26 Nothing is more certain than that this lies beyond the range and conception of the intelligence of Stoics and Epicureans, who cannot think of anything which is not material. But by the word “our” intelligence he means “human” intelligence; and he very properly does not say, “it lies beyond our intelligence,” but “it seems to lie beyond.” For their opinion is, that this lies beyond the understanding of all men, and therefore they think that nothing of the kind can be. But there are some whose intelligence apprehends, in so far as this is given to man, the fact that there is pure and simple Wisdom and Truth, which is the peculiar property of no living being, but which imparts wisdom and truth to all souls alike which are susceptible of its influence. If Anaxagoras perceived the existence of this supreme Wisdom, and apprehended it to be God, and called it Mind, it is not by the mere name of this philosopher— with whom, on account of his place in the remote antiquity of erudition, all raw recruits in literature (to adopt a military phrase) delight to boast an acquaintance— that we are made learned and wise; nor is it even by our having the knowledge through which he knew this truth. For truth ought to be dear to me not merely because it was not unknown to Anaxagoras, but because, even though none of these philosophers had known it, it is the truth.
27. If, therefore, it is unbecoming for us to be elated either by the knowledge of the man who perhaps apprehended the truth, by which knowledge we obtain, as it were, the appearance of learning, or even by the solid possession of the truth itself, whereby we obtain real acquisitions in learning, how much less can the names and tenets of those men who were in error assist us in Christian learning and in making known things obscure? For if we be men, it would be more fitting that we should grieve on account of the errors into which so many famous men fell, if we happen to hear of them, than that we should studiously investigate them, in order that, among men who are ignorant of them, we may enjoy the gratification of a most contemptible conceit of knowledge. For how much better would it be that I should never have heard the name of Democritus, than that I should now with sorrow ponder the fact that a man was highly esteemed in his own age who thought that the gods were images which emanated from solid bodies, but were not solid themselves; and that these, circling this way and that way by their independent motion, and gliding into the minds of men, make the divine power enter into the region of their thoughts, although, certainly, that body from which the image emanated may be rightly judged to surpass the image in excellence and proportion, as it surpasses it in solidity. Hence his opinion wavered, as they say, and oscillated, so that sometimes he said that the deity was some kind of nature from which images emanate, and which nevertheless can be thought of only by means of those images which he pours forth and sends out, that is, which from that nature (which he considered to be something material and eternal, and on this very account divine) were borne as by a kind of evaporation or continuous emanation, and came and entered into our minds, so that we could form the thought of a god or gods. For these philosophers conceive of no cause of thought in our minds, except when images from those bodies which are the object of our thoughts come and enter into our minds; as if, forsooth, there were not many things, yea, more than we can number, which, without any material form, and yet intelligible, are apprehended by those who know how to apprehend such things. Take as an example essential Wisdom and Truth, of which if they can frame no idea, I wonder why they dispute concerning it at all; if, however, they do frame some idea of it in thought, I wish they would tell me either from what body the image of truth comes into their minds, or of what kind it is.
28. Democritus, however, is said to differ here also in his doctrine on physics from Epicurus; for he holds that there is in the concourse of atoms a certain vital and breathing power, by which power (I believe) he affirms that the images themselves (not all images of all things, but images of the gods) are endued with divine attributes, and that the first beginnings of the mind are in those universal elements to which he ascribed divinity, and that the images possess life, inasmuch as they are wont either to benefit or to hurt us. Epicurus, however, does not assume anything in the first beginnings of things but atoms, that is, certain corpuscles, so minute that they cannot be divided or perceived either by sight or by touch; and his doctrine is, that by the fortuitous concourse (clashing) of these atoms, existence is given both to innumerable worlds and to living things, and to the souls which animate them, and to the gods whom, in human form, he has located, not in any world, but outside of the worlds, and in the spaces which separate them; and he will not allow of any object of thought beyond things material. But in order to these becoming an object of thought, he says that from those things which he represents as formed of atoms, images more subtle than those which come to our eyes flow down and enter into the mind. For according to him, the cause of our seeing is to be found in certain images so huge that they embrace the whole outer world. But I suppose that you already understand their opinions regarding these images.
29. I wonder that Democritus was not convinced of the error of his philosophy even by this fact, that such huge images coming into our minds, which are so small (if being, as they affirm, material, the soul is confined within the body's dimensions), could not possibly, in the entirety of their size, come into contact with it. For when a small body is brought into contact with a large one, it cannot in any wise be touched at the same moment by all points of the larger. How, then, are these images at the same moment in their whole extent objects of thought, if they become objects of thought only in so far as, coming and entering into the mind, they touch it, seeing that they cannot in their whole extent either find entrance into so small a body or come in contact with so small a mind? Bear in mind, of course, that I am speaking now after their manner; for I do not hold the mind to be such as they affirm. It is true that Epicurus alone can be assailed with this argument, if Democritus holds that the mind is immaterial; but we may ask him in turn why he did not perceive that it is at once unnecessary and impossible for the mind, being immaterial, to think through the approach and contact of material images. Both philosophers alike are certainly confuted by the facts of vision; for images so great cannot possibly touch in their entirety eyes so small.
Source: Letters (New Advent)