Slaying of the Witch king

[tom bombariffic]

How can Glorfindel's prophecy not be relevant? He had foreseen that the Witch King would die under particular circumstances, and so the Witch King was always going to die in those circumstances.

Yes, he had forseen that it would happen. Hence his prophecy. But him making the prophecy was not THE REASON for a man not being able to kill him. The fact that he would end up dying at the hands of someone other than a man is not BECAUSE Glorfindel made the prophecy. On the contrary, Glorfindel made the prophecy because he had forseen what would happen - but the fact that Glorfindel noticed makes not difference - Had he made the prophecy or not, the outcome would have been the same.