But in the 15th Century English grammar rules were nonexistent. During Shakespeare’s time grammar rules were at its inchoate stage and Shakespeare rarely adhered to grammatical constructions. 

That’s nonsensical. Of course Shakespeare’s writing is grammatical. And they did have written rules of grammar. Shakespeare attended a grammar school in his youth.

I was responding to your statement that Shakespeare used the objective “who”. In modern English the standard usage would be in the subjective case. Why would the fact that Shakespeare used it in the objective case have any relevancy to modern English usage?  I agree that Shakespeare’s writing is grammatical, but I never specifically stated that Shakespeare’s writing was ungrammatical. I said that in the 15th century English grammar rules were nonexistent, meaning that grammar rules at that time were not stringently adhered to. Furthermore those rules were modeled on Latin grammars. Shakespeare had broken some of the rules at some time in some of his works. It was only during the 19th century that English grammar rules were codified.  Regarding Shakespeare’s education, there is in fact no record of Shakespeare’s name on the register of the King Edward VI Grammar School in Stratford; reasonable assumptions can be made; nevertheless it’s not a certainty.

Shakespeare also did not use the structured rule, subject, verb, object. “Hamlet, thou hast thy father much offended.” In present day English we would expect, “Thou has much offended thy father Hamlet.”

Of course he did. The Hamlet in both of these phrasings is a vocative, indicating who the subject (thou) refers to. The core of the clause, thou has offended your father, is a very standard SVO clause. (And in present-day English, we would expect Hamlet, you have offended your father, not Hamlet thou hast thy father offended.)

That’s precisely my argument; that in present-day English no one would say e.g., Hamlet, you have your father offended. It would seem an unorthodox construction, and just because Shakespeare used it five hundred years ago doesn’t make it applicable for modern English usage.

And if the argument is that they didn’t have grammar manuals back then, that’s wrong too. Grammar manuals for English date to the tenth century.

Never argued that; my only knowledge of the first English grammar manual was William Bullokar’s Pamphlet for Grammar published in 1586.
I wasn’t aware of any English grammar manuals going back to the tenth century. What were they?

Regarding Shakespeare’s education, there is in fact no record of Shakespeare’s name on the register of the King Edward VI Grammar School in Stratford

That’s a misleading statement. It’s not Shakespeare’s name that we don’t have, it’s the entire register for the period that doesn’t survive. (This isn’t a mere quibble; many anti-Stratfordians claim hotly that Shakespeare was illiterate because ‘There’s no evidence he ever went to grammar school!!!’, carefully omitting the fact that there is no direct evidence that any specific boy in 16th-century Stratford attended its grammar school.)

Shakespeare also did not use the structured rule, subject, verb, object. “Hamlet, thou hast thy father much offended.” In present day English we would expect, “Thou has much offended thy father Hamlet.”

Well, I for one wouldn’t. I would expect anyone using the archaic second-person thou at all to use the appropriate archaic second-person verb form, in this case hast. ‘Thou has’ looks and sounds terrible - and wholly ungrammatical - to me, and I bet it would have to Shakespeare too.

That’s precisely my argument; that in present-day English no one would say e.g., Hamlet, you have your father offended. It would seem an unorthodox construction, and just because Shakespeare used it five hundred years ago doesn’t make it applicable for modern English usage.

I suspect that nobody in real life would have said ‘thou hast thy father much offended’ in Shakespeare’s day, either. But Shakespeare was writing in iambic pentameters, and ‘Hamlet, thou hast much offended thy father’ isn’t a pentameter, and can only be made one by inverting the normal word order. And there is nothing whatsoever ‘unorthodox’ about that; a certain amount of jiggery-pokery with word order to make lines scan and rhyme has been considered legit in poetry from before Shakespeare’s time right up to the present day, insofar as anyone these days writes scanned verse.

I said that in the 15th century English grammar rules were nonexistent, meaning that grammar rules at that time were not stringently adhered to.

That’s the nonsensical part. Grammar rules are based on how people use the language. If they don’t speak and write that way, it’s not a rule. There is no objectively correct grammar.

(By “no objectively correct” I do not mean that something cannot be ungrammatical. Thou has is ungrammatical, for instance, because it doesn’t follow the usual pattern in either early modern or present-day English. The nominative/objective distinction between who and whom has never been observed, except in present-day edited writing, so to use an objective who is not ungrammatical and never has been.)

The earliest English grammar I know of is Ælfric’s, written in the closing years of the tenth century. I’ll bet there are some Middle English grammars out there too, but I’m not an expert on the ME corpus.

Regarding Shakespeare’s education, there is in fact no record of Shakespeare’s name on the register of the King Edward VI Grammar School in Stratford

That’s a misleading statement. It’s not Shakespeare’s name that we don’t have, it’s the entire register for the period that doesn’t survive. (This isn’t a mere quibble; many anti-Stratfordians claim hotly that Shakespeare was illiterate because ‘There’s no evidence he ever went to grammar school!!!’, carefully omitting the fact that there is no direct evidence that any specific boy in 16th-century Stratford attended its grammar school.)

Perhaps it is a misleading statement; nevertheless, there is no record, and from the little we know Shakespeare’s scholastic education was quite limited.  Regardless, the argument is moot because in reality, apart from bits of little information there is nothing clear-cut or any revealing documentation on Shakespeare. The bare facts are a little imprecise. 

I suspect that nobody in real life would have said ‘thou hast thy father much offended’ in Shakespeare’s day, either. But Shakespeare was writing in iambic pentameters, and ‘Hamlet, thou hast much offended thy father’ isn’t a pentameter, and can only be made one by inverting the normal word order.

Shakespeare did not always write in Iambic pentameter. Actually, much of Shakespeare’s plays were not written in verse there was quite a bit of prose in Shakespeare’s works.  Furthermore, “ Hamlet, thou hast thy father much offended”, which is in act 3 scene 4, is prose dialogue,(inverted or not) between Hamlet and his mother, Gertrude. It is not written in Iambic pentameter.

And there is nothing whatsoever ‘unorthodox’ about that; a certain amount of jiggery-pokery with word order to make lines scan and rhyme has been considered legit in poetry from before Shakespeare’s time right up to the present day, insofar as anyone these days writes scanned verse.

Correct, if you’re referring exclusively to poetry, but words do not need to rhyme in prose, but they do require a certain grammatical order. And again, Shakespeare did not write entirely in verse. Some of Shakespeare’s plays are almost all in prose.

Regardless, my point is that just because Shakespeare used, what might be considered an unorthodox expression five hundred years ago, doesn’t make it applicable for modern English usage.

Grammar rules are based on how people use the language.

A debatable topic, which I defer to others to argue.

Regardless, the argument is moot because in reality, apart from bits of little information there is nothing clear-cut or any revealing documentation on Shakespeare.

That’s another myth. We have an incredible amount of source documentation on Shakespeare, far more than most other people of the age.

Regardless, my point is that just because Shakespeare used, what might be considered an unorthodox expression five hundred years ago, doesn’t make it applicable for modern English usage.

It’s the premise that’s incorrect. The objective use of who was not unorthodox five hundred years ago. It was quite ordinary, just as it is today.

You’re right in that how Elizabethans used language is not relevant to how we use the language today, but my bringing Shakespeare up was not to say that. It was to make the point that there was never any rule about the objective who and that the contention that whom is rapidly disappearing isn’t correct.

A debatable topic, which I defer to others to argue.

No, it’s not debatable. Language is what we make of it. There is no objective standard of correctness to language.