And the invisible divine reason, perceptible only by intellect, he calls the image of God. And the image of this image is that light, perceptible only by the intellect, which is the image of the divine reason, which has explained its generation. And it is a star above the heavens, the source of those stars which are perceptible by the external senses, and if any one were to call it universal light he would not be very wrong; since it is from that the sun and the moon, and all the other planets and fixed stars derive their due light, in proportion as each has power given to it; that unmingled and pure light being obscured when it begins to change, according to the change from that which is perceptible only by the intellect, to that which is perceptible by the external senses; for none of those things which are perceptible to the external senses is pure.
 Moses is right also when he says, that darkness was over the face of the abyss. For the air is in a manner spread above the empty space, since having mounted up it entirely fills all that open, and desolate, and empty place, which reaches down to us from the regions below the moon. And after the shining forth of that light, perceptible only to the intellect, which existed before the sun, then its adversary darkness yielded, as God put a wall between them and separated them, well knowing their opposite characters, and the enmity existing between their natures. In order, therefore, that they might not war against one another from being continually brought in contact, so that war would prevail instead of peace, God, turning want of order into order, did not only separate light and darkness, but did also place boundaries in the middle of the space between the two, by which he separated the extremities of each. For if they had approximated they must have produced confusion, preparing for the contest, for the supremacy, with great and unextinguishable rivalry, if boundaries established between them had not separated them and prevented them from clashing together, and these boundaries are evening and morning; the one of which heralds in the good tidings that the sun is about to rise, gently dissipating the darkness: and evening comes on as the sun sets, receiving gently the collective approach of darkness. And these, I mean morning and evening, must be placed in the class of incorporeal things, perceptible only by the intellect; for there is absolutely nothing in them which is perceptible by the external senses, but they are entirely ideas, and measures, and forms, and seals, incorporeal as far as regards the generation of other bodies. But when light came, and darkness retreated and yielded to it, and boundaries were set in the space between the two, namely, evening and morning, then of necessity the measure of time was immediately perfected, which also the Creator called day. and He called it not the first day, but one day; and it is spoken of thus, on account of the single nature of the world perceptible only by the intellect, which has a single nature.