Plato's Phaedo and STC's "Christabel" In Phaedo 80ff, Socrates outlines Plato's theory of Forms, particularly attempting to prove that the eternal Forms are of divine origin. Through analogy with the living body and the dead body, Socrates in dialogue with Cebes forces his interlocutor to admit that the body-soul dualism admits to a qualitative difference between the two, and then Socrates begins to describe the separation of body and soul, such as we would describe as a ghost:

"And, my friend, we must believe that the corporeal is burdensome and heavy and earthly and visible. And such a soul is weighed down by this and is dragged back into the visible world, through fear of the invisible and of the other world, and so, as they say, it flits about the monuments and the tombs, where shadowy shapes of souls have been seen, figures of those souls which were not set free in purity but retain something of the visible; and this is why they are seen."

"That is likely, Socrates."

"It is likely, Cebes. And it is likely that those are not the souls of the good, but those of the base, which are compelled to flit about such places as a punishment for their former evil mode of life. And they flit about until through the desire of the corporeal which clings to them they are again imprisoned in a body. And they are likely to be imprisoned in natures which correspond to the practices of their former life." (Phaedo 81c-e)

To a certain extent, the basic understanding of the soul here is wh-at is used by Coleridge to describe the unearthly Geraldine in his long poem-fragment "Christabel." In the poem, Coleridge relies upon the "corporeal" aspects of a supernatural presence in order to demonstrate its connection with "the base" and their "evil mode of life." Platonic notions about the inferiority of physical existence combine with much-modified Christian notions of good and evil to result in Coleridge's image of a lesbian vampire.

The moment...

The reader is asked to imagine Geraldine's naked body, which is "a sight to dream of, not to tell" -- suggesting the Platonic disconnection between the eternal and ineffable essence of things, and their (flawed) physical manifestation on earth. Yet "dream" sounds almost positive -- we are not expecting that something described as a "dream" could be menacing enough to cause the narrator to break off and invoke the heavens to protect his heroine.
Michael Gamer describes the complicated history of the composition of "Christabel"; Coleridge would write the first part of the poem in 1797, expecting inclusion in the joint volume of Lyrical Ballads that Coleridge would publish with Wordsworth the next year. But Coleridge would write a second part of the poem, in anticipation of the revised edition of Lyrical…