For a metaphor to work it must appeal to another person’s unspoken sense of things--must validate "that which has already been privately apprehended but has gone unformulated for both of us."~ from The Life You Save May Be Your Own: An American Pilgrimage
This apprehended thing--"fugitive something"--is Being itself. Metaphor is a way to know Being. The structure of the world is metaphorical, and a metaphor bridges the gap between thing and Being--between Self and Other, between perception and reality, between the everyday and the transcendent--by naming it indirectly. "We can only conceive being, sidle up to it by laying something else alongside. We approach the thing not directly but by pairing, by apposing symbol and thing."
The argument is implicitly religious, but only in the last sentence of the essay does Percy invoke the Scholastic idea of the "analogy of being"--the idea that the natural world is the image of the supernatural one, and that we know "not as the angels know and not as dogs know but as men, who must know one thing through the mirror of another."
In the sunroom on Milan Street, he had reached a conclusion akin to those proposed by the others: Merton’s call for a restoration of the metaphors for religious experience, O’Connor’s notion of the artist’s task as the "accurate naming of the things of God," Day’s insistence that the Gospel is an instance of metaphor made real--that the poor stranger is not merely like Christ but is Christ, with all that this implies.
Last April, Ron Hogan posted an insightful exchange between Elie and Pankaj Mishra, author of An End to Suffering. I highly recommend giving it a look (scroll down to the bottom for the first entry and work your way up).