Eldil: Spirit, Ghost, Angel?
As to my intense wish never to come into contact with the eldila myself, I am not sure whether I can make you understand it. It was something more than a prudent desire to avoid creatures alien in kind, very powerful, and very intelligent. The truth was that all I heard about them served to connect two things which one’s mind tends to keep separate, and that connecting gave one a sort of shock. We tend to think about non-human intelligences in two distinct categories which we label “scientific” and “supernatural” respectively. We think, in one mood, of Mr. Wells’ Martians…or his Selenites. In quite a different mood we let our minds loose on the possibility of angels, ghosts, fairies, and the like. But the very moment we are compelled to recognise a creature in either class as real the distinction begins to get blurred: and when it is a creature like an eldil that distinction vanishes altogether. These things were not animals– to that extent one had to classify them with the second group; but they had some kind of material vehicle whose presence could (in principle) be scientifically verified. To that extent they belonged to the first group. The distinction between natural and supernatural, in fact, broke down; and when it had done so, one realised how great a comfort it had been– how it had eased the burden of intolerable strangeness which this universe imposes on us by dividing it into halves and encouraging the mind never to think of both in the same context. What price we may have paid for this comfort in the way of false security and accepted confusion of thought is another matter.
-C.S. Lewis, Perelandra, Chapter 2