine = Is leat an lá agus is leat an oíche.
This was such a wonderful explanation!!! Thank you for the link, Cait48!
That depends on the sentence. The sentence I see on the page is Is leatsa an portán In this case, bportán would not be possible, since the article an (the) doesn't change masculine nouns like portán. If you had a sentence where you wanted to say your crab--like Your crab is on the table, you could say do phortán (to one person) or bhur bportán (to two or more people).
An identificational copular statement with a third-person pronoun as the subject can’t have the copula directly adjacent to its complement; the first é is a “subcomplement” that provides that separation. Think of it as approximately “It’s that, your crab.”, with the first é corresponding (non-literally) to “that”.
I'm not a native speaker, and very far from becoming fluent - but, with due respect, I don't find the phrase awkward- you'll find the rhythm echoed in some dialects ( if that helps) - "it's your crab (so) it is" - " it's your crab, hey." I found this helped me a bit when trying to get my head round some of the constructions and how they might be varied.
Is é is commonly contracted to sé so you might hear Sé do phortán é.
There is an Irish song whose chorus begins Sé mo laoch mo ghile mear.
That is the normal structure for an identificational copular statement with a third-person pronoun as the subject, so that’s how I’d use it. I’m not a native Irish speaker, though, so you’ll need to find some to ask to find out if they’d shorten it — my guess is that a native speaker would probably pronounce it as ’Sé do phortán é.
It's an archaic second-person singular possessive--in other words, 'your.' In theory, 'thy' was used before consonants and 'thine' before vowels. Shakespeare wrote (in that famously misunderstood line from Hamlet), 'To thine own self be true.'
Where did this question come from? I find some of Duolingo's sentences unnatural, but not to the extent of using 'thine'!
Differently from what?
Portán is the basic form, the one you would find in a dictionary. Sometimes (like after mo and do) there is a séimhiú on the word, which is then spelled phortán. At other times (like after ár or bhur) there is an urú on the word, which is then spelled bportán.
I think that Is leatsa an portán might be better translated as "It's your crab" (cé leis é? Is liomsa é), with the emphasis on your, and I don't see how that would match "you have the crab",
On the other hand, if you had two people deciding which one of them would get a single crab - one party might concede with "you have the crab" or "the crab is yours", but I think that's really "you can have the crab".
le is a preposition. leatsa is a prepositional pronoun. The "preposition+an causes elipsis" construction doesn't work with prepositional pronouns.
Note that in the specific case of le, le + an becomes leis an, but that leis is NOT the prepositional pronoun leis (le+sé). So leis an bportán is preposition+an, not prepositional-pronoun+an.