Thomas Aquinas, Summa Theologiae

Objection 1: It seems that God does not know things besides Himself. For all other things but God are outside of God. But Augustine says (Octog. Tri. Quaest. qu. xlvi) that "God does not behold anything out of Himself." Therefore He does not know things other than Himself.

Objection 2: Further, the object understood is the perfection of the one who understands. If therefore God understands other things besides Himself, something else will be the perfection of God, and will be nobler than He; which is impossible.

Objection 3: Further, the act of understanding is specified by the intelligible object, as is every other act from its own object. Hence the intellectual act is so much the nobler, the nobler the object understood. But God is His own intellectual act. If therefore God understands anything other than Himself, then God Himself is specified by something else than Himself; which cannot be. Therefore He does not understand things other than Himself.

On the contrary, It is written: "All things are naked and open to His eyes" (Heb. 4:13).

I answer that, God necessarily knows things other than Himself. For it is manifest that He perfectly understands Himself; otherwise His existence would not be perfect, since His existence is His act of understanding. Now if anything is perfectly known, it follows of necessity that its power is perfectly known. But the power of anything can be perfectly known only by knowing to what its power extends. Since therefore the divine power extends to other things by the very fact that it is the first effective cause of all things, as is clear from the aforesaid (Question 2, Article 3), God must necessarily know things other than Himself. And this appears still more plainly if we add that the every existence of the first effective cause---viz. God---is His own act of understanding. Hence whatever effects pre-exist in God, as in the first cause, must be in His act of understanding, and all things must be in Him according to an intelligible mode: for everything which is in another, is in it according to the mode of that in which it is.

Now in order to know how God knows things other than Himself, we must consider that a thing is known in two ways: in itself, and in another. A thing is known in itself when it is known by the proper species adequate to the knowable object; as when the eye sees a man through the image of a man. A thing is seen in another through the image of that which contains it; as when a part is seen in the whole by the image of the whole; or when a man is seen in a mirror by the image in the mirror, or by any other mode by which one thing is seen in another.

So we say that God sees Himself in Himself, because He sees Himself through His essence; and He sees other things not in themselves, but in Himself; inasmuch as His essence contains the similitude of things other than Himself.

Reply to Objection 1: The passage of Augustine in which it is said that God "sees nothing outside Himself" is not to be taken in such a way, as if God saw nothing outside Himself, but in the sense that what is outside Himself He does not see except in Himself, as above explained.

Reply to Objection 2: The object understood is a perfection of the one understanding not by its substance, but by its image, according to which it is in the intellect, as its form and perfection, as is said in De Anima iii. For "a stone is not in the soul, but its image." Now those things which are other than God are understood by God, inasmuch as the essence of God contains their images as above explained; hence it does not follow that there is any perfection in the divine intellect other than the divine essence.

Reply to Objection 3: The intellectual act is not specified by what is understood in another, but by the principal object understood in which other things are understood. For the intellectual act is specified by its object, inasmuch as the intelligible form is the principle of the intellectual operation: since every operation is specified by the form which is its principle of operation; as heating by heat. Hence the intellectual operation is specified by that intelligible form which makes the intellect in act. And this is the image of the principal thing understood, which in God is nothing but His own essence in which all images of things are comprehended. Hence it does not follow that the divine intellectual act, or rather God Himself, is specified by anything else than the divine essence itself.

Articulus 5

Argumentum 1

Ad quintum sic proceditur. Videtur quod deus non cognoscat alia a se. Quaecumque enim sunt alia a deo, sunt extra ipsum.

Sed Augustinus dicit, in libro octoginta trium qu., quod neque quidquam deus extra seipsum intuetur.

Ergo non cognoscit alia a se.

Argumentum 2

Praeterea, intellectum est perfectio intelligentis. Si ergo deus intelligat alia a se, aliquid aliud erit perfectio dei, et nobilius ipso. Quod est impossibile.

Argumentum 3

Praeterea, ipsum intelligere speciem habet ab intelligibili, sicut et omnis alius actus a suo obiecto, unde et ipsum intelligere tanto est nobilius, quanto etiam nobilius est ipsum quod intelligitur. Sed deus est ipsum suum intelligere, ut ex dictis patet.

Si igitur deus intelligit aliquid aliud a se, ipse deus specificatur per aliquid aliud a se, quod est impossibile. Non igitur intelligit alia a se.

Sed Contra

Sed contra est quod dicitur Hebr. IV, omnia nuda et aperta sunt oculis eius.

Corpus

Respondeo dicendum quod necesse est deum cognoscere alia a se.

Manifestum est enim quod seipsum perfecte intelligit, alioquin suum esse non esset perfectum, cum suum esse sit suum intelligere.

Si autem perfecte aliquid cognoscitur, necesse est quod virtus eius perfecte cognoscatur. Virtus autem alicuius rei perfecte cognosci non potest, nisi cognoscantur ea ad quae virtus se extendit. Unde, cum virtus divina se extendat ad alia, eo quod ipsa est prima causa effectiva omnium entium, ut ex supradictis patet; necesse est quod deus alia a se cognoscat. Et hoc etiam evidentius fit, si adiungatur quod ipsum esse causae agentis primae, scilicet dei, est eius intelligere. Unde quicumque effectus praeexistunt in deo sicut in causa prima, necesse est quod sint in ipso eius intelligere; et quod omnia in eo sint secundum modum intelligibilem, nam omne quod est in altero, est in eo secundum modum eius in quo est.

Ad sciendum autem qualiter alia a se cognoscat, considerandum est quod dupliciter aliquid cognoscitur, uno modo, in seipso; alio modo, in altero. In seipso quidem cognoscitur aliquid, quando cognoscitur per speciem propriam adaequatam ipsi cognoscibili, sicut cum oculus videt hominem per speciem hominis. In alio autem videtur id quod videtur per speciem continentis, sicut cum pars videtur in toto per speciem totius, vel cum homo videtur in speculo per speciem speculi, vel quocumque alio modo contingat aliquid in alio videri. Sic igitur dicendum est quod deus seipsum videt in seipso, quia seipsum videt per essentiam suam.

Alia autem a se videt non in ipsis, sed in seipso, inquantum essentia sua continet similitudinem aliorum ab ipso.

Ad 1

Ad primum ergo dicendum quod verbum Augustini dicentis quod deus nihil extra se intuetur, non est sic intelligendum, quasi nihil quod sit extra se intueatur, sed quia id quod est extra seipsum, non intuetur nisi in seipso, ut dictum est.

Ad 2

Ad secundum dicendum quod intellectum est perfectio intelligentis non quidem secundum suam substantiam, sed secundum suam speciem, secundum quam est in intellectu, ut forma et perfectio eius, lapis enim non est in anima, sed species eius, ut dicitur in III de anima.

Ea vero quae sunt alia a deo, intelliguntur a deo inquantum essentia dei continet species eorum, ut dictum est.

Unde non sequitur quod aliquid aliud sit perfectio divini intellectus, quam ipsa essentia dei.

Ad 3

Ad tertium dicendum quod ipsum intelligere non specificatur per id quod in alio intelligitur, sed per principale intellectum, in quo alia intelliguntur. Intantum enim ipsum intelligere specificatur per obiectum suum, inquantum forma intelligibilis est principium intellectualis operationis, nam omnis operatio specificatur per formam quae est principium operationis, sicut calefactio per calorem. Unde per illam formam intelligibilem specificatur intellectualis operatio, quae facit intellectum in actu. Et haec est species principalis intellecti, quae in deo nihil est aliud quam essentia sua, in qua omnes species rerum comprehenduntur. Unde non oportet quod ipsum intelligere divinum, vel potius ipse deus, specificetur per aliud quam per essentiam divinam.