LotR -- Book 4 - Chapter 03 - The Black Gate Is Closed

[Lalwendë]

Originally Posted by Essex

But thinking about it, how would Gollum know you COULD destroy the ring by throwing it in to the cracks of doom?

To add to that, would Gollum even consider the fact that anyone would want to destroy his precious? He's probably very much like Sauron in that respect.

Another possibility of what he was up to might be that he knew the Hobbits were likely to be caught and so he could hope to get the ring under such circumstances. That he won't allow them through the Black Gate still allows for this possibility as he would be unlikely to want the Hobbits caught in such visible circumstances; a more chaotic capture in some hidden corner of Mordor would be more to his advantage.

Originally Posted by Essex

(come to think of it, how do gandalf and elrond know this - or was it an educated guess?)

I think that as ringbearers themselves, Gandalf and Elrond would know something of the history of how all the rings were made. Whether passed on by lore or through some sense conferred by the rings they bore, I'm not sure, though the latter would be the more attractive proposition given that the One now has power over all the rings.