On The Holy Trinity by St. Augustine
Chapter 5.--Why the Soul is Enjoined to Know Itself. Whence Come the Errors of the Mind Concerning Its Own Substance.
7. Why therefore is it enjoined upon it, that it should know itself? I suppose, in order that, it may consider itself, and live according to its own nature; that is, seek to be regulated according to its own nature, viz., under Him to whom it ought to be subject, and above those things to which it is to be preferred; under Him by whom it ought to be ruled, above those things which it ought to rule. For it does many things through vicious desire, as though in forgetfulness of itself. For it sees some things intrinsically excellent, in that more excellent nature which is God: and whereas it ought to remain steadfast that it may enjoy them, it is turned away from Him, by wishing to appropriate those things to itself, and not to be like to Him by His gift, but to be what He is by its own, and it begins to move and slip gradually down into less and less, which it thinks to be more and more; for it is neither sufficient for itself, nor is anything at all sufficient for it, if it withdraw from Him who is alone sufficient: and so through want and distress it becomes too intent upon its own actions and upon the unquiet delights which it obtains through them: and thus, by the desire of acquiring knowledge from those things that are without, the nature of which it knows and loves, and which it feels can be lost unless held fast with anxious care, it loses its security, and thinks of itself so much the less, in proportion as it feels the more secure that it cannot lose itself. So, whereas it is one thing not to know oneself, and another not to think of oneself (for we do not say of the man that is skilled in much learning, that he is ignorant of grammar, when he is only not thinking of it, because he is thinking at the time of the art of medicine); -- whereas, then, I say it is one thing not to know oneself, and another not to think of oneself, such is the strength of love, that the mind draws in with itself those things which it has long thought of with love, and has grown into them by the close adherence of diligent study, even when it returns in some way to think of itself. And because these things are corporeal which it loved externally through the carnal senses; and because it has become entangled with them by a kind of daily familiarity, and yet cannot carry those corporeal things themselves with itself internally as it were into the region of incorporeal nature; therefore it combines certain images of them, and thrusts them thus made from itself into itself. For it gives to the forming of them somewhat of its own substance, yet preserves the while something by which it may judge freely of the species of those images; and this something is more properly the mind, that is, the rational understanding, which is preserved that it may judge. For we see that we have those parts of the soul which are informed by the likenesses of corporeal things, in common also with beasts.