That the Truths which we confess concerning God fall under two Modes or Categories

BECAUSE not every truth admits of the same mode of manifestation, and "a well-educated man will expect exactness in every class of subject, according as the nature of the thing admits," as is very well remarked by the Philosopher (Eth. Nicom. I, 1094b), we must first show what mode of proof is possible for the truth that we have now before us. The truths that we confess concerning God fall under two modes. Some things true of God are beyond all the competence of human reason, as that God is Three and One. Other things there are to which even human reason can attain, as the existence and unity of God, which philosophers have proved to a demonstration under the guidance of the light of natural reason. That there are points of absolute intelligibility in God altogether beyond the compass of human reason, most manifestly appears. For since the leading principle of all knowledge of any given subject-matter is an understanding of the thing's innermost being, or substance -- according to the doctrine of the Philosopher, that the essence is the principle of demonstration -- it follows that the mode of our knowledge of the substance must be the mode of knowledge of whatever we know about the substance. Hence if the human understanding comprehends the substance of anything, as of a stone or triangle, none of the points of intelligibility about that thing will exceed the capacity of human reason.* But this is not our case with regard to God. The human understanding cannot go so far of its natural power as to grasp His substance, since under the conditions of the present life the knowledge of our understanding commences with sense; and therefore objects beyond sense cannot be grasped by human understanding except so far as knowledge is gathered of them through the senses. But things of sense cannot lead our understanding to read in them the essence of the Divine Substance, inasmuch as they are effects inadequate to the power that caused them. Nevertheless our understanding is thereby led to some knowledge of God, namely, of His existence and of other attributes that must necessarily be attributed to the First Cause. There are, therefore, some points of intelligibility in God, accessible to human reason, and other points that altogether transcend the power of human reason.*

The same thing may be understood from consideration of degrees of intelligibility.* Of two minds, one of which has a keener insight into truth than the other, the higher mind understands much that the other cannot grasp at all, as is clear in the 'plain man' (in rustico), who can in no way grasp the subtle theories of philosophy. Now the intellect of an angel excels that of a man more than the intellect of the ablest philosopher excels that of the plainest of plain men (rudissimi idiotae). The angel has a higher standpoint in creation than man as a basis of his knowledge of God, inasmuch as the substance of the angel, whereby he is led to know God by a process of natural knowledge, is nobler and more excellent than the things of sense, and even than the soul itself, whereby the human mind rises to the knowledge of God. But the Divine Mind exceeds the angelic much more than the angelic the human. For the Divine Mind of its own comprehensiveness covers the whole extent of its substance, and therefore perfectly understands its own essence, and knows all that is knowable about itself; but an angel of his natural knowledge does not know the essence of God, because the angel's own substance, whereby it is led to a knowledge of God, is an effect inadequate to the power of the cause that created it. Hence not all things that God understands in Himself can be grasped by the natural knowledge of an angel; nor is human reason competent to take in all that an angel understands of his own natural ability. As therefore it would be the height of madness in a 'plain man' to declare a philosopher's propositions false, because he could not understand them, so and much more would a man show exceeding folly if he suspected of falsehood a divine revelation given by the ministry of angels, on the mere ground that it was beyond the investigation of reason.*

The same thing manifestly appears from the incapacity which we daily experience in the observation of nature. We are ignorant of very many properties of the things of sense; and of the properties that our senses do apprehend, in most cases we cannot perfectly discover the reason. Much more is it beyond the competence of human reason to investigate all the points of intelligibility in that supreme excellent and transcendent substance of God. Consonant with this is the saying of the Philosopher, that "as the eyes of bats are to the light of the sun, so is the intelligence of our soul to the things most manifest by nature" (Aristotle, Metaphysics I, min. i). To this truth Holy Scripture also bears testimony. For it is said: Perchance thou wilt seize upon the traces of God, and fully discover the Almighty (Job xi, 7). And, Lo, God is great, and surpassing our knowledge (Job xxxvi, 26). And, We know in part (I Cor. xiii, 9). Not everything, therefore, that is said of God, even though it be beyond the power of reason to investigate, is at once to be rejected as false.

1.2 : Of the Author's Purpose
1.4 : That it is an Advantage for the Truths of God, known by Natural Reason, to be proposed to men to be believed on Faith