I am struggling to understand gender agreement and the copula and could really use some guidance. I will give some examples of what I have in mind:

The time-old example of asking for a number
Céard é d'uimhir ghutháin? --- céard é because... the answer could be anything?
Céard í uimhir do ghutháin? --- céard í because... the answer is definitely a number?
[the context for this last one being i donno a pile of numbered phones that are being distributed?]

Is é m'uimhir ghutháin ná #### --- so the é is agreeing with ####, right?
Is ##### í m'uimhir ghutháin --- so the í is agreeing with uimhir, right?
Is í m'uimhir ghutháin an t-aon rud a bhí uaidh --- are any of these even right??

Is tabhachtach í an fhilíocht
Is tabhachtach é filíocht a chumadh
Is tabhachtach í filíocht na hÉireann
Is tabhachtach é filíocht na hÉireann a léamh
Is tabhachtach an rud í an fhilíocht ??? are these right wrong?

Céard é príomhchathair na Rúise? -- asking is it a city? a town? a slum?
Céard í príomhchathair na Rúise? -- asking is it Moscow? Paris? Beijing?
Or rather is one right and the other impossible?

Is í an Róimh príomhchathair na hIodáile
Is é Moscó príomchathair na Rúise
Is príomhchathair na Rúise é Moscó

Is í mo mháthair an duine is tabhachtaí in Éirinn
Is é an duine is tabhachtaí in Éirinn ná mo mháthair --- ???
Is duine tabhachtach í mo mháthair


Sorry if this is too much but I am struggling with rules that I cannot find written anywhere and answers that always involve "it's just my intuition." The biggest struggle is with "céard" -- is the combination "céard í" even possible??

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Céard é, céard í, céard iad are all correct.

Which to use depends, of course, on the kind of question.
There are two kinds of questions:

A normal question.
Here you can use either é, í, iad depending on the gender and number of the following noun.
Céard í príomhchathair na Rúise?
Céard iad na príomhchathreacha san Eoraip?
etc.

And then there is the so-called pseudo-cleft question.
Here you can use only é, irrespective of the following noun (é is anticipating the answer)
Céard é do bharúil?

Which kind of question to use?
Well, it depends. Often both are possible, sometimes only a pseudo-cleft is correct.

So does that mean that all of the things I wrote are correct?
Even "Céard í d'uimhir ghutháin?" is possible?
Or when is it that only a pseudo-cleft question is correct?

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All things aren't correct. There are some minor mistakes, afaik (mistakes irrelative with your quesion, see below).
But I don't see why Céard í d’uimhir ghutháin? should be wrong.

A pseudo-cleft question is necessary if the answer is likely to be a pseudo-cleft.
e.g. Céard é do bharúil? because the answer is usually Is é mo bharúil go ...


I don't think a pronoun with verbal noun clauses is necessary at all.
Is tabhachtach filíocht a chumadh.
Is tabhachtach filíocht na hÉireann a léamh.

EDIT: It means something different with a pronoun:
Is tabhachtach é filíocht na hÉireann a léamh. - It's important that he should read Irish poetry


That is wrong.
Is í príomhchathair na Rúise Moscó.
or (better?):
Is é Moscó príomhchathair na Rúise.
You cannot combine the copula with a definite predicate without a helping pronoun (a sub-predicate).
A sub-subject on the other hand occurs only in sentences with an indefinite predicate,
e.g. Is príomhchathair é Moscó. (Moscow is a capital)

Are you sure about that? It seems very strange to me.
I could imagine Is tabhachtach é a bheith agat or something
or Is tabhachtach filíocht na hÉireann a bheith á léamh
but I am skeptical about Is tabhachtach é filíocht na hÉireann a léamh. working as you said with a pronoun.


Very interesting -- thank you!!!!!

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= It's important that you have it.


= It's important that Irish poetry is being read.


It's a normal verbal noun phrase:
subject + object + a + verbal noun
(perhaps a bit difficult to translate because English doesn't allow subjects in infinitive phrases. But Irish does.)

Yes those were clear. I wasn't trying to give alternative translations, just other examples.
Although the second one I was thinking "It's important that he read..." though I can see that it could also mean just being read.


So I see what you're saying and maybe it is because it is forbidden in English, but I was thinking that Irish would use a possessive here.
Is tabhachtach mo bheith ag léamh
or something instead of
Is tabhachtach mé a bheith ag léamh

like this one sounds perfectly normal
Is tabhachtach é a rá dó
something where the é is an object
but is it possible
Is tabhachtach é é a rá dó
[=it is important that he say it to him]
?????

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Wouldn’t that be possible in Keating’s Irish? I remember I read something that he would not use those infinitive-like phrases with a verb noun, as they were a later innovation coming from Scotland (so also is féidir liom do thuscint and not is féidir liom thú a thuiscint)? I am absolutely not sure that’s the case, as I never really studied how invinitive (or supine) phrases emerged in Irish, but I recall they are not that old.

Also, An Lon Dubh’s notes for Séadna’s caibideal 2 may be relevant here. See point 6. of Gramadach section.

There is an example with infinitive phrase after tar éis: tar éis an fhir a phosadh dom ‘after I married the man’ (tar éis forces the object, an fear to genitive, while ot also is an object).

But the sentence changes its structure and eliminates the infinitive phrase when a pronoun is an object (as I understand, because there can be no genitive pronoun after tar éis):
tar éis a phosta dom ‘after I married him’ and tar éis a posta dom ‘after I married her’ – now the whole verbal-noun-phrase goes info genitive, hence posta instead of posadh.

That kept me wondering if something like tar éis posta na mná dom or tar éis posta an fhir dom would be possible as an alternative way to say it – even if clumsy or archaic (and if archaic – if it was ever used).

You are mixing something up (progressive and verbal noun phrases)
First of all, I don’t think tabhachtach is used with the copula. I’d rather say "Tá sé tabhachtach go …"
If you'd use the copula I'd rather use a prepositional phrase is tabhachtach dó … = it's important for him …

So let’s use a different phrase (oh, here a subject is possible in English):
Ba mhaith leat mé (a) léamh = You'd like me to read.
Ba mhaith leat mé an leabhar a léamh = You'd like me to read the book.
or:
Ba mhaith leat mé a léamh an leabhair = You'd like me to read the book.

Let us again use another phrase
Ba mhaith liom é é a rá dó. = I'd like him to say it to him.
Still strange - but gramatically okay, I’d think.