Here I analyze St. Thomas Aquinas's Summa Theologica article that, contrary to most moderns who are steeped in a Cartesian idealism—viz., who think everything is in our heads—intellectual knowledge does indeed come from the senses. Overcoming modern Manicheans' and Albigenses' denial of this—i.e., that they think a human being is not both a body and an intellectual soul but just a soul trapped in a body, hence rationalizing any misuse of the human body, e.g., pornography, slavery, contraception, abortion, because the apparently evil body has no affect on oneself nor on one's soul—is vitally important both for society and for the proper development of modern physics, as the Institute of Advanced Physics recognizes and promotes. Nothing is in the intellect that is not first in the senses: Nihil est in intellectu quod non prius in sensu. (Refer to this post for an overview of this "Epistemology of Modern Physics" series.)
See future posts for the continuation of the commentary.
Article 6. Whether intellectual knowledge is derived from sensible things?
Objection 1. It would seem that intellectual knowledge is not derived from sensible things. For Augustine says (QQ. 83, qu. 9) that "we cannot expect to learn the fulness of truth from the senses of the body." This he proves in two ways. First, because "whatever the bodily senses reach, is continually being changed; and what is never the same cannot be perceived." Secondly, because, "whatever we perceive by the body, even when not present to the senses, may be present to the imagination, as when we are asleep or angry: yet we cannot discern by the senses, whether what we perceive be the sensible object or the deceptive image thereof. Now nothing can be perceived which cannot be distinguished from its counterfeit." And so he concludes that we cannot expect to learn the truth from the senses. But intellectual knowledge apprehends the truth. Therefore intellectual knowledge cannot be conveyed by the senses.[So would St. Augustine deny that anything can be sensed? Would he say that the senses always are a faulty and untrustworthy assessor of what is real?]
Objection 2. Further, Augustine says (Gen. ad lit. xii, 16): "We must not think that the body can make any impression on the spirit, as though the spirit were to supply the place of matter in regard to the body's action; for that which acts is in every way more excellent than that which it acts on." Whence he concludes that "the body does not cause its image in the spirit, but the spirit causes it in itself." Therefore intellectual knowledge is not derived from sensible things.[This seems to be a plausible argument. If the soul animates the body, then what effect can the body have on the soul? Is it a direct effect, or does the body change such that the soul animating it must correspondingly adapt to the change? Is this how it would communicate sense knowledge to the soul? Affecting how the soul can animate the body?]
Objection 3. Further, an effect does not surpass the power of its cause. But intellectual knowledge extends beyond sensible things: for we understand some things which cannot be perceived by the senses. Therefore intellectual knowledge is not derived from sensible things.[I suppose this is related to the fact that senses deal with particulars—"this atom," "that dog", etc.—than with universals—"atom-ness," "dog-ness," etc.—generalized from particulars. The human intellectual soul can only do this.]
I answer that, On this point the philosophers held three opinions. For Democritus held that "all knowledge is caused by images issuing from the bodies we think of and entering into our souls," as Augustine says in his letter to Dioscorus (cxviii, 4). And Aristotle says (De Somn. et Vigil.) that Democritus held that knowledge is cause by a "discharge of images." And the reason for this opinion was that both Democritus and the other early philosophers did not distinguish between intellect and sense, as Aristotle relates (De Anima iii, 3). Consequently, since the sense is affected by the sensible, they thought that all our knowledge is affected by this mere impression brought about by sensible things. Which impression Democritus held to be caused by a discharge of images.[So, in a way, Democritus thought that we had a sort of angelic, direct knowledge of objects via a "discharge of images" coming from them; thus, we knowledge not mediated by the senses. But this is just pushing the question into the realm of the unknown: What exactly are these images that are discharged? How are they distinguished? Does every soul interpret them similarly? How would you know? This seems to be a subtle form of Cartesian idealism.]
Plato, on the other hand, held that the intellect is distinct from the senses: and that it is an immaterial power not making use of a corporeal organ for its action.[Yes, not even the brain] And since the incorporeal cannot be affected by the corporeal, he held that intellectual knowledge is not brought about by sensible things affecting the intellect, but by separate intelligible forms being participated by the intellect, as we have said above (4,5) [and it would seem in the previous paragraph, too]. Moreover he held that sense is a power operating of itself. Consequently neither is sense, since it is a spiritual power, affected by the sensible: but the sensible organs are affected by the sensible, the result being that the soul is in a way roused to form within itself the species of the sensible. [How exactly?] Augustine seems to touch on this opinion (Gen. ad lit. xii, 24) where he says that the "body feels not, but the soul through the body, which it makes use of as a kind of messenger, for reproducing within itself what is announced from without." [This might be akin to what we said in the first comment above.] Thus according to Plato, neither does intellectual knowledge proceed from sensible knowledge, nor sensible knowledge exclusively from sensible things; but these rouse the sensible soul to the sentient act, while the senses rouse the intellect to the act of understanding.
Aristotle chose a middle course. For with Plato he agreed that intellect and sense are different. But he held that the sense has not its proper operation without the cooperation of the body [Now this is more reasonable because how can the senses not be corporeal?]; so that to feel is not an act of the soul alone, but of the "composite." [Yes, the body and soul, when a human is alive, are inextricably connected.] And he held the same in regard to all the operations of the sensitive part. Since, therefore, it is not unreasonable that the sensible objects which are outside the soul should produce some effect in the "composite," Aristotle agreed with Democritus in this, that the operations of the sensitive part are caused by the impression of the sensible on the sense: not by a discharge, as Democritus said, but by some kind of operation. [Through the physical] For Democritus maintained that every operation is by way of a discharge of atoms [not in the modern sense of "atom," though], as we gather from De Gener. i, 8. But Aristotle held that the intellect has an operation which is independent of the body's cooperation. Now nothing corporeal can make an impression on the incorporeal. [Agreed] And therefore in order to cause the intellectual operation according to Aristotle, the impression caused by the sensible does not suffice, but something more noble is required, for "the agent is more noble than the patient," as he says (De Gener. i, 5). Not, indeed, in the sense that the intellectual operation is effected in us by the mere impression of some superior beings, as Plato held; but that the higher and more noble agent which he calls the active intellect, of which we have spoken above (79, 3,4) [See Sentencia De anima, lib. 3 l. 10.] causes the phantasms received from the senses to be actually intelligible, by a process of abstraction.
According to this opinion, then, on the part of the phantasms, intellectual knowledge is caused by the senses. But since the phantasms cannot of themselves affect the passive intellect, and require to be made actually intelligible by the active intellect, it cannot be said that sensible knowledge is the total and perfect cause of intellectual knowledge, but rather that it is in a way the material cause.[Wow, so sense knowledge is like a material cause of intellectual knowledge. What would the formal cause be like, then? The phantasms? The light of reason? The active intellect? The fact that the passive and active intellect is one of the hardest things to understand definitely sheds light on the mystery of the relation between the senses and the soul, but it cannot disprove that sense knowledge is not like the form of intellectual knowledge.]
Reply to Objection 1. Those words of Augustine mean that we must not expect the entire truth from the senses. For the light of the active intellect is needed, through which we achieve the unchangeable truth of changeable things, and discern things themselves from their likeness.["[T]he light of the active intellect is needed." What about the principles afforded by Revelation, the truths of faith?]
Reply to Objection 2. In this passage Augustine speaks not of intellectual but of imaginary knowledge. And since, according to the opinion of Plato, the imagination has an operation which belongs to the soul only, Augustine, in order to show that corporeal images are impressed on the imagination, not by bodies but by the soul, uses the same argument as Aristotle does in proving that the active intellect must be separate, namely, because "the agent is more noble than the patient." And without doubt, according to the above opinion, in the imagination there must needs be not only a passive but also an active power. But if we hold, according to the opinion of Aristotle, that the action of the imagination, is an action of the "composite," there is no difficulty; because the sensible body is more noble than the organ of the animal, in so far as it is compared to it as a being in act to a being in potentiality; even as the object actually colored is compared to the pupil which is potentially colored. It may, however, be said, although the first impression of the imagination is through the agency of the sensible, since "fancy is movement produced in accordance with sensation" (De Anima iii, 3), that nevertheless there is in man an operation which by synthesis and analysis forms images of various things, even of things not perceived by the senses. And Augustine's words may be taken in this sense.
Reply to Objection 3. Sensitive knowledge is not the entire cause of intellectual knowledge. And therefore it is not strange that intellectual knowledge should extend further than sensitive knowledge.[What is the rest of the cause? "[T]he light of the active intellect?"]
—St. Thomas Aquinas's Summa Theologica Iª q. 84 a. 6 with my commentary in [red]