Theirs was not exactly a textbook friendship: What grammar construction is used here?

Question

Here is a sentence from a short story by James Gripando:

Theirs was not exactly a textbook friendship, the Ivy League son of a governor meets the black high-school dropout from Liberty City.

If the first part of it read "Their friendship was not a textbook one", there'd be no question. But as it is, is its subject still their friendship? Looks like it is split, and this made me search for the rule allowing it. The best I could find was this definition:

A split subject is a construction in which the subject of a sentence appears to consist of two parts that do not appear next to each other.

(The source)

Yet, on reading the article, I could see that the grammar construction described there has little if anything to do with that used in " Theirs was not exactly a textbook friendship".

What is the correct term of what I thought to be a split subject? How and when this grammar construction may be used?

Answer 1

Mine is a different answer from Andrew's.

This is not a literary construction at all, but something we could hear almost anywhere. The possessive pronoun simply anticipates its referent noun.

Theirs is a much bigger house than ours.

My brother has a brand new Mercedes. Ours is a much less expensive car.

Mine is the sundae with the whipped cream and the cherry on top.

Yours is the dog with the long hair, right?

By moving the pronoun to the head of the sentence, it receives special emphasis, usually to draw attention to a difference between the thing as possessed by or as it belongs to {him, her, them, me, you, us} and the thing as possessed by or belonging to others.

Answer 2

This is a somewhat literary sentence construction, almost like the start of a story, but while it is slightly dramatic it's not uncommon.

"Theirs was not exactly a textbook friendship," is equivalent to, "Their friendship was not exactly textbook," and so friendship remains the subject of the sentence. The second part of the sentence describes why the friendship was unusual.

I wouldn't say it's an example of a split subject as you reference. Those seem to require a repetition or duplication of the subject, used in vernacular, and not "correct" formal English. Your example is, however, grammatically correct.

Another example of the same type:

Theirs was a terrifying beast, not so much a tomcat as a Machiavellian demon whose astounding technique for soliciting food involved equal parts obsequiousness and extortion.

Although the language is picturesque, the subject is still "their cat". Another:

His was not a great work of art, but merely the best a humble artisan could produce with the tools he was given.

The subject is "his art", not great art but still not bad.

One more somewhat related example (mostly for fun). You can't get more literary than Dickens' "A Tale of Two Cities":

It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, we had everything before us, we had nothing before us, we were all going direct to Heaven, we were all going direct the other way – in short, the period was so far like the present period, that some of its noisiest authorities insisted on its being received, for good or for evil, in the superlative degree of comparison only.

Here "it" means "the current time", although here (in contrast to your example) Dickens uses repetition of the "it was ..." to suggest what the times were, instead of writing a more clear description.