"Is ea" or "Is é" ?
I've always been confused which to use in the copula. Could someone please give a explanation on which to use for asking a question and for giving the positive/negative answer or statement.
also how do you pronounce "is ea"? is it sa?
It depends on what you're asking. If you're asking a question that involved a definite noun, such as an é an dochtúir é you would answer with is and the correct pronoun. So here it'd be is é. This is often pronounced as if it were sé. Another example: an tú an múinteoir? The answer would be is mé.
If you do an indefinite one, such as an lacha e, then you use is ea, pronounced sea
You don't use either of them for asking a question - you use "an" for questions.
Perhaps you could post some sample statements that you think might use "is ea" or "is é", and that might highlight the confusion, rather than having other people post stuff that seems obvious to them, but might still be confusing to you.
"is ea" is pronounced "ih-sha", or just "sha".
"ea" is always right next to the copula - "an ea", "is ea", "ní hea", "nach ea" and "ba ea" always occur together, so you wouldn't put a noun between them. So "An buachaill é?", and the answer can be "Is ea" or "Ní hea"
"Is ea" doesn't have to be the answer to a question - you can say "Is buachaill é" or "Buachaill is ea é", with the second form being more emphatic in some cases.
Here are some examples from the NEID of "is ea" being used this way:
"I'm a vegetarian" - "is feoilséantóir mé", "feoilséantóir is ea mé"
"'Are you an expert?' 'I am.'" - "'An saineolaí thú?' 'Is ea.'"
"fatigue is characteristic of this illness" - "comhartha sóirt den tinneas seo is ea an tuirse"
"the mountain is a bare perpendicular rock" - "carraig lom cheartingearach is ea an sliabh"
"the picture is a representation of a tree" - "léiriú ar chrann is ea an pictiúr"
"it's a very graceful dance" - "damhsa an-ghrástúil is ea é"
(Note that "is ea" and "é" are used together in this last example).
"An ea" is what you might call a "confirmatory question". It's usually translated as "is it?", but there can be better translations depending on the context.
For example, the sarcastic "moi" example in the NEID:
"Boastful? Moi?" - "Gaisciúil? Mise, an ea?" (I don't think that you can really call that "béarlachas", but I'm not sure that it's a translation that Dineen or even De Bhaldraithe would have come up with)
In this example, "an ea" is "are you?":
"you're not from round here, are you?" - "ní ón áit seo thú, an ea?"
and in this example, "nach ea" might be understood as "are we not", though "isn't it" makes sense too:
"are we in Ireland or not?" - "an in Éirinn atáimid nó nach ea?"