Summa contra Gentiles1.66 Chapter LXVI. That God knows the things that are not

In the next place we must show that God lacks not the knowledge of things that are not.

For as stated above the divine knowledge stands in the same relation to the things known, as things knowable to our knowledge. Now the comparison of the thing knowable to our knowledge is that the knowable thing may exist without our having knowledge of it, whereof the Philosopher in the Predicaments gives the example of squaring the circle; but not conversely. Wherefore the relation of the divine knowledge to things must be such that it can also relate to non-existent things.

Again. The knowledge of God's intellect stands in the same relation to other things as the knowledge of a craftsman to the works of his craft: since He is cause of things by His knowledge. Now the craftsman by the knowledge of his art knows even those things which are not yet produced by his art: since the forms of his art pass from his knowledge into external matter so as to produce the works of his art: and consequently nothing prevents forms which have not yet materialized outwardly from being in the craftsman's knowledge. Therefore nothing prevents God from having knowledge of things that are not.

Further. God knows things other than Himself by His essence, in as much as He is the likeness of the things that proceed from Him, as shown above. But, since God's essence is infinitely perfect, as proved above, while all things else have limited being and perfection, it is impossible for all other things together to equal the perfection of the divine essence. Wherefore it is capable of representing many things besides those that exist. Hence if God knows the whole power and perfection of His essence, His knowledge extends not only to those things that are, but also to those that are not.

Moreover. Our intellect, in respect of the operation by which it knows what a thing is, can have knowledge of those things also that are not actually: since it is able to comprehend the essence of a lion or horse, even if all such animals were slain. Now the divine intellect knows, as one who knows what a thing is, not only definitions but also enunciations, as shown above. Therefore it can have knowledge of those things also that are not.

Again. An effect can be foreknown in its cause even before it exist: even so an astronomer foreknows a future eclipse by observing the order of the heavenly movements. Now God's knowledge is of all things through their cause: for by knowing Himself, Who is the cause of all, He knows other things as His effects, as we proved above. Nothing, therefore, prevents Him from knowing those things also that are not yet.

Moreover. There is no succession in God's act of understanding, any more than there is in His existence. Hence it is all at once everlasting, which belongs to the essence of eternity, whereas the duration of time is drawn out by the succession of before and after. Wherefore the proportion of eternity to the whole duration of time is as the proportion of the indivisible to the continuous, not indeed of the indivisible that is the term of the continuous, and is not present to each part of the continuous—for such is likened to an instant of time—but of the indivisible that is outside the continuous, and yet synchronizes with each part of the continuous, or with each point of a signate continuous: because, since time does not exceed movement, eternity, being utterly outside movement, is altogether outside time. Again, since the being of the eternal never fails, eternity synchronizes with every time or instant of time. Somewhat of an example of this may be seen in the circle: for a given point in the circumference, although indivisible, does not coincide in its position with any other point, since the order of position results in the continuity of the circumference; while the centre which is outside the circumference is directly opposite any given point in the circumference. Accordingly whatever exists in any part of time, is coexistent with the eternal as though present thereto, although in relation to another part of time it is present or future. Now a thing cannot be present to, and coexistent with, the eternal, except with the whole eternal, since this has no successive duration. Therefore whatever happens throughout the whole course of time is seen as present by the divine intellect in its eternity. And yet that which is done in some part of time was not always in existence. It remains therefore that God has knowledge of those things which are not as yet in relation to the course of time.

By these arguments it is made clear that God has knowledge of not-beings. Nevertheless not-beings have not all the same relation to His knowledge. For those things which neither are, nor shall be, nor have been, are known by God as possible to His power. Wherefore He knows them, not as existing in themselves in any way, but as merely existing in the divine power. Such things are said by some to be known to God according to His knowledge of simple intelligence.

On the other hand things which to us are present, past, or future, are known to God as being not only in His power, but also in their respective causes, and in themselves. Of such things God is said to have knowledge of vision, because God sees the existence of things which, in relation to us, are not as yet, not only in their causes but also in themselves, in as much as His eternity is by its indivisibility present to all time.

Yet God knows every manner of a thing's being by His essence. For His essence is capable of being represented by many things that neither are, nor shall be, nor have been. Moreover it is the likeness of every cause's power, in respect of which effects pre-exist in their causes. And the being that every single thing has in itself is drawn as a copy from Him.

Wherefore God knows not-beings in so far as they have being after a fashion, either in the divine power, or in their causes, or in themselves. And this is not contrary to the essential conditions of knowledge.

The authority of Holy Writ also bears witness to the foregoing. For it is written (Ecclus. xxiii. 29): All things were known to the Lord God, before they were created; so also after they were perfected He knoweth all things; and (Jer. i. 5): Before I formed thee in the womb, I knew thee.

It is clear from what has been said, that we are not compelled to say, as some have said, that God knows all singulars universally, because He knows them in their universal causes only, even as one who knows a particular eclipse, not as this particular one, but as resulting from opposition: since it has been proved that the divine knowledge extends to singulars as existing in themselves.