On The Holy Trinity by St. Augustine
Chapter 4.--How This Unity Comes to Pass.
7. But if that will which moves to and fro, hither and thither, the eye that is to be informed, and unites it when formed, shall have wholly converged to the inward phantasy, and shall have absolutely turned the mind's eye from the presence of the bodies which lie around the senses, and from the very bodily senses themselves, and shall have wholly turned it to that image, which is perceived within; then so exact a likeness of the bodily species expressed from the memory is presented, that not even reason itself is permitted to discern whether the body itself is seen without, or only something of the kind thought of within. For men sometimes either allured or frightened by over-much thinking of visible things, have even suddenly uttered words accordingly, as if in real fact they were engaged in the very midst of such actions or sufferings. And I remember some one telling me that he was wont to perceive in thought, so distinct and as it were solid, a form of a female body, as to be moved, as though it were a reality. Such power has the soul over its own body, and such influence has it in turning and changing the quality of its [corporeal] garment; just as a man may be affected when clothed, to whom his clothing sticks. It is the same kind of affection, too, with which we are beguiled through imaginations in sleep. But it makes a very great difference, whether the senses of the body are lulled to torpor, as in the case of sleepers, or disturbed from their inward structure, as in the case of madmen, or distracted in some other mode, as in that of diviners or prophets; and so from one or other of these causes, the intention of the mind is forced by a kind of necessity upon those images which occur to it, either from memory, or by some other hidden force through certain spiritual commixtures of a similarly spiritual substance: or whether, as sometimes happens to people in health and awake, that the will occupied by thought turns itself away from the senses, and so informs the eye of the mind by various images of sensible things, as though those sensible things themselves were actually perceived. But these impressions of images not only take place when the will is directed upon such things by desiring them, but also when, in order to avoid and guard against them, the mind is carried away to look upon these very thing so as to flee from them. And hence, not only desire, but fear, causes both the bodily eye to be informed by the sensible things themselves, and the mental eye (acies) by the images of those sensible things. Accordingly, the more vehement has been either fear or desire, the more distinctly is the eye informed, whether in the case of him who [sensuously] perceives by means of the body that which lies close to him in place, or in the case of him who conceives from the image of the body which is contained in the memory. What then a body in place is to the bodily sense, that, the similitude of a body in memory is to the eye of the mind; and what the vision of one who looks at a thing is to that appearance of the body from which the sense is informed, that, the vision of a concipient is to the image of the body established in the memory, from which the eye of the mind is informed; and what the intention of the will is towards a body seen and the vision to be combined with it, in order that a certain unity of three things may therein take place, although their nature is diverse, that, the same intention of the will is towards combining the image of the body which is in the memory, and the vision of the concipient, that is, the form which the eye of the mind has taken in returning to the memory, in order that here too a certain unity may take place of three things, not now distinguished by diversity of nature, but of one and the same substance; because this whole is within, and the whole is one mind.