"He is funny, isn't he?"
Translation:Tá sé greannmhar, nach bhfuil sé?
Tá sé greannmhar, an ea?
When the sentence was, "She's a good woman, isn't she?" an ea was acceptable for Isn't she. In this sentence, though, an ea was marked wrong. They said I should have used "nach bhfuil sé." Is this a case of "I can use it, but you can't", or is there a real reason that it cannot be used in this case?
greannmhar is an an adjective, not a noun, so you say Tá sé greannmhar, not is greannmhar é.
To use the copula, you'd have to attach the adjective to a noun - is fear greannmhar é, and then your tag question would have to change so that it also used the copula - nach ea.