HOW THE SOUL WHILE UNITED TO THE BODY UNDERSTANDS CORPOREAL THINGS BENEATH IT (EIGHT ARTICLES)
We now have to consider the acts of the soul in regard to the intellectual and the appetitive powers: for the other powers of the soul do not come directly under the consideration of the theologian. Furthermore, the acts of the appetitive part of the soul come under the consideration of the science of morals; wherefore we shall treat of them in the second part of this work, to which the consideration of moral matters belongs. But of the acts of the intellectual part we shall treat now.
In treating of these acts we shall proceed in the following order: First, we shall inquire how the soul understands when united to the body; secondly, how it understands when separated therefrom.
The former of these inquiries will be threefold: (1) How the soul understands bodies which are beneath it; (2) How it understands itself and things contained in itself; (3) How it understands immaterial substances, which are above it.
In treating of the knowledge of corporeal things there are three points to be considered: (1) Through what does the soul know them? (2) How and in what order does it know them? (3) What does it know in them?
Under the first head there are eight points of inquiry:
(1) Whether the soul knows bodies through the intellect?
(2) Whether it understands them through its essence, or through any species?
(3) If through some species, whether the species of all things intelligible are naturally innate in the soul?
(4) Whether these species are derived by the soul from certain separate immaterial forms?
(5) Whether our soul sees in the eternal ideas all that it understands?
(6) Whether it acquires intellectual knowledge from the senses?
(7) Whether the intellect can, through the species of which it is possessed, actually understand, without turning to the phantasms?
(8) Whether the judgment of the intellect is hindered by an obstacle in the sensitive powers?
Whether the soul knows bodies through the intellect?
Objection 1: It would seem that the soul does not know bodies through the intellect. For Augustine says (Soliloq. ii, 4) that "bodies cannot be understood by the intellect; nor indeed anything corporeal unless it can be perceived by the senses." He says also (Gen. ad lit. xii, 24) that intellectual vision is of those things that are in the soul by their essence. But such are not bodies. Therefore the soul cannot know bodies through the intellect.
Objection 2: Further, as sense is to the intelligible, so is the intellect to the sensible. But the soul can by no means, through the senses, understand spiritual things, which are intelligible. Therefore by no means can it, through the intellect, know bodies, which are sensible.
Objection 3: Further, the intellect is concerned with things that are necessary and unchangeable. But all bodies are mobile and changeable. Therefore the soul cannot know bodies through the intellect.
On the contrary, Science is in the intellect. If, therefore, the intellect does not know bodies, it follows that there is no science of bodies; and thus perishes natural science, which treats of mobile bodies.
I answer that, It should be said in order to elucidate this question, that the early philosophers, who inquired into the natures of things, thought there was nothing in the world save bodies. And because they observed that all bodies are mobile, and considered them to be ever in a state of flux, they were of opinion that we can have no certain knowledge of the true nature of things. For what is in a continual state of flux, cannot be grasped with any degree of certitude, for it passes away ere the mind can form a judgment thereon: according to the saying of Heraclitus, that "it is not possible twice to touch a drop of water in a passing torrent," as the Philosopher relates (Metaph. iv, Did. iii, 5).
After these came Plato, who, wishing to save the certitude of our knowledge of truth through the intellect, maintained that, besides these things corporeal, there is another genus of beings, separate from matter and movement, which beings he called "species" or "ideas," by participation of which each one of these singular and sensible things is said to be either a man, or a horse, or the like. Wherefore he said that sciences and definitions, and whatever appertains to the act of the intellect, are not referred to these sensible bodies, but to those beings immaterial and separate: so that according to this the soul does not understand these corporeal things, but the separate species thereof.
Now this may be shown to be false for two reasons. First, because, since those species are immaterial and immovable, knowledge of movement and matter would be excluded from science (which knowledge is proper to natural science), and likewise all demonstration through moving and material causes. Secondly, because it seems ridiculous, when we seek for knowledge of things which are to us manifest, to introduce other beings, which cannot be the substance of those others, since they differ from them essentially: so that granted that we have a knowledge of those separate substances, we cannot for that reason claim to form a judgment concerning these sensible things.
Now it seems that Plato strayed from the truth because, having observed that all knowledge takes place through some kind of similitude, he thought that the form of the thing known must of necessity be in the knower in the same manner as in the thing known. Then he observed that the form of the thing understood is in the intellect under conditions of universality, immateriality, and immobility: which is apparent from the very operation of the intellect, whose act of understanding has a universal extension, and is subject to a certain amount of necessity: for the mode of action corresponds to the mode of the agent's form. Wherefore he concluded that the things which we understand must have in themselves an existence under the same conditions of immateriality and immobility.
But there is no necessity for this. For even in sensible things it is to be observed that the form is otherwise in one sensible than in another: for instance, whiteness may be of great intensity in one, and of a less intensity in another: in one we find whiteness with sweetness, in another without sweetness. In the same way the sensible form is conditioned differently in the thing which is external to the soul, and in the senses which receive the forms of sensible things without receiving matter, such as the color of gold without receiving gold. So also the intellect, according to its own mode, receives under conditions of immateriality and immobility, the species of material and mobile bodies: for the received is in the receiver according to the mode of the receiver. We must conclude, therefore, that through the intellect the soul knows bodies by a knowledge which is immaterial, universal, and necessary.
Reply to Objection 1: These words of Augustine are to be understood as referring to the medium of intellectual knowledge, and not to its object. For the intellect knows bodies by understanding them, not indeed through bodies, nor through material and corporeal species; but through immaterial and intelligible species, which can be in the soul by their own essence.