"He is a positive boy."
Translation:Is buachaill dearfach é.
The first "é" is superfluous - it serves no grammatical purpose in this exercise.
The purpose of the first "é" in an exercise like "Is é an t-innealtóir é" (https://www.duolingo.com/comment/7657367) is to separate "is" from the definite predicate "an t-innealtóir". As "buachaill" doesn't have a definite article that "é" isn't necessary, and it has no place in this sentence.
Thanks for the response. Syntax of the copula is something that still confuses me, even though I've been learning Irish for quite a while now. If you wouldn't mind then perhaps you could check if my understanding is correct, as you seem to know what you're talking about!
So in a straightforward classification, the word order is simply copula-predicate-subject:
Is Sasanach mé (="I am an English person")
Is máthair í (="she is a mother")
Is foirgnimh iad (="they are buildings")
If the subject is a third person noun (including proper nouns), the pronoun is still included and the subject comes afterwards:
Is máthair í an bhean (="the woman is a mother")
Is máthair í Áine (="Áine is a mother")
Is foirgnimh iad bainc (="banks are buildings")
Is foirgneamh é seo (="this is a building")
If the predicate includes a definite article or a possessive, i.e., the subject is being identified as a specific person or thing rather than a general member of a group, the predicate can't be next to the copula. If the subject is a first or second person pronoun, it comes first and is (usually?) emphatic:
Is mise an Sasanach (="I am the English person")
Is tusa mo mháthair (="you are my mother")
If it's third person, the subject still comes before the predicate but there's also a kind of extra pronoun before the subject:
Is í ?Áine mo mháthair (="Áine is my mother")
Is í seo mo mháthair (="this is my mother")
Is í an bhean an mháthair (="the woman is the mother")
If it's third person and the subject is a pronoun, you end up with two object pronouns:
Is í mo mháthair í (="she is my mother")
Is é an Sasanach é (="he is the Englishman")
Is iad na foirgnimh iad (="they are the buildings")
So in this case, as you say, it would fall under the first category as there's no definite article. But variations with an 'extra' pronoun might include Is buachaill dearfach é Pól (="Paul is a positive boy"), Is é Pól an buachail dearfach (="Paul is the positive boy"), Is é an buachaill dearfach é (="he is the positive boy").
Is that all correct?
I'll be perfectly honest - I only rely on the "rules" when a copular construction doesn't "feel right", and that's simply a matter of exposure and practice. I only think about the "rules" for copular constructions as a last resort.
The one simplification that you might make to your set of rules is in the last one: "If it's third person and the subject is a pronoun, you end up with two object pronouns". If you consider the two sentences:
"Is Sasanach é" - "he is an Englishman"
"Is é an Sasanach é" - "he is the Englishman"
Rather than considering the first "é" in the second sentence as a second "object pronoun", it is simply a sub-predicate whose sole purpose is to separate the copula from the definite noun. (The same goes for "Is í Áine mo mháthair" - while the sub-predicate takes the form of a pronoun, there is no "she" in this sentence).
Of course, this is complicated somewhat by the situation n Ulster Irish, where the actual predicate has been dropped, and the sub-predicate is all that's left - "Is é an Sasanach".