Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
After considering the knowledge of God, it remains to consider ideas. And about this there are three points of inquiry:
(1) Whether there are ideas?
(2) Whether they are many, or one only?
(3) Whether there are ideas of all things known by God?
Objection 1: It seems that there are no ideas. For Dionysius says (Div. Nom. vii), that God does not know things by ideas. But ideas are for nothing else except that things may be known through them. Therefore there are no ideas.
Objection 2: Further, God knows all things in Himself, as has been already said (Q[14], A[5]). But He does not know Himself through an idea; neither therefore other things.
Objection 3: Further, an idea is considered to be the principle of knowledge and action. But the divine essence is a sufficient principle of knowing and effecting all things. It is not therefore necessary to suppose ideas.
On the contrary, Augustine says (Octog. Tri. Quaest. qu. xlvi),"Such is the power inherent in ideas, that no one can be wise unless they are understood."
I answer that, It is necessary to suppose ideas in the divine mind. For the Greek word is in Latin "forma." Hence by ideas are understood the forms of things, existing apart from the things themselves. Now the form of anything existing apart from the thing itself can be for one of two ends: either to be the type of that of which it is called the form, or to be the principle of the knowledge of that thing, inasmuch as the forms of things knowable are said to be in him who knows them. In either case we must suppose ideas, as is clear for the following reason:
In all things not generated by chance, the form must be the end of any generation whatsoever. But an agent does not act on account of the form, except in so far as the likeness of the form is in the agent, as may happen in two ways. For in some agents the form of the thing to be made pre-exists according to its natural being, as in those that act by their nature; as a man generates a man, or fire generates fire. Whereas in other agents (the form of the thing to be made pre-exists) according to intelligible being, as in those that act by the intellect; and thus the likeness of a house pre-exists in the mind of the builder. And this may be called the idea of the house, since the builder intends to build his house like to the form conceived in his mind. As then the world was not made by chance, but by God acting by His intellect, as will appear later (Q[46], A[1]), there must exist in the divine mind a form to the likeness of which the world was made. And in this the notion of an idea consists.
Reply to Objection 1: God does not understand things according to an idea existing outside Himself. Thus Aristotle (Metaph. ix) rejects the opinion of Plato, who held that ideas existed of themselves, and not in the intellect.
Reply to Objection 2: Although God knows Himself and all else by His own essence, yet His essence is the operative principle of all things, except of Himself. It has therefore the nature of an idea with respect to other things; though not with respect to Himself.
Reply to Objection 3: God is the similitude of all things according to His essence; therefore an idea in God is identical with His essence.
Objection 1: It seems that ideas are not many. For an idea in God is His essence. But God's essence is one only. Therefore there is only one idea.
Objection 2: Further, as the idea is the principle of knowing and operating, so are art and wisdom. But in God there are not several arts or wisdoms. Therefore in Him there is no plurality of ideas.
Objection 3: Further, if it be said that ideas are multiplied according to their relations to different creatures, it may be argued on the contrary that the plurality of ideas is eternal. If, then, ideas are many, but creatures temporal, then the temporal must be the cause of the eternal.
Objection 4: Further, these relations are either real in creatures only, or in God also. If in creatures only, since creatures are not from eternity, the plurality of ideas cannot be from eternity, if ideas are multiplied only according to these relations. But if they are real in God, it follows that there is a real plurality in God other than the plurality of Persons: and this is against the teaching of Damascene (De Fide Orth. i, 10), who says, in God all things are one, except "ingenerability, generation, and procession." Ideas therefore are not many.
On the contrary, Augustine says (Octog. Tri. Quaest. qu. xlvi), "Ideas are certain principal forms, or permanent and immutable types of things, they themselves not being formed. Thus they are eternal, and existing always in the same manner, as being contained in the divine intelligence. Whilst, however, they themselves neither come into being nor decay, yet we say that in accordance with them everything is formed that can rise or decay, and all that actually does so."
I answer that, It must necessarily be held that ideas are many. In proof of which it is to be considered that in every effect the ultimate end is the proper intention of the principal agent, as the order of an army (is the proper intention) of the general. Now the highest good existing in things is the good of the order of the universe, as the Philosopher clearly teaches in Metaph. xii. Therefore the order of the universe is properly intended by God, and is not the accidental result of a succession of agents, as has been supposed by those who have taught that God created only the first creature, and that this creature created the second creature, and so on, until this great multitude of beings was produced. According to this opinion God would have the idea of the first created thing alone; whereas, if the order itself of the universe was created by Him immediately, and intended by Him, He must have the idea of the order of the universe. Now there cannot be an idea of any whole, unless particular ideas are had of those parts of which the whole is made; just as a builder cannot conceive the idea of a house unless he has the idea of each of its parts. So, then, it must needs be that in the divine mind there are the proper ideas of all things. Hence Augustine says (Octog. Tri. Quaest. qu. xlvi), "that each thing was created by God according to the idea proper to it," from which it follows that in the divine mind ideas are many. Now it can easily be seen how this is not repugnant to the simplicity of God, if we consider that the idea of a work is in the mind of the operator as that which is understood, and not as the image whereby he understands, which is a form that makes the intellect in act. For the form of the house in the mind of the builder, is something understood by him, to the likeness of which he forms the house in matter. Now, it is not repugnant to the simplicity of the divine mind that it understand many things; though it would be repugnant to its simplicity were His understanding to be formed by a plurality of images. Hence many ideas exist in the divine mind, as things understood by it; as can be proved thus. Inasmuch as He knows His own essence perfectly, He knows it according to every mode in which it can be known. Now it can be known not only as it is in itself, but as it can be participated in by creatures according to some degree of likeness. But every creature has its own proper species, according to which it participates in some degree in likeness to the divine essence. So far, therefore, as God knows His essence as capable of such imitation by any creature, He knows it as the particular type and idea of that creature; and in like manner as regards other creatures. So it is clear that God understands many particular types of things and these are many ideas.
Reply to Objection 1: The divine essence is not called an idea in so far as it is that essence, but only in so far as it is the likeness or type of this or that thing. Hence ideas are said to be many, inasmuch as many types are understood through the self-same essence.
Reply to Objection 2: By wisdom and art we signify that by which God understands; but an idea, that which God understands. For God by one understands many things, and that not only according to what they are in themselves, but also according as they are understood, and this is to understand the several types of things. In the same way, an architect is said to understand a house, when he understands the form of the house in matter. But if he understands the form of a house, as devised by himself, from the fact that he understands that he understands it, he thereby understands the type or idea of the house. Now not only does God understand many things by His essence, but He also understands that He understands many things by His essence. And this means that He understands the several types of things; or that many ideas are in His intellect as understood by Him.
Reply to Objection 3: Such relations, whereby ideas are multiplied, are caused not by the things themselves, but by the divine intellect comparing its own essence with these things.
Reply to Objection 4: Relations multiplying ideas do not exist in created things, but in God. Yet they are not real relations, such as those whereby the Persons are distinguished, but relations understood by God.
Objection 1: It seems that there are not ideas in God of all things that He knows. For the idea of evil is not in God; since it would follow that evil was in Him. But evil things are known by God. Therefore there are not ideas of all things that God knows.
Objection 2: Further, God knows things that neither are, nor will be, nor have been, as has been said above (A[9]). But of such things there are no ideas, since, as Dionysius says (Div. Nom. v): "Acts of the divine will are the determining and effective types of things." Therefore there are not in God ideas of all things known by Him.
Objection 3: Further, God knows primary matter, of which there can be no idea, since it has no form. Hence the same conclusion.
Objection 4: Further, it is certain that God knows not only species, but also genera, singulars, and accidents. But there are not ideas of these, according to Plato's teaching, who first taught ideas, as Augustine says (Octog. Tri. Quaest. qu. xlvi). Therefore there are not ideas in God of all things known by Him.
On the contrary, Ideas are types existing in the divine mind, as is clear from Augustine (Octog. Tri. Quaest. qu. xlvi). But God has the proper types of all things that He knows; and therefore He has ideas of all things known by Him.
I answer that, As ideas, according to Plato, are principles of the knowledge of things and of their generation, an idea has this twofold office, as it exists in the mind of God. So far as the idea is the principle of the making of things, it may be called an "exemplar," and belongs to practical knowledge. But so far as it is a principle of knowledge, it is properly called a "type," and may belong to speculative knowledge also. As an exemplar, therefore, it has respect to everything made by God in any period of time; whereas as a principle of knowledge it has respect to all things known by God, even though they never come to be in time; and to all things that He knows according to their proper type, in so far as they are known by Him in a speculative manner.
Reply to Objection 1: Evil is known by God not through its own type, but through the type of good. Evil, therefore, has no idea in God, neither in so far as an idea is an "exemplar" nor as a "type."
Reply to Objection 2: God has no practical knowledge, except virtually, of things which neither are, nor will be, nor have been. Hence, with respect to these there is no idea in God in so far as idea signifies an "exemplar" but only in so far as it denotes a "type."
Reply to Objection 3: Plato is said by some to have considered matter as not created; and therefore he postulated not an idea of matter but a concause with matter. Since, however, we hold matter to be created by God, though not apart from form, matter has its idea in God; but not apart from the idea of the composite; for matter in itself can neither exist, nor be known.
Reply to Objection 4: Genus can have no idea apart from the idea of species, in so far as idea denotes an "exemplar"; for genus cannot exist except in some species. The same is the case with those accidents that inseparably accompany their subject; for these come into being along with their subject. But accidents which supervene to the subject, have their special idea. For an architect produces through the form of the house all the accidents that originally accompany it; whereas those that are superadded to the house when completed, such as painting, or any other such thing, are produced through some other form. Now individual things, according to Plato, have no other idea than that of species; both because particular things are individualized by matter, which, as some say, he held to be uncreated and the concause with the idea; and because the intention of nature regards the species, and produces individuals only that in them the species may be preserved. However, divine providence extends not merely to species; but to individuals as will be shown later (Q[22], A[3] ).