The Discarded Image was the last book that C.S. Lewis wrote. It is a pedagogical book, written primarily for the purposes of teaching his students of Renaissance and Medieval literature about the picture or ‘model’ of the universe that was then universally accepted. This model is entirely foreign to us now, and is known only to those who have purposefully sought out a knowledge of antique and medieval cultural history. Where this knowledge persists it does so usually as a kind of apologetic against Christianity which asserts (in error) that before the rise of modern science everybody thought that the world was flat or that the stars were very close to the earth or that the earth was the centre and hence most important of the universe; these beliefs are usually traced to their source in the Christian Bible, which of course says nothing of the sort and is certainly not the originator of the Medieval model. I had not heard of Lewis’ book before I came across a footnote in David Bentley Hart’s The Experience of God and so I will use his useful (and surprisingly succinct) description of the discarded image.
(The) antique, medieval, and early modern universe (was) described in an “incomplete” form by Aristotle (384-322 BC) and given its most enduring finishing touches by Ptolemy (AD c. 90-c. 168). The earth stood immovably at the center of the system of interlocking heavens: immutable transparent spheres, each save one of them immediately encompassed by another larger than itself, in a regular succession upward and outward; each of the first seven sphere contained a “planet” (in order, the moon, Mercury, Venus, the sun, Mars, Jupiter, and Saturn), the next beyond those was the stellatum, or region of the fixed stars, and the next beyond that the mysterious primum mobile , or “first moveable” heaven. Beyond that, however, lay the “realm” of the Unmoved Mover, understood either as a changeless spiritual intellect not directly involved in lower things, a pure “thought thinking thought,” or as God the active creator of the universe.
David Bentley Hart, The Experience of God: Being, Consciousness, Bliss
As many others still do, Lewis found this model to be an exceptionally beautiful, creative and life-giving picture of the universe. The spheres described above rotate as a result of the movement of the primum mobile (rotation being their most approximate expression of God’s perfection and immutability), which is in turn moved by God, the Unmoved Mover himself. They do this absolutely consistently and so constitute a realm of greater perfection and immutability than the realm in which we live, the Earth, and the sky above us, which is constantly afflicted by the changeability and corruption that we call the weather (especially those of who live here in England, although I’m writing on a sunny and pleasant July morning in North-East London). But the question of how God, who is unmoved and cannot be said to move in order to move anything else, can cause the primum mobile to move is an important one. And the answer that the antique world gave to us is perhaps the most beautiful and poetic aspect of this discarded image:
There must in the last resort be something which, motionless itself, initiates the motion of all other things. Such a Prime Mover, (Aristotle) finds in the wholly transcendent and immaterial God who ‘occupies no place and is not affected by time’ (Aristotle, De Caelo). But we must not imagine him moving things by any positive action, for that would be to attribute some kind of motion to Himself and we should then not have reached an utterly unmoving Mover. How then does He move things? Aristotle answers, κινει ως ερωμενον, ‘He moves as beloved’ (Aristotle, Metaphysics). He moves other things, that is, as an object of desire moves those who desire it. The Primum Mobile is moved by its love for God, and being moved, communicates motion to the rest of the universe…This all implies that each sphere, or something resident in each sphere, is a conscious and intellectual being, moved by “intellectual love” of God.
CS Lewis, The Discarded Image
This explanation sheds light on one of the most beautiful verses in all literature, and this is the final stanza of Dante’s Comedia, Paradisio 33:
But my desire and will were moved already—
like a wheel revolving uniformly—by
the Love that moves the sun and the other stars.