Because, you see, so to understand, manipulate, and dispose the soulless matter, that the art which is stored away in such mechanisms becomes almost like a soul to this material, in all the various ways in which it mocks movement, and figure, and voice, and so on, may be turned into a proof of there being something in man whereby he shows an innate fitness to think out within himself, through the contemplative and inventive faculties, such thoughts, and having prepared such mechanisms in theory, to put them into practice by manual skill, and exhibit in matter the product of his mind. First, for instance, he saw, by dint of thinking, that to produce any sound there is need of some wind; and then, with a view to produce wind in the mechanism, he previously ascertained by a course of reasoning and close observation of the nature of elements, that there is no vacuum at all in the world, but that the lighter is to be considered a vacuum only by comparison with the heavier; seeing that the air itself, taken as a separate subsistence, is crowded quite full. It is by an abuse of language that a jar is said to be “empty”; for when it is empty of any liquid it is none the less, even in this state, full, in the eyes of the experienced. A proof of this is that a jar when put into a pool of water is not immediately filled, but at first floats on the surface, because the air it contains helps to buoy up its rounded sides; till at last the hand of the drawer of the water forces it down to the bottom, and, when there, it takes in water by its neck; during which process it is shown not to have been empty even before the water came; for there is the spectacle of a sort of combat going on in the neck between the two elements, the water being forced by its weight into the interior, and therefore streaming in; the imprisoned air on the other hand being straitened for room by the gush of the water along the neck, and so rushing in the contrary direction; thus the water is checked by the strong current of air, and gurgles and bubbles against it. Men observed this, and devised in accordance with this property of the two elements a way of introducing air to work their mechanism. They made a kind of cavity of some hard stuff, and prevented the air in it from escaping in any direction; and then introduced water into this cavity through its mouth, apportioning the quantity of water according to requirement; next they allowed an exit in the opposite direction to the air, so that it passed into a pipe placed ready to hand, and in so doing, being violently constrained by the water, became a blast; and this, playing on the structure of the pipe, produced a note. Is it not clearly proved by such visible results that there is a mind of some kind in man, something other than that which is visible, which, by virtue of an invisible thinking nature of its own, first prepares by inward invention such devices, and then, when they have been so matured, brings them to the light and exhibits them in the subservient matter? For if it were possible to ascribe such wonders, as the theory of our opponents does, to the actual constitution of the elements, we should have these mechanisms building themselves spontaneously; the bronze would not wait for the artist, to be made into the likeness of a man, but would become such by an innate force; the air would not require the pipe, to make a note, but would sound spontaneously by its own fortuitous flux and motion; and the jet of the water upwards would not be, as it now is, the result of an artificial pressure forcing it to move in an unnatural direction, but the water would rise into the mechanism of its own accord, finding in that direction a natural channel. But if none of these results are produced spontaneously by elemental force, but, on the contrary, each element is employed at will by artifice; and if artifice is a kind of movement and activity of mind, will not the very consequences of what has been urged by way of objection show us Mind as something other than the thing perceived?
That the thing perceived, I replied, is not the same as the thing not perceived, I grant; but I do not discover any answer to our question in such a statement; it is not yet clear to me what we are to think that thing not-perceived to be; all I have been shown by your argument is that it is not anything material; and I do not yet know the fitting name for it. I wanted especially to know what it is, not what it is not.
We do learn, she replied, much about many things by this very same method, inasmuch as, in the very act of saying a thing is “not so and so,” we by implication interpret the very nature of the thing in question. For instance, when we say a “guileless,” we indicate a good man; when we say “unmanly,” we have expressed that a man is a coward; and it is possible to suggest a great many things in like fashion, wherein we either convey the idea of goodness by the negation of badness, or vice versâ. Well, then, if one thinks so with regard to the matter now before us, one will not fail to gain a proper conception of it. The question is—What are we to think of Mind in its very essence? Now granted that the inquirer has had his doubts set at rest as to the existence of the thing in question, owing to the activities which it displays to us, and only wants to know what it is, he will have adequately discovered it by being told that it is not that which our senses perceive, neither a colour, nor a form, nor a hardness, nor a weight, nor a quantity, nor a cubic dimension, nor a point, nor anything else perceptible in matter; supposing, that is, that there does exist a something beyond all these.
Here I interrupted her discourse: If you leave all these out of the account I do not see how you can possibly avoid cancelling along with them the very thing which you are in search of. I cannot at present conceive to what, as apart from these, the perceptive activity is to cling. For on all occasions in investigating with the scrutinizing intellect the contents of the world, we must, so far as we put our hand at all on what we are seeking, inevitably touch, as blind men feeling along the walls for the door, some one of those things aforesaid; we must come on colour, or form, or quantity, or something else on your list; and when it comes to saying that the thing is none of them, our feebleness of mind induces us to suppose that it does not exist at all.
Shame on such absurdity! said she, indignantly interrupting. A fine conclusion this narrow-minded, grovelling view of the world brings us to! If all that is not cognizable by sense is to be wiped out of existence, the all-embracing Power that presides over things is admitted by this same assertion not to be; once a man has been told about the non-material and invisible nature of the Deity, he must perforce with such a premise reckon it as absolutely non-existent. If, on the other hand, the absence of such characteristics in His case does not constitute any limitation of His existence, how can the Mind of man be squeezed out of existence along with this withdrawal one by one of each property of matter?
Well, then, I retorted, we only exchange one paradox for another by arguing in this way; for our reason will be reduced to the conclusion that the Deity and the Mind of man are identical, if it be true that neither can be thought of, except by the withdrawal of all the data of sense.
Source: On the Soul and the Resurrection (New Advent)