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Summa Theologica, by St. Thomas Aquinas, [1947], at


We have next to consider those things which pertain to the action of man, who is composed of a created corporeal and spiritual nature. In the first place we shall consider that action (in general) and secondly in regard to the propagation of man from man. As to the first, there are four points of inquiry:

(1) Whether one man can teach another, as being the cause of his knowledge?

(2) Whether man can teach an angel?

(3) Whether by the power of his soul man can change corporeal matter?

(4) Whether the separate soul of man can move bodies by local movement?

Whether one man can teach another?

Objection 1: It would seem that one man cannot teach another. For the Lord says (Mat. 22:8): "Be not you called Rabbi": on which the gloss of Jerome says, "Lest you give to men the honor due to God." Therefore to be a master is properly an honor due to God. But it belongs to a master to teach. Therefore man cannot teach, and this is proper to God.

Objection 2: Further, if one man teaches another this is only inasmuch as he acts through his own knowledge, so as to cause knowledge in the other. But a quality through which anyone acts so as to produce his like, is an active quality. Therefore it follows that knowledge is an active quality just as heat is.

Objection 3: Further, for knowledge we require intellectual light, and the species of the thing understood. But a man cannot cause either of these in another man. Therefore a man cannot by teaching cause knowledge in another man.

Objection 4: Further, the teacher does nothing in regard to a disciple save to propose to him certain signs, so as to signify something by words or gestures. But it is not possible to teach anyone so as to cause knowledge in him, by putting signs before him. For these are signs either of things that he knows, or of things he does not know. If of things that he knows, he to whom these signs are proposed is already in the possession of knowledge, and does not acquire it from the master. If they are signs of things that he does not know, he can learn nothing therefrom: for instance, if one were to speak Greek to a man who only knows Latin, he would learn nothing thereby. Therefore in no way can a man cause knowledge in another by teaching him.

On the contrary, The Apostle says (1 Tim. 2:7): "Whereunto I am appointed a preacher and an apostle . . . a doctor of the Gentiles in faith and truth."

I answer that, On this question there have been various opinions. For Averroes, commenting on De Anima iii, maintains that all men have one passive intellect in common, as stated above (Q[76], A[2]). From this it follows that the same intelligible species belong to all men. Consequently he held that one man does not cause another to have a knowledge distinct from that which he has himself; but that he communicates the identical knowledge which he has himself, by moving him to order rightly the phantasms in his soul, so that they be rightly disposed for intelligible apprehension. This opinion is true so far as knowledge is the same in disciple and master, if we consider the identity of the thing known: for the same objective truth is known by both of them. But so far as he maintains that all men have but one passive intellect, and the same intelligible species, differing only as to various phantasms, his opinion is false, as stated above (Q[76], A[2]).

Besides this, there is the opinion of the Platonists, who held that our souls are possessed of knowledge from the very beginning, through the participation of separate forms, as stated above (Q[84], AA[3],4); but that the soul is hindered, through its union with the body, from the free consideration of those things which it knows. According to this, the disciple does not acquire fresh knowledge from his master, but is roused by him to consider what he knows; so that to learn would be nothing else than to remember. In the same way they held that natural agents only dispose (matter) to receive forms, which matter acquires by a participation of separate substances. But against this we have proved above (Q[79], A[2]; Q[84], A[3]) that the passive intellect of the human soul is in pure potentiality to intelligible (species), as Aristotle says (De Anima iii, 4).

We must therefore decide the question differently, by saying that the teacher causes knowledge in the learner, by reducing him from potentiality to act, as the Philosopher says (Phys. viii, 4). In order to make this clear, we must observe that of effects proceeding from an exterior principle, some proceed from the exterior principle alone; as the form of a house is caused to be in matter by art alone: whereas other effects proceed sometimes from an exterior principle, sometimes from an interior principle: thus health is caused in a sick man, sometimes by an exterior principle, namely by the medical art, sometimes by an interior principle as when a man is healed by the force of nature. In these latter effects two things must be noticed. First, that art in its work imitates nature for just as nature heals a man by alteration, digestion, rejection of the matter that caused the sickness, so does art. Secondly, we must remark that the exterior principle, art, acts, not as principal agent, but as helping the principal agent, but as helping the principal agent, which is the interior principle, by strengthening it, and by furnishing it with instruments and assistance, of which the interior principle makes use in producing the effect. Thus the physician strengthens nature, and employs food and medicine, of which nature makes use for the intended end.

Now knowledge is acquired in man, both from an interior principle, as is clear in one who procures knowledge by his own research; and from an exterior principle, as is clear in one who learns (by instruction). For in every man there is a certain principle of knowledge, namely the light of the active intellect, through which certain universal principles of all the sciences are naturally understood as soon as proposed to the intellect. Now when anyone applies these universal principles to certain particular things, the memory or experience of which he acquires through the senses; then by his own research advancing from the known to the unknown, he obtains knowledge of what he knew not before. Wherefore anyone who teaches, leads the disciple from things known by the latter, to the knowledge of things previously unknown to him; according to what the Philosopher says (Poster. i, 1): "All teaching and all learning proceed from previous knowledge."

Now the master leads the disciple from things known to knowledge of the unknown, in a twofold manner. Firstly, by proposing to him certain helps or means of instruction, which his intellect can use for the acquisition of science: for instance, he may put before him certain less universal propositions, of which nevertheless the disciple is able to judge from previous knowledge: or he may propose to him some sensible examples, either by way of likeness or of opposition, or something of the sort, from which the intellect of the learner is led to the knowledge of truth previously unknown. Secondly, by strengthening the intellect of the learner; not, indeed, by some active power as of a higher nature, as explained above (Q[106], A[1]; Q[111], A[1]) of the angelic enlightenment, because all human intellects are of one grade in the natural order; but inasmuch as he proposes to the disciple the order of principles to conclusions, by reason of his not having sufficient collating power to be able to draw the conclusions from the principles. Hence the Philosopher says (Poster. i, 2) that "a demonstration is a syllogism that causes knowledge." In this way a demonstrator causes his hearer to know.

Reply to Objection 1: As stated above, the teacher only brings exterior help as the physician who heals: but just as the interior nature is the principal cause of the healing, so the interior light of the intellect is the principal cause of knowledge. But both of these are from God. Therefore as of God is it written: "Who healeth all thy diseases" (Ps. 102:3); so of Him is it written: "He that teacheth man knowledge" (Ps. 93:10), inasmuch as "the light of His countenance is signed upon us" (Ps. 4:7), through which light all things are shown to us.

Reply to Objection 2: As Averroes argues, the teacher does not cause knowledge in the disciple after the manner of a natural active cause. Wherefore knowledge need not be an active quality: but is the principle by which one is directed in teaching, just as art is the principle by which one is directed in working.

Reply to Objection 3: The master does not cause the intellectual light in the disciple, nor does he cause the intelligible species directly: but he moves the disciple by teaching, so that the latter, by the power of his intellect, forms intelligible concepts, the signs of which are proposed to him from without.

Reply to Objection 4: The signs proposed by the master to the disciple are of things known in a general and confused manner; but not known in detail and distinctly. Therefore when anyone acquires knowledge by himself, he cannot be called self-taught, or be said to have his own master because perfect knowledge did not precede in him, such as is required in a master.

Whether man can teach the angels?

Objection 1: It would seem that men teach angels. For the Apostle says (Eph. 3:10): "That the manifold wisdom of God may be made known to the principalities and powers in the heavenly places through the Church." But the Church is the union of all the faithful. Therefore some things are made known to angels through men.

Objection 2: Further, the superior angels, who are enlightened immediately concerning Divine things by God, can instruct the inferior angels, as stated above (Q[116], A[1]; Q[112], A[3]). But some men are instructed immediately concerning Divine things by the Word of God; as appears principally of the apostles fromHeb. 1:1, 2: "Last of all, in these days (God) hath spoken to us by His Son." Therefore some men have been able to teach the angels.

Objection 3: Further, the inferior angels are instructed by the superior. But some men are higher than some angels; since some men are taken up to the highest angelic orders, as Gregory says in a homily (Hom. xxxiv in Evang.). Therefore some of the inferior angels can be instructed by men concerning Divine things.

On the contrary, Dionysius says (Div. Nom. iv) that every Divine enlightenment to the superior angels, by making their thoughts known to them; but concerning Divine things superior angels are never enlightened by inferior angels. Now it is manifest that in the same way as inferior angels are subject to the superior, the highest men are subject even to the lowest angels. This is clear from Our Lord's words (Mat. 11:11): "There hath not risen among them that are born of woman a greater than John the Baptist; yet he that is lesser in the kingdom of heaven is greater than he." Therefore angels are never enlightened by men concerning Divine things. But men can by means of speech make known to angels the thoughts of their hearts: because it belongs to God alone to know the heart's secrets.

Reply to Objection 1: Augustine (Gen. ad lit. v, 19) thus explains this passage of the Apostle, who in the preceding verses says: "To me, the least of all the saints, is given this grace . . . to enlighten all men, that they may see what is the dispensation of the mystery which hath been hidden from eternity in God. Hidden, yet so that the multiform wisdom of God was made known to the principalities and powers in the heavenly places---that is, through the Church." As though he were to say: This mystery was hidden from men, but not from the Church in heaven, which is contained in the principalities and powers who knew it "from all ages, but not before all ages: because the Church was at first there, where after the resurrection this Church composed of men will be gathered together."

It can also be explained otherwise that "what is hidden, is known by the angels, not only in God, but also here where when it takes place and is made public," as Augustine says further on (Gen. ad lit. v, 19). Thus when the mysteries of Christ and the Church were fulfilled by the apostles, some things concerning these mysteries became apparent to the angels, which were hidden from them before. In this way we can understand what Jerome says (Comment. in Ep. ad Eph.)---that from the preaching of the apostles the angels learned certain mysteries; that is to say, through the preaching of the apostles, the mysteries were realized in the things themselves: thus by the preaching of Paul the Gentiles were converted, of which mystery the Apostle is speaking in the passage quoted.

Reply to Objection 2: The apostles were instructed immediately by the Word of God, not according to His Divinity, but according as He spoke in His human nature. Hence the argument does not prove.

Reply to Objection 3: Certain men in this state of life are greater than certain angels, not actually, but virtually; forasmuch as they have such great charity that they can merit a higher degree of beatitude than that possessed by certain angels. In the same way we might say that the seed of a great tree is virtually greater than a small tree, though actually it is much smaller.

Whether man by the power of his soul can change corporeal matter?

Objection 1: It would seem that man by the power of his soul can change corporeal matter. For Gregory says (Dialog. ii, 30): "Saints work miracles sometimes by prayer, sometimes by their power: thus Peter, by prayer, raised the dead Tabitha to life, and by his reproof delivered to death the lying Ananias and Saphira." But in the working of miracles a change is wrought in corporeal matter. Therefore men, by the power of the soul, can change corporeal matter.

Objection 2: Further, on these words (Gal. 3:1): "Who hath bewitched you, that you should not obey the truth?" the gloss says that "some have blazing eyes, who by a single look bewitch others, especially children." But this would not be unless the power of the soul could change corporeal matter. Therefore man can change corporeal matter by the power of his soul.

Objection 3: Further, the human body is nobler than other inferior bodies. But by the apprehension of the human soul the human body is changed to heat and cold, as appears when a man is angry or afraid: indeed this change sometimes goes so far as to bring on sickness and death. Much more, then, can the human soul by its power change corporeal matter.

On the contrary, Augustine says (De Trin. iii, 8): "Corporeal matter obeys God alone at will."

I answer that, As stated above (Q[110], A[2]), corporeal matter is not changed to (the reception of) a form save either by some agent composed of matter and form, or by God Himself, in whom both matter and form pre-exist virtually, as in the primordial cause of both. Wherefore of the angels also we have stated (Q[110], A[2]) that they cannot change corporeal matter by their natural power, except by employing corporeal agents for the production of certain effects. Much less therefore can the soul, by its natural power, change corporeal matter, except by means of bodies.

Reply to Objection 1: The saints are said to work miracles by the power of grace, not of nature. This is clear from what Gregory says in the same place: "Those who are sons of God, in power, as John says---what wonder is there that they should work miracles by that power?"

Reply to Objection 2: Avicenna assigns the cause of bewitchment to the fact that corporeal matter has a natural tendency to obey spiritual substance rather than natural contrary agents. Therefore when the soul is of strong imagination, it can change corporeal matter. This he says is the cause of the "evil eye."

But it has been shown above (Q[110], A[2]) that corporeal matter does not obey spiritual substances at will, but the Creator alone. Therefore it is better to say, that by a strong imagination the (corporeal) spirits of the body united to that soul are changed, which change in the spirits takes place especially in the eyes, to which the more subtle spirits can reach. And the eyes infect the air which is in contact with them to a certain distance: in the same way as a new and clear mirror contracts a tarnish from the look of a "menstruata," as Aristotle says (De Somn. et Vigil.; [*De Insomniis ii]).

Hence then when a soul is vehemently moved to wickedness, as occurs mostly in little old women, according to the above explanation, the countenance becomes venomous and hurtful, especially to children, who have a tender and most impressionable body. It is also possible that by God's permission, or from some hidden deed, the spiteful demons co-operate in this, as the witches may have some compact with them.

Reply to Objection 3: The soul is united to the body as its form; and the sensitive appetite, which obeys the reason in a certain way, as stated above (Q[81], A[3]), it is the act of a corporeal organ. Therefore at the apprehension of the human soul, the sensitive appetite must needs be moved with an accompanying corporeal operation. But the apprehension of the human soul does not suffice to work a change in exterior bodies, except by means of a change in the body united to it, as stated above (ad 2).

Whether the separate human soul can move bodies at least locally?

Objection 1: It seems that the separate human soul can move bodies at least locally. For a body naturally obeys a spiritual substance as to local motion, as stated above (Q[110], A[5]). But the separate soul is a spiritual substance. Therefore it can move exterior bodies by its command.

Objection 2: Further, in the Itinerary of Clement it is said in the narrative of Nicetas to Peter, that Simon Magus, by sorcery retained power over the soul of a child that he had slain, and that through this soul he worked magical wonders. But this could not have been without some corporeal change at least as to place. Therefore, the separate soul has the power to move bodies locally.

On the contrary, the Philosopher says (De Anima i, 3) that the soul cannot move any other body whatsoever but its own.

I answer that, The separate soul cannot by its natural power move a body. For it is manifest that, even while the soul is united to the body, it does not move the body except as endowed with life: so that if one of the members become lifeless, it does not obey the soul as to local motion. Now it is also manifest that no body is quickened by the separate soul. Therefore within the limits of its natural power the separate soul cannot command the obedience of a body; though, by the power of God, it can exceed those limits.

Reply to Objection 1: There are certain spiritual substances whose powers are not determinate to certain bodies; such are the angels who are naturally unfettered by a body; consequently various bodies may obey them as to movement. But if the motive power of a separate substance is naturally determinate to move a certain body, that substance will not be able to move a body of higher degree, but only one of lower degree: thus according to philosophers the mover of the lower heaven cannot move the higher heaven. Wherefore, since the soul is by its nature determinate to move the body of which it is the form, it cannot by its natural power move any other body.

Reply to Objection 2: As Augustine (De Civ. Dei x, 11) and Chrysostom (Hom. xxviii in Matt.) say, the demons often pretend to be the souls of the dead, in order to confirm the error of heathen superstition. It is therefore credible that Simon Magus was deceived by some demon who pretended to be the soul of the child whom the magician had slain.