The Ringwraiths -- What were they?

[obloquy]

Obloquy, Mithadan was talking about Sauron practicing necromancy on dead Elves, not dead Men. Nothing can bring back a Man who has died, except Eru Himself.

This is exactly my point. Sauron's necromancy can't explain the Nazgul.

You go on to explain your opinion of the Nazgul, which I almost wholly agree with, and was precisely the idea I intended to convey in my post. The only point I don't necessarily agree on is that the Nazgul are occasionally separated from their hroar. I believe LotR only mentions the Nine being unhorsed, not actually "destroyed" in any sense.

As I said in a previous post -- and you also included in yours -- the Nazgul can't be actual ghosts (read dead), because Sauron can't bind the fea of a Man. A Man's fea doesn't return to Aman to serve its time in Mandos, and it doesn't get rehoused. Can Sauron keep the fea of a mortal Man from its fate? was my question to Mithadan because his explanation of the nature of the Nazgul was based on Sauron's necromancy (at least it seemed so to me). Which, I reiterate, I don't think is possible.

Gandalf alludes to the Nazgul being dead, however.

`I know,' said Frodo. `They were terrible to behold! But why could we all see their horses?'
`Because they are real horses; just as the black robes are real robes that they wear to give shape to their nothingness when they have dealings with the living.'

And this is why I asked the question. I had always just assumed they were dead, but I now don't think they could be. Your opinion, Elenhin, that I agree with, seems the most plausible. It explains why they were affected by physical objects, and why they could affect the physical.