LotR -- Book 6 - Chapter 2 - The Land of Shadow

[Kuruharan]

Why would the Ring know this? I don't think so at all. The Ring knew that he was born by Frodo, and that there were Nazgûl at hand.

If the Ring could sense the Nazgul, what possible reason could you propose that it could not sense Gandalf? Gandalf actually touched the Ring you must recall, when he threw it into the fire at Bag End. The Ring had to have known that a being of great power set against its master was there (and doing strange things to it to boot).

And before everyone gets all carried away, I think another little bit of wisdom from that incident might help here.

And even so he would never have just forsaken it, or cast it aside. It was not Gollum, Frodo, but the Ring itself that decided things. The Ring left him.