Article 6 — Whether the human mind receives knowledge from sensible things

Sixth it is asked whether the human mind receives knowledge from sensible things? (Parallel texts: below: q. 19, a. 1; ST I.84.6; Quodlibet, bk. 8, q. 2, a. 1; Compendium theologiae, cc. 81–83; Disputed Questions on the Soul, a. 15.)

Obj. 1: It seems that it does not, for action and passion cannot take place between things unless both are material, as is clear from Boethius, (Boethius, On the Person and the Two Natures: A Treatise Against Eutyches and Nestorius, ch. 6 (PL 64:1349D).) and also from the Philosopher. (Aristotle, On Generation 1.7, 324a34.) But our mind does not share in matter with sensible things. Therefore, sensible things cannot act on our mind to imprint knowledge on it.

Obj. 2: What a thing is, is the object of intellect, as is said in On the Soul. (Aristotle, On the Soul 3.6, 430b28.) But the quiddity of a thing is not perceived by any sense. Therefore, mental cognition is not received from sense.

Obj. 3: When speaking of the way in which we acquire cognition of intelligible things, Augustine says: they were there that is, intelligible in our mind, before I learned them, but they were not in my memory. (Augustine, Confessions, bk. 10, ch. 10 (PL 32:786).) Therefore, it seems that intelligible species are not received in the mind from the senses.

Obj. 4: Augustine proves (Augustine, On the Trinity, bk. 10, ch. 1 (PL 42:971).) that the soul can love only what it knows. But one loves a science before he learns it, as is clear from the eagerness with which he seeks this knowledge. Therefore, before he learns such a science, he has some acquaintance with it. So, it seems that the mind does not receive knowledge from sensible things.

Obj. 5: Augustine says: (Augustine, On the Literal Interpretation of Genesis, bk. 12, ch. 16 (PL 34:467).) the body does not make the image of the body in the spirit. Rather, the spirit itself will a wonderful swiftness which is ineffably far from the slowness of the body makes in itself the image of the body. Therefore, it seems that the mind does not receive intelligible species from sensible things but constructs them in itself.

Obj. 6: Augustine says (Augustine, On the Trinity, bk. 12, ch. 2 (PL 42:999).) that our mind judges about bodily things through non-bodily and eternal principles. But principles received from the senses are not of this kind. Therefore, it seems that the human mind does not receive knowledge from sensible things.

Obj. 7: If the mind receives knowledge from sensible things, it must do so because the species received from sensible things set the potential intellect in motion. But such species cannot influence the potential intellect. For, when they are in the imagination, they are not intelligible actually, but only potentially, and so cannot set the potential intellect in motion. The intellect, however, is moved only by something actually intelligible, just as the power of sight is moved only by something actually visible. Similarly, something existing in the agent intellect cannot move the potential intellect, because the agent intellect does not receive species. If it did, it would not differ from the potential intellect. Again, these representations do not actuate the potential intellect by existing in it, for a form already adhering in a subject does not set the subject in motion, but is, as it were, at rest in it. Finally, they do not cause movement in the potential intellect by existing of themselves, for intelligible species are not substances, but belong to the class of accidents, as Avicenna says. (Avicenna, Metaphysics, bk. 3, ch. 8.) Therefore, in no way can our mind receive knowledge from sensible things.

Obj. 8: The agent is more noble than the patient, as is clear from Augustine (Augustine, On the Literal Interpretation of Genesis, bk. 12, cc. 6, 16 (PL 34:467).) and from the Philosopher. (Aristotle, On the Soul 3.5, 430a18.) But the receiver is related to that which it receives, as a patient is related to the agent. Since, therefore, the mind is much more noble than sensible things and the senses themselves, it cannot receive knowledge from them.

Obj. 9: The Philosopher says (Aristotle, Physics 7.3, 247b23.) that the soul comes to acquire knowledge and prudence by coming to rest. But the soul cannot receive knowledge from sensible things unless it be somehow set in motion by them. Therefore, the soul does not receive knowledge from sensible things.

On the contrary (1), as the Philosopher says, (Aristotle, Posterior Analytics 1.18, 81a38; cf. ST I.78.4, obj. 4.) and as experience proves, one who lacks a sense is deprived of one kind of knowledge, as the blind have no knowledge of colors. This would not happen if the soul received knowledge from a source other than the senses. Therefore, the soul receives knowledge from sensible objects through the senses.

Furthermore (2), at first, all our cognition consists in the knowledge of first undeducible principles. But the cognition of these arises in us from sense, as is clear from the Posterior Analytics. (Aristotle, Posterior Analytics 2.19, 100a10.) Therefore, all our knowledge arises from sense.

Furthermore (3), nature does nothing to no purpose and does not fail in necessary matters. (Aristotle, On the Soul 3.9, 432b21.) But senses would have been given to the soul to no purpose unless the soul received cognition from things through them. Therefore, our mind receives knowledge from sensible things.

I answer that the views of the ancients on this question are manifold. Some held that our knowledge derived completely from an external cause separated from matter. There are two explanations of this position. Some, as the Platonists, held that the forms of sensible thing existed apart from matter and so were actually intelligible. According to them, real individuals come about through the participation by sensible matter in these forms, and the human mind has knowledge by sharing in them. Thus, these forms are the principle of generation and knowledge, as the Philosopher says. (Aristotle, Metaphysics 1.9, 991a8.) But the Philosopher has adequately confuted this position (Aristotle, Metaphysics 7.10, 1034b32–1035b3.) by showing that sensible forms must exist in sensible matter, and that sensible matter in general is necessary for the understanding of physical forms, just as there is no snub without nose. (Cf. Aristotle, Metaphysics 7.11, 1037a31.)

For this reason, others, bypassing separated forms of sensible things, demanded only intelligences, which we call angels, and made separated substances of this sort the sole source of our knowledge. Accordingly, Avicenna holds (Avicenna, On the Soul, bk. 5, ch. 5, as Thomas refers below, q. 11, a. 1; Metaphysics, bk. 9, cc. 2, 4–5.) that just as sensible forms are not received into sensible matter except through the influence of the agent intelligence, so, too, intelligible forms are not imprinted on human minds except by the agent intelligence, which for him (Avicenna, On the Soul, bk. 5, ch. 5.) is not a part of the soul, but a separated substance. However, the soul needs the senses to prepare the way and stimulate it to knowledge, just as the lower agents prepare matter to receive form from the agent intelligence. (Avicenna, Metaphysics, bk. 9, ch. 2.) But this opinion does not seem reasonable, because, according to it, there is no necessary interdependence of the human mind and the sensitive powers. The opposite seems quite clear both from the fact that, when a given sense is missing, we have no knowledge of its sensible objects, (Cf. Aristotle, Posterior Analytics 1.18, 81a38.) and from the fact that our mind cannot actually consider even those things which it knows habitually unless it forms some phantasms. Thus, an injury to the organ of imagination (Avicenna, On the Soul, bk. 4, ch. 1.) hinders consideration. Furthermore, the explanation just given does away with the proximate principles of things, inasmuch as all lower things would derive their intelligible and sensible forms immediately from a separated substance.

A second explanation has been given by those who make an inferior cause the complete source of our knowledge. There are also two explanations; of this position. Some (Platonists, as Thomas refers below, q. 18, a. 7, resp.; cf. Cicero, Tusculan Disputations, bk. 1, ch. 24, nn. 57–59; Augustine, On the Trinity, bk. 12, ch. 15 (PL 42:1011); On the Size of the Soul, ch. 20 (PL 32:1055); Macrobius, Commentary on the Dream of Scipio, bk. 1, ch. 12, nn. 6–10; Nemesius, On the Nature of Man, ch. 2 (PG 40:552); Boethius, Consolation of Philosophy, bk. 3, verse 11 (PL 63:777A).) held that human souls had within themselves knowledge of all things, but that this cognition was darkened by union with the body. Therefore, they said that we need assiduous use of the senses to remove the hindrance to knowledge. Learning, they said, is nothing but remembering, as is abundantly clear from the way in which those things which we have seen and heard make us remember what we formerly knew. But this position does not seem reasonable. For, if the union of soul and body is natural, it cannot wholly hinder natural knowledge. And if this opinion be true, we would not be subject to the complete ignorance of those objects which demand a sense faculty of which one is deprived. This opinion would fit in with the theory (Origen, On First Principles [Peri archon], bk. 2, ch. 9 (PG 11:230B–C), according to SCG II.83; cf. Augustine, City of God, ch. 23 (PL 41:336); Gennadius, On the Ecclesiastical Dogma, ch. 14 (PL 58:984B).) that holds that souls were created before bodies and later united to them. Then, the conjunction d body and soul would not be natural, but only an accidental accretion to the soul. This opinion must be rejected on the score both of faith (Cf. SCG II.83, at the end.) and philosophic tenets. (Cf. Bonaventure, In II Sent., d. 18, a. 2, q. 2.)

Other proponents (Adam Pulchre-Mulieris, De intelligentiis, prop. 30–32.) of this second opinion said that the soul is the cause of its own knowledge. For it does not receive knowledge from sensible things as if likenesses of things somehow reached the soul because of the activity of sensible things, but the soul itself, in the presence of sensible things, constructs in itself the likenesses of sensible things. But this statement does not seem altogether reasonable. For no agent acts except in so far as it is in act. (Cf. Aquinas, In II Sent., d. 1, q. 1, a. 2, s.c. 2; d. 17, q. 2, a. 1; SCG I.73; II.21; Aristotle, Physics 3.2, 202a11; Averroes, Physics, bk. 3, comm. 17; On the Soul, bk. 3, comm. 20.) Thus, if the soul formed the likenesses of all things in itself, it would be necessary for the soul to have those likenesses of things actually within itself. This would be a return to the previous opinion which held that the knowledge of all things is naturally present in the human soul.

Therefore, the opinion of the Philosopher (Aristotle, On the Soul 3.5, 430a10–25.) is more reasonable than any of the foregoing positions. He attributes the knowledge of our mind partly to intrinsic, partly to extrinsic, influence. Not only things separated from matter, but also sensible things themselves, play their part. For, when our mind is considered in relation to sensible things outside the soul, it is found to be related to them in a twofold manner. In one way, it is related as act to potency, to the extent that things outside the mind are only potentially intelligible. The mind itself, however, is intelligible in act, and it is on this basis that the agent intellect, which makes potentially intelligible things actually intelligible, is held to be included in the soul. In another way, it is related to things as potency to act, inasmuch as determined forms of things are only potentially in our mind, but actually in things outside the soul. In this respect our soul includes the potential intellect, whose function it is to receive forms abstracted from sensible things and made actually intelligible through the light of the agent intellect. This light of the agent intellect comes to the soul from the separated substances and especially from God as from its first source. (Cf. ST I.79.4.)

Accordingly, it is true that our mind receives knowledge from sensible things; nevertheless, the soul itself forms in itself likenesses of things, inasmuch as through the light of the agent intellect the forms abstracted from sensible things are made actually intelligible so that they may be received in the potential intellect. And in this way all knowledge is in a certain sense implanted in us from the beginning, since we have the light of the agent intellect, through the medium of universal conceptions which are immediately known by the light of the agent intellect. These serve as universal principles through which we judge about other things, and in which we foreknow these others. In this respect, that opinion is true which holds that we previously had in our knowledge those things which we learn.

Reply Obj. 1: Sensible forms, those, namely, which are abstracted from sensible things, cannot act on our mind unless they are rendered immaterial through the light of the agent intellect, and thus in some way are made homogeneous with the potential intellect on which they must act.

Reply Obj. 2: A higher and lower power do not operate in the same way even in respect to the same thing, but the higher power acts more nobly. Thus, when sense knows a thing through a form received from things, it does not know it so effectively as the intellect. Sense is led through it to a knowledge of the external accidents; the intellect reaches to the bare quiddity of the thing, distinguishing it from all material dispositions. Thus, when the mental knowing is said to take its origin from sense, this does not mean that sense apprehends all that the mind knows, but that, from those things which sense apprehends, the mind is led on to something more, just as the intellectual knowledge of sensible things leads to knowledge of divine things.

Reply Obj. 3: The statement from Augustine refers to that precognition by which we know particulars in universal principles. In this sense it is true that what we learn is already in our soul.

Reply Obj. 4: One can love scientific knowledge before he acquires it in so far as he has some general acquaintance with it by sight, or by knowing its usefulness, or in some other way.

Reply Obj. 5: The soul is to be understood to fashion itself in this sense, that the forms which arise from the activity of the agent intellect determine the potential intellect, as has been said. And in this sense, too, the imaginative power can fashion the forms of different sensible objects, as especially appears when we imagine things which we have never perceived by sense.

Reply Obj. 6: The first principles of which we have innate cognition are certain likenesses of uncreated truth. When we judge about other things through these likenesses, we are said to judge about things through unchangeable principles or through uncreated truth. Nevertheless, we should refer this statement of Augustine to higher reason, which confines itself to the contemplation of eternal truths. (Augustine, On the Trinity, bk. 12, ch. 7 (PL 42:1005).) Although this higher reason is first in dignity, its operation is subsequent in time: for the invisible things of him [God] . . . are clearly seen, being understood by the things that are made (Rom 1:20).

Reply Obj. 7: In the reception through which the potential intellect receives species from phantasms, the phantasms act as instrumental and secondary agents. The agent intellect acts as the principal and first agent. Therefore, the effect of the action is received in the potential intellect according to the condition of both, and not according to the condition of either one alone. Therefore, the potential intellect receives forms whose actual intelligibility is due to the power of the agent intellect, but whose determinate likeness to things is due to cognition of the phantasms. These actually intelligible forms do not, of themselves, exist either in the imagination or the agent intellect, but only in the potential intellect.

Reply Obj. 8: Although the potential intellect is simply more noble than the phantasm, nothing prevents the phantasm from being more noble n a certain respect, namely, that it is actually the likeness of such a thing, whereas this likeness belongs to the potential intellect only potentially. Thus, in a certain sense, we can say that the phantasm acts on the potential intellect in virtue of the light of the agent intellect, just as color can act on sight in virtue of bodily light.

Reply Obj. 9: The rest in which knowledge is achieved eliminates the movement of material passions. It does not eliminate movement and passion in a general sense, inasmuch as all receiving is called passion and movement. In accord with this, the Philosopher says in On the Soul: intellection is a kind of passion. (Aristotle, On the Soul 3.4, 429b24.)