The reply to him is:

This question arises only from the mistaken impression that half the celestial sphere lies beneath the earth and beneath the human beings and animals on its surface. This is a grave error. If the celestial sphere were beneath the earth on one side, it would be beneath it on every side. This would necessarily mean that the celestial sphere was beneath the earth without qualification—a reversal of reality, since the celestial sphere is above the earth without qualification.

Astronomers say:

If a hole were bored through the earth in the direction of our feet, and a heavy object, such as a stone, were dropped into it, the object would come to rest at the centre. Indeed, if another stone were dropped from the opposite side, the two would meet at the centre. If we supposed that two people met at the centre instead of the two stones, their feet would meet, and neither would be beneath the other. Rather, both would be above the centre, and both beneath the celestial sphere.

The same applies to east and west. If we supposed that one man was in the east, in the sky or on the earth, and another in the west, in the sky or on the earth, neither would be beneath the other. This would be so regardless of whether his head, feet, stomach, back or side faced the sky or the earth. If either of them sought what is above the celestial sphere, he would seek it only in the upward direction, not in the direction of his feet, or to his right or left, for two reasons.

The first is that what he seeks is nearer to him in the upward direction than in any other direction. If we supposed that a man or an angel were ascending to the sky, or to what is above it, the shortest ascent would be in the direction of his head, if that were possible for him.

No rational person would say that he should bore through the earth and then ascend from the other side, nor that he should go right or left, forwards or backwards, to