Here is a brief overview of what these questions address:
Question 84. How the soul while united to the body understands corporeal things beneath it
- Does the soul know bodies through the intellect?
- Does it understand them through its essence, or through any species?
- If through some species, are the species of all things intelligible naturally innate in the soul?
- Are these species derived by the soul from certain separate immaterial forms?
- Does our soul see in the eternal ideas all that it understands?
- Does it acquire intellectual knowledge from the senses?
- Can the intellect, through the species of which it is possessed, actually understand, without turning to the phantasms?
- Is the judgment of the intellect hindered by an obstacle in the sensitive powers?
- Does our intellect understand by abstracting the species from the phantasms?
- Are the intelligible species abstracted from the phantasms what our intellect understands, or that whereby it understands?
- Does our intellect naturally first understand the more universal?
- Can our intellect know many things at the same time?
- Does our intellect understand by the process of composition and division?
- Can the intellect err?
- Can one intellect understand better than another?
- Does our intellect understand the indivisible before the divisible?
- Does it know singulars?
- Does it know the infinite?
- Does it know contingent things?
- Does it know future things?
- Can the soul separated from the body understand?
- Does it understand separate substances?
- Does it understand all natural things?
- Does it understand individuals and singulars?
- Do the habits of knowledge acquired in this life remain?
- Can the soul use the habit of knowledge here acquired?
- Does local distance impede the separated soul's knowledge?
- Do souls separated from the body know what happens here?
- "Soul," or anima in Latin, means "The principle of thought and action in man, commonly regarded as an entity distinct from the body; the spiritual part of man in contrast to the purely physical." (Oxford English Dictionary). The soul is the form of the human body and is roughly synonymous with "mind."
- "Phantasm" is a philosophical term for "A mental image, appearance, or representation, considered as the immediate object of sense perception (as distinct from the external thing itself or, in Platonic thought, its underlying form), or as the means by which the mind grasps the intelligible form of an object." (Oxford English Dictionary).
- "Motion" is "Any kind of change; becoming." (Oxford English Dictionary).
- "Angels" are "intellectual beings."
Beginning with the first article of Question 84, again with my commentary in [red]:
See future posts for the continuation of the commentary.
Article 1. Whether the soul knows bodies through the intellect?[How else would one know them? Through the means of physics experiments and instruments only?]
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.[Thus St. Augustine would agree that one cannot understand, e.g., the hydrogen atom without first performing experiments with instruments that make its effects perceptible to us; viz., we cannot understand corporeal objects with our intellects only, as Aristotle tried: Theoretical physics without experimentation is pure speculation.]
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.[Atheists, e.g., would deny that spiritual things are intelligible, though.]
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.[That "the intellect is concerted with things that are necessary and unchangeable" is another way of saying that the intellect strives for universal, certain knowledge. It tries to understand not just why, e.g., this particular measured hydrogen atom displays certain properties but what the universal nature of all hydrogen atoms must necessarily be.]
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.[No natural scientist can deny this claim. Also, by "mobile bodies" St. Thomas means changeable ones.]
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).[It is interesting that St. Thomas says that "that the early philosophers, who inquired into the natures of things, thought there was nothing in the world save bodies." Many modern scientists, from Descartes to Galileo to those in the present today, still believe in this claim. They believe in materialism, which says only matter and its movements exist, and in positivism, which holds that empirical science can justify every rational truth and therefore denies the supernatural or metaphysical, that which is "beyond physics." Galileo, being a mechanist, wrote extensively on how there is nothing more to the nature of, e.g., a feather than its mechanical movement, and this is all that is necessary for describing how we sense its tickling the skin.]
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.[This makes more sense because the objects physicists study through the mediation of experimentation are not the same as those one directly perceives in everyday experience. Who has ever touched or tasted, e.g., a quantum wavefuction? These things are indeed in the physical realm, not the directly sensible corporeal realm; they are a "separate species."]
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.[Notice he says modeling "things which are to us [already] manifest" is ridiculous. He is not saying that modeling the nature of subatomic particles, e.g., is ridiculous because their nature is not manifest, hence it is necessary that we model them since we cannot directly sense them.]
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.[According to Pope Benedict XVI, modern science is Platonic. Aristotle would say that the form exists in the matter, not separate from it. It is only our intellect that abstracts different formal objects from a certain material object.]
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.[When we understand gold, we do not have gold in our soul; rather, we have a particular formal object "in the receiver according to the mode of the receiver." This is not invented by the particular intellect, as the Kantians or Cartesians would say, nor is it equal to the material object as it would be in the intellect of an angel ("intellectual being"), which perceives things at once, not through reasoning, dividing, or composing as humans must do. For example, we consider charge separately from mass, then recompose the concepts to understand what a "charged mass" is. We start from axioms, such as in Euclidean geometry, and argue discursively to conclusions; but to angels these things are apparent at once.]
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.[Yes, sense-knowledge—even that obtained through empirical data and experiments—is the medium through which we ultimately gain knowledge, which ultimately resides in the soul.]
Reply to Objection 2. As Augustine says (De Civ. Dei xxii, 29), it is not correct to say that as the sense knows only bodies so the intellect knows only spiritual things; for it follows that God and the angels would not know corporeal things. The reason of this diversity is that the lower power does not extend to those things that belong to the higher power; whereas the higher power operates in a more excellent manner those things which belong to the lower power.
Reply to Objection 3. Every movement presupposes something immovable: for when a change of quality occurs, the substance remains unmoved; and when there is a change of substantial form, matter remains unmoved. Moreover the various conditions of mutable things are themselves immovable; for instance, though Socrates be not always sitting, yet it is an immovable truth that whenever he does sit he remains in one place. For this reason there is nothing to hinder our having an immovable science of movable things.
—St. Thomas Aquinas's Summa Theologica Iª q. 84 a. 1