Summa Theologica, Part I (Prima Pars) From the Complete...

Having considered what belongs to the divine substance, we have now to treat of God's operation. And since one kind of operation is immanent, and another kind of operation proceeds to the exterior effect, we treat first of knowledge and of will (for understanding abides in the intelligent agent, and will is in the one who wills); and afterwards of the power of God, the principle of the divine operation as proceeding to the exterior effect. Now because to understand is a kind of life, after treating of the divine knowledge, we consider the divine life. And as knowledge concerns truth, we consider truth and falsehood. Further, as everything known is in the knower, and the types of things as existing in the knowledge of God are called ideas, to the consideration of knowledge will be added the treatment of ideas.

I answer that, In God there exists the most perfect knowledge. To prove this, we must note that intelligent beings are distinguished from non-intelligent beings in that the latter possess only their own form; whereas the intelligent being is naturally adapted to have also the form of some other thing; for the idea of the thing known is in the knower. Hence it is manifest that the nature of a non-intelligent being is more contracted and limited; whereas the nature of intelligent beings has a greater amplitude and extension; therefore the Philosopher says (De Anima iii) that "the soul is in a sense all things." Now the contraction of the form comes from the matter. Hence, as we have said above (Q. 7, A. 1) forms according as they are the more immaterial, approach more nearly to a kind of infinity. Therefore it is clear that the immateriality of a thing is the reason why it is cognitive; and according to the mode of immateriality is the mode of knowledge. Hence it is said in De Anima ii that plants do not know, because they are wholly material. But sense is cognitive because it can receive images free from matter, and the intellect is still further cognitive, because it is more separated from matter and unmixed, as said in De Anima iii. Since therefore God is in the highest degree of immateriality as stated above (Q. 7, A. 1), it follows that He occupies the highest place in knowledge.

Reply Obj. 1: Because perfections flowing from God to creatures exist in a higher state in God Himself (Q. 4, A. 2), whenever a name taken from any created perfection is attributed to God, it must be separated in its signification from anything that belongs to that imperfect mode proper to creatures. Hence knowledge is not a quality of God, nor a habit; but substance and pure act.

Reply Obj. 2: Whatever is divided and multiplied in creatures exists in God simply and unitedly (Q. 13, A. 4). Now man has different kinds of knowledge, according to the different objects of His knowledge. He has intelligence as regards the knowledge of principles; he has science as regards knowledge of conclusions; he has wisdom, according as he knows the highest cause; he has counsel or prudence, according as he knows what is to be done. But God knows all these by one simple act of knowledge, as will be shown (A. 7). Hence the simple knowledge of God can be named by all these names; in such a way, however, that there must be removed from each of them, so far as they enter into divine predication, everything that savors of imperfection; and everything that expresses perfection is to be retained in them. Hence it is said, "With Him is wisdom and strength, He hath counsel and understanding" (Job 12:13).

Reply Obj. 3: Knowledge is according to the mode of the one who knows; for the thing known is in the knower according to the mode of the knower. Now since the mode of the divine essence is higher than that of creatures, divine knowledge does not exist in God after the mode of created knowledge, so as to be universal or particular, or habitual, or potential, or existing according to any such mode. _______________________

Objection 1: It seems that God does not understand Himself. For it is said by the Philosopher (De Causis), "Every knower who knows his own essence, returns completely to his own essence." But God does not go out from His own essence, nor is He moved at all; thus He cannot return to His own essence. Therefore He does not know His own essence.

Obj. 2: Further, to understand is a kind of passion and movement, as the Philosopher says (De Anima iii); and knowledge also is a kind of assimilation to the object known; and the thing known is the perfection of the knower. But nothing is moved, or suffers, or is made perfect by itself, "nor," as Hilary says (De Trin. iii), "is a thing its own likeness." Therefore God does not understand Himself.

Obj. 3: Further, we are like to God chiefly in our intellect, because we are the image of God in our mind, as Augustine says (Gen. ad lit. vi). But our intellect understands itself, only as it understands other things, as is said in De Anima iii. Therefore God understands Himself only so far perchance as He understands other things.

I answer that, God understands Himself through Himself. In proof whereof it must be known that although in operations which pass to an external effect, the object of the operation, which is taken as the term, exists outside the operator; nevertheless in operations that remain in the operator, the object signified as the term of operation, resides in the operator; and accordingly as it is in the operator, the operation is actual. Hence the Philosopher says (De Anima iii) that "the sensible in act is sense in act, and the intelligible in act is intellect in act." For the reason why we actually feel or know a thing is because our intellect or sense is actually informed by the sensible or intelligible species. And because of this only, it follows that sense or intellect is distinct from the sensible or intelligible object, since both are in potentiality.

Since therefore God has nothing in Him of potentiality, but is pure act, His intellect and its object are altogether the same; so that He neither is without the intelligible species, as is the case with our intellect when it understands potentially; nor does the intelligible species differ from the substance of the divine intellect, as it differs in our intellect when it understands actually; but the intelligible species itself is the divine intellect itself, and thus God understands Himself through Himself.

Reply Obj. 1: Return to its own essence means only that a thing subsists in itself. Inasmuch as the form perfects the matter by giving it existence, it is in a certain way diffused in it; and it returns to itself inasmuch as it has existence in itself. Therefore those cognitive faculties which are not subsisting, but are the acts of organs, do not know themselves, as in the case of each of the senses; whereas those cognitive faculties which are subsisting, know themselves; hence it is said in De Causis that, "whoever knows his essence returns to it." Now it supremely belongs to God to be self-subsisting. Hence according to this mode of speaking, He supremely returns to His own essence, and knows Himself.

Reply Obj. 2: Movement and passion are taken equivocally, according as to understand is described as a kind of movement or passion, as stated in De Anima iii. For to understand is not a movement that is an act of something imperfect passing from one to another, but it is an act, existing in the agent itself, of something perfect. Likewise that the intellect is perfected by the intelligible object, i.e. is assimilated to it, this belongs to an intellect which is sometimes in potentiality; because the fact of its being in a state of potentiality makes it differ from the intelligible object and assimilates it thereto through the intelligible species, which is the likeness of the thing understood, and makes it to be perfected thereby, as potentiality is perfected by act. On the other hand, the divine intellect, which is no way in potentiality, is not perfected by the intelligible object, nor is it assimilated thereto, but is its own perfection, and its own intelligible object.

Reply Obj. 3: Existence in nature does not belong to primary matter, which is a potentiality, unless it is reduced to act by a form. Now our passive intellect has the same relation to intelligible objects as primary matter has to natural things; for it is in potentiality as regards intelligible objects, just as primary matter is to natural things. Hence our passive intellect can be exercised concerning intelligible objects only so far as it is perfected by the intelligible species of something; and in that way it understands itself by an intelligible species, as it understands other things: for it is manifest that by knowing the intelligible object it understands also its own act of understanding, and by this act knows the intellectual faculty. But God is a pure act in the order of existence, as also in the order of intelligible objects; therefore He understands Himself through Himself. _______________________