23 To this most wholesome humility, in which our Lord Jesus Christ is our teacher— having submitted to humiliation that He might instruct us in this— to this humility, I say, the most formidable adversary is a certain kind of most unenlightened knowledge, if I may so call it, in which we congratulate ourselves on knowing what may have been the views of Anaximenes, Anaxagoras, Pythagoras, Democritus, and others of the same kind, imagining that by this we become learned men and scholars, although such attainments are far removed from true learning and erudition. For the man who has learned that God is not extended or diffused through space, either finite or infinite, so as to be greater in one part and less in another, but that He is wholly present everywhere, as the Truth is, of which no one in his senses will affirm that it is partly in one place, partly in another— and the Truth is God Himself— such a man will not be moved by the opinions of any philosopher soever who believes [like Anaximenes] that the infinite air around us is the true God. What matters it to such a man though he be ignorant what bodily form they speak of, since they speak of a form which is bounded on all sides? What matters it to him whether it was only as an Academician, and merely for the purpose of confuting Anaximenes, who had said that God is a material existence—for air is material—that Cicero objected that God must have form and beauty? or himself perceived that truth has immaterial form and beauty, by which the mind itself is moulded, and by which we judge all the deeds of the wise man to be beautiful, and therefore affirmed that God must be of the most perfect beauty, not merely for the purpose of confuting an antagonist, but with profound insight into the fact that nothing is more beautiful than truth itself, which is cognisable by the understanding alone, and is immutable? Moreover, as to the opinion of Anaximenes, who held that the air is generated, and at the same time believed it to be God, it does not in the least move the man who understands that, since the air is certainly not God, there is no likeness between the manner in which the air is generated, that is to say, produced by some cause, and the manner, understood by none except through divine inspiration, in which He was begotten who is the Word of God, God with God. Moreover, who does not see that even in regard to material things he speaks most foolishly in affirming that air is generated, and is at the same time God, while he refuses to give the name of God to that by which the air has been generated—for it is impossible that it could be generated by no power? Yet once more, his saying that the air is always in motion will have no disturbing influence as proof that the air is God upon the man who knows that all movements of body are of a lower order than movements of the soul, but that even the movements of the soul are infinitely slow compared with His who is supreme and immutable Wisdom.
24. In like manner, if Anaxagoras or any other affirm that the mind is essential truth and wisdom, what call have I to debate with a man about a word? For it is manifest that mind gives being to the order and mode of all things, and that it may be suitably called infinite with respect not to its extension in space, but to its power, the range of which transcends all human thought. Nor [shall I dispute his assertion] that this essential wisdom is formless; for this is a property of material things, that whatever bodies are infinite are also formless. Cicero, however, from his desire to confute such opinions, as I suppose, in contending with adversaries who believed in nothing immaterial, denies that anything can be annexed to that which is infinite, because in things material there must be a boundary at the part to which anything is annexed. Therefore he says that Anaxagoras “did not see that motion joined to sensation and to it” (i.e. linked to it in unbroken connection) “is impossible in the infinite” (that is, in a substance which is infinite), as if treating of material substances, to which nothing can be joined except at their boundaries. Moreover, in the succeeding words— “and that sensation of which the whole system of nature is not sensible when struck is an impossibility” — Cicero speaks as if Anaxagoras had said that mind— to which he ascribed the power of ordering and fashioning all things— had sensation such as the soul has by means of the body. For it is manifest that the whole soul has sensation when it feels anything by means of the body; for whatever is perceived by sensation is not concealed from the whole soul. Now, Cicero's design in saying that the whole system of nature must be conscious of every sensation was, that he might, as it were, take from the philosopher that mind which he affirms to be infinite. For how does the whole of nature experience sensation if it be infinite? Bodily sensation begins at some point, and does not pervade the whole of any substance unless it be one in which it can reach an end; but this, of course, cannot be said of that which is infinite. Anaxagoras, however had not said anything about bodily sensation. The word “whole,” moreover, is used differently when we speak of that which is immaterial, because it is understood to be without boundaries in space, so that it may be spoken of as a whole and at the same time as infinite— the former because of its completeness, the latter because of its not being limited by boundaries in space.
25. “Furthermore,” says Cicero, “if he will affirm that the mind itself is, so to speak, some kind of animal, there must be some principle from within from which it receives the name 'animal,'”— so that mind, according to Anaxagoras, is a kind of body, and has within it an animating principle, because of which it is called “animal.” Observe how he speaks in language which we are accustomed to apply to things corporeal—animals being in the ordinary sense of the word visible substances,— adapting himself, as I suppose, to the blunted perceptions of those against whom he argues; and yet he has uttered a thing which, if they could awake to perceive it, might suffice to teach them that everything which presents itself to our minds as a living body must be thought of not as itself a soul, but as an animal having a soul. For having said, “There must be something within from which it receives the name animal,” he adds, “But what is deeper within than mind?” The mind, therefore, cannot have any inner soul, by possessing which it is an animal; for it is itself that which is innermost. If, then, it is an animal, let it have some external body in relation to which it may be within; for this is what he means by saying, “It is therefore girt round by an exterior body,” as if Anaxagoras had said that mind cannot be otherwise than as belonging to some animal. And yet Anaxagoras held the opinion that essential supreme Wisdom is mind, although it is not the peculiar property of any living being, so to speak, since Truth is near to all souls alike that are able to enjoy it. Observe, therefore, how wittily he concludes the argument: “Since this is not the opinion of Anaxagoras” (i.e. seeing that he does not hold that that mind which he calls God is girt about with an external body, through its relation to which it could be an animal), “we must say that mind pure and simple, without the addition of anything” (i.e. of any body) “through which it may exercise sensation, seems to be beyond the range and conceptions of our intelligence.”
Source: Letters (New Advent)