It's needed to link back to múinteoir. So, yes, you do need it for this construction, which emphasizes "teacher' (I.e. "He is a teacher).
I didn't understand. Why does it need emphasis and it's not correct without ea?
It doesn't need emphasis. You could as easily have said is múinteoir é. But as it stands above, it's an emphatic sentence and requires ea
but if I wrote "Is múinteoir é" it would mean "HE is a teacher" - is that correct?
Is múinteoir é means "He is a teacher". Múinteoir is ea é means "He is a teacher".
confusing this Canadian boy... what is the purpose of ea perhaps not just in this situation but generally? Ive not seen it yet,.. i dont think
It's not more a form of é than í is. It's a completely different pronoun used in certain cases, like when the predicate is not definite.
Thanks for following up. Also re-reading the teanglann site, "ea" is 3.rd person neuter, thus definitely neither é nor í
3 sg. neuter pron. (Used only in conjunction with the copula)
Is this pronounced 'iss,' as it is at the beginning of sentences, or 'ish,' like it is when is ea is shortened to 'sea?'
It's the same word, so by default pronounced 'iss'. But before é, ea, í, iad, it's 'ish'. https://en.wiktionary.org/wiki/is#Irish
As an add on: especially in rapid speech, the DeNTaLS DoTS consonants tend to change their broad/slender pronunciation to match the first letter of the next word. So is mise tends to be 'shmisha', while is túsa is 'stoosa' (the 'i' is often dropped, as acknowledged in writing for sea). Same for other words ending in a DeNTaLS DoTS. https://en.wikipedia.org/wiki/Irish_phonology#Sandhi
I dunno if this will help (it helped me), in Hib Eng;
'(it) is a teacher he (is)' - 'Is múinteoir é'
a teacher is he - Múinteoir is ea é.
Both are 'he is a teacher' in standard English but the second is slightly more empathetic.
I'm guessing 'HE is a teacher' wud be something like; 'Sése is ea múinteoir é.'? ( Is sése féin múinteoir atá ann?)