I wasn't talking about "pregnant" and I personally don't care about it. "Unique" literally means "there is only one". Now where would you insert the word "most" in the sentence "there is only one"?
“When I use a word,” Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean—neither more nor less.” “The question is,” said Alice, “whether you can make words mean so many different things.” “The question is,” said Humpty Dumpty, “which is to be master—that’s all.”
When someone quotes a great author, they are often not standing on a single sentence, but on the larger meaning of some story signified by that sentence. Star Trek's Tamarians whole language was references to stories -- "Darmok and Jalad at Tanagra" is, for them, a highly compressed statement. So literature enormously expands our vocabulary, allowing us to use quotes as "pointers" to ideas much larger than anything we could state briefly.
"[Humpty said:] As I was saying, that seems to be done right — though I haven't time to look it over thoroughly just now — and that shows that there are three hundred and sixty-four days when you might get un-birthday presents —'
'Certainly,' said Alice.
'And only one for birthday presents, you know. There's glory for you!'
'I don't know what you mean by "glory",' Alice said.
Humpty Dumpty smiled contemptuously. 'Of course you don't — till I tell you. I meant "there's a nice knock-down argument for you!"'
'But "glory" doesn't mean "a nice knock-down argument",' Alice objected."
I think it is clear that Humpty's meaning was quite obvious, and Alice's complaint a bit dense. But while Humpty insists that he must tell Alice what he means, we can see that he needn't.
Of course, this word commanding business is as dangerous as you note, and Lewis Carroll is on the case:
"Alice was too much puzzled to say anything; so after a minute Humpty Dumpty began again. 'They've a temper, some of them — particularly verbs: they're the proudest — adjectives you can do anything with, but not verbs — however, I can manage the whole lot of them! Impenetrability! That's what I say!'
'Would you tell me please,' said Alice, 'what that means?'
'Now you talk like a reasonable child,' said Humpty Dumpty, looking very much pleased. 'I meant by "impenetrability" that we've had enough of that subject, and it would be just as well if you'd mention what you mean to do next, as I suppose you don't mean to stop here all the rest of your life.'
'That's a great deal to make one word mean,' Alice said in a thoughtful tone.
'When I make a word do a lot of work like that,' said Humpty Dumpty, 'I always pay it extra.'"
On the one hand, words can have many meanings, and any particular meaning must in part be taken from context. On the other hand, if we just try to _impose_ a meaning on a word, we defeat all communication, and make ourselves ridiculous to boot.
> When someone quotes a great author [it is for] the larger meaning of some story signified by that sentence.
That doesn't work when people are exchanging ideas on a forum and not everyone has read the same body of work. Because of the difficulty inherent in estimating who has read what, it is usually smart to avoid arguments "from the arts".
> allowing us to use quotes as "pointers" to ideas much larger than anything we could state briefly.
Larger than you could state briefly. Plus, aphorisms exist to fill in the gap you're talking about - all the benefits of brevity without the need for previous literary knowledge.
The excerpt you quoted reads like a boring story about a character that suffers from an affectation that makes him (her?) obsessed with trying to find reasons for using words loosely. I also didn't understand what he/she meant by "there's glory for you" even after the supposed explanation of what "glory" means in Dumpty's head.
This argument that "Shakespeare wrote this therefore it's right" doesn't work.
Read How to Speak and Write Correctly by Joseph Devlin for several instances of where Shakespeare made English mistakes and how to actually write correct English without appeal to authority.
That argument works, though, if we were speaking a language with a regulating body, such as French or Portuguese. Those regulating bodies define their languages in such a way that the "famous writers" never make mistakes. That's not the case with English. Let's keep English real. Shakespeare made several mistakes, read Devlin's grammar.
English isn't a compiled language. We can offer expressions that violate its "rules" and are still effective and powerful. It cannot be any other way. We know from Godel that no logical system can be consistent _and_ complete, so the use any human language must either admit violations of principle or accept limitations on what can be said in that language. It is the quality and success of the expression, not its compliance with grammatical rules, by which we judge expressions. The tests are "do you know what is meant" and "could it be said better", not "is it grammatical".
There are, therefore, no hard and fast authorities on English usage. English has principles and precedents, but not rules, and good writing is that which uses or violates those principles to communicate effectively. Shakespeare isn't an authority on usage, he's a compendium of examples of how usage can be harnessed for expression.
Now following those principles, and leveraging the readers' understanding and usage of them, allows far more expressive sentences. Gibbon writes enormous sentences that are clear as water and more efficient than any possible revision. Lincoln, by mastery of grammar, was able to express himself both powerfully and precisely. But the rules are in the service of expression, and good writers depart them when they don't permit the expression of what they want to say.
Complaints about the "mistakes" of great authors are generally mistakes about what the other meant to say, or insistence on some compliance that would damage brevity or power or nuance without adding any clarity. On ten minutes googling Devlin, I couldn't find a single "mistake" whose correction would clearly improve the sentence. Several of his examples miss the point, or weaken the sentence.
But if you want an authority, go to C.S. Lewis:
"About amn't I, aren't I and am I not, of course there are no right or wrong answers about language in the sense in which there are right and wrong answers in Arithmetic. . . . Don't take any notice of teachers and textbooks in such matters. Nor of logic. It is good to say "more than one passenger was hurt," although more than one equals at least two and therefore logically the verb ought to be plural were not singular was!"
Your Lewis quote contradicts your very first paragraph, as the quote argues languages aren't like logic and arithmetic, and in your first paragraph you assume languages are like logic and arithmetic enough to suffer from the same incompleteness problem (if I remember correctly only systems that include arithmetic can't be proven consistent?).
"More than one person is" is correct not because of any systematic reason, but because of euphony - it is more pleasing to the ear than "more than one person are". That, and whether the communication was effective, are the rulers of languages. That's how we got to where we are and how we go to where we are going. Not with central bodies regulating languages and not with language authorities we must emulate or check our usage against.
> Complaints about the "mistakes" of great authors are generally [...]
Yes, a lot of people have trouble accepting that even the greats make mistakes.
"My matter hath no voice, to your own most pregnant and vouchsafed ear." -- Viola, "Twelfth Night"