[Vicious Love]

Ding! Gandalf sez: "Some here will remember that many years ago I myself dared to pass the doors of the Necromancer in Dol Guldur, and secretly explored his ways, and found thus that our fears were true: he was none other than Sauron, our Enemy of old, at length taking shape and power again."

Further, Tolkien sez: "It was thus that Sauron appeared in this shape. It is mythologically supposed that when this shape was 'real', that is a physical actuality in the physical world and not a vision transferred from mind to mind, it took some time to build up. It was then destructible like other physical organisms. But that of course did not destroy the spirit, nor dismiss it from the world to which it was bound until the end. After the battle with Gilgalad and Elendil, Sauron took a long while to re-build, longer than he had done after the Downfall of Númenor (I suppose because each building-up used up some of the inherent energy of the spirit, that might be called the 'will' or the effective link between the indestructible mind and being and the realization of its imagination). The impossibility of re-building after the destruction of the Ring, is sufficiently clear 'mythologically' in the present book."

Thanks to some pedantic purist at minastirith.com for digging this latter quote up in my stead.