Revelations and Realizations

[Guinevere]

it didn't stop him nicking and adapting for Aragorn the "All that glisters is not gold" line from Merchant of Venice.

Now that is just a common, widespread proverb, so you can't say Tolkien quoted Shakespeare when he used it! (and he turned it around: "all that is gold does not glitter"!)

And apropos the witches in Macbeth: in "On Fairy-stories" Tolkien wrote that he thought them tolerable when just reading the play, but on stage he didn't approve of them at all! (And he did write about Shakespeare "Which I disliked cordially" in letter 163)

I am quite sure he did not use that phrase! I'm fairly certain I would have noticed and not forgotten about it. (If I think of all the "proverbs" and wise sayings I collected... Have a look at the quotable quotes, ninlaith, you can see that there are people here who do remember lots of sentences literally!)