No. You may "guess" that the subsubject can be eliminated in cad é an rud san?, but it would be a bad guess. An rud san is the subject, and cannot stand next to the copula directly, and thus requires a subsubject. The fact that the copula is then deleted does not change the fact that the syntax here has to be (P)sS, where (P) represents the fact that cad is either the predicate or stands for the predicate, which will be given in the answer to the question.

Seósamh is ainm dom is the only way to phrase that, or Seósamh atá orm. But in Ua Laoghaire's Bible in Isaiah 42, we read Mise an Tiarna, sin é m’ainm.

Interesting. Thanks.

I haven't read your article (it's behind a paywall and seemingly not straightforward to pay) but your comment reminded me of Irish language placenames and the fact that they usually contain the definite article, but that a minority of the time the definite article is missing but seemingly implied.

For instance, placenames comprising of a lone noun, or noun followed by adjective, are usually preceded by the definite article e.g. An Sciobairín, An Daingean, An Ráth Mhór. However, maybe 10-15% of the time, the article is dropped e.g. Maigh Chromtha, Corcaigh, Doire, as if the noun in these cases is treated as being a proper noun in of itself and so not requiring the definite article. However, there doesn't seem to be any pattern as to when it is dropped versus retained i.e. it seems to me to be completely random.

I'm not sure how this compares with other countries/languages but maybe part of the reason that the definite article tends to be retained in Irish language placenames is that Irish language placenames are generally comprised of meaningful words and so the absence of the article might mislead the listener into thinking that the speaker is not referring to a placename at all and is instead simply treating the name as a common (and indefinite) noun.

On the other hand, if, for instance, I use Google Earth and zoom in to some random location in England, the placenames are generally meaningless words without the definite article (although there do seem to be a small few commonly re-occurring endings e.g. 'ham, 'by', 'ton'). Since English placenames seem not generally to be meaningful (i.e. not comprised of dictionary words), it's almost as if the names are treated as being intrinsically proper nouns, which might be why the inclusion of the definite article is rare. (Why Irish placenames have generally preserved their meanings but English placenames have apparently become corrupted is another topic. Maybe Irish placenames are generally not as old.)

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It seems that by far the most common grammatical structure in Irish placenames is a noun followed by a qualifying noun in the genitive case e.g. Sráid an Mhuilinn, Cathair na Mart, Cúil Aodha. But even here, when the qualifying noun is a common noun, the definite article is occasionally dropped (with there being no apparent pattern as to when this happens) e.g. Ceann Trá, Baile Eaglaise, when you might expect Ceann na Trá, Baile na hEaglaise.

The expression 'ceann trá' treated as a common noun phrase would mean 'a strand's end' (='the end of a strand') but as a proper noun it seems to be equivalent to saying 'Strand's End' (='End of Strand') in English, where the definite article is implied.

Also, the name Áth Cliath (Dublin) seems to be an example of this phenomonen in the plural, that implicitly means Áth na gCliath. This might be similar in English to saying 'Hurdle Ford' instead of 'The Hurdle Ford' (='The Ford of the Hurdles').

(This dropping of the article is something you also tend to see in English language newspaper headlines as a sort of shorthand e.g. 'Police shoot man with knife' would really mean 'The police shoot a man with a knife.')

Well, Caoilte, I can send you the article if you email me (foghlamthoir@gmail.com)

Djwebb, thanks for the offer. I'll send you an email.