I was in the seminar the other day and the speaker quoted a line. I wanted to ask a question - so can you tell me which one of the above would have been appropriate ? Is there any difference ?
The following variations are all correct. They all mean the same thing:
Is it a Shakespeare quote? (Using his name as an attributive noun.)
Is it a Shakespearean quote? (This is the adjective form.)
Does that quote come from Shakespeare?
If you had a few quotes to choose from (such as one from the King James Bible, one from Milton, and one from Shakespeare), it would be appropriate to ask "Is it Shakespeare's quote?" In this usage, the possessive is used to indicate the particular quote. This makes the indefinite article "a" redundant. It is incorrect to ask "Is it a Shakespeare's quote?"
By the way, Shakspere could spell his own name... several different ways.
Though I cannot say that it is grammatically incorrect, I don't think I've heard of English Speakers using possessive before the word "quote." You could say it's a "quote from Shakespeare", or it's a "Shakespeare quote". I think the difference is that when people talk of Shakespeare in this sort of context, they mean "Shakespeare's collective works", and not the man himself.
You could even possibly say "quote by Shakespeare", although then in this phrase, Shakespeare must be the man who created the quote, and not his collective works.