Summa Th. II-II EN Qu.89 a.6
Objection: 1. It would seem that it is not lawful to swear by creatures. It is written (Mt 5,34-36): "I say to you not to swear at all, neither by heaven . . . nor by the earth . . . nor by Jerusalem . . . nor by thy head": and Jerome, expounding these words, says: "Observe that the Saviour does not forbid swearing by God, but by heaven and earth," etc.
2. Further, punishment is not due save for a fault. Now a punishment is appointed for one who swears by creatures: for it is written (22, qu. i, can. Clericum): "If a cleric swears by creatures he must be very severely rebuked: and if he shall persist in this vicious habit we wish that he be excommunicated." Therefore it is unlawful to swear by creatures.
3. Further, an oath is an act of religion, as stated above (Article ). But religious worship is not due to any creature, according to Rm 1,23 Rm 1,25. Therefore it is not lawful to swear by a creature.
On the contrary Joseph swore "by the health of Pharaoh" (Gn 42,16). Moreover it is customary to swear by the Gospel, by relics, and by the saints.
I answer that As stated above (Article , ad 3), there are two kinds of oath. One is uttered a simple contestation or calling God as witness: and this kind of oath, like faith, is based on God's truth. Now faith is essentially and chiefly about God Who is the very truth, and secondarily about creatures in which God's truth is reflected, as stated above (Question , Article ). In like manner an oath is chiefly referred to God Whose testimony is invoked; and secondarily an appeal by oath is made to certain creatures considered, not in themselves, but as reflecting the Divine truth. Thus we swear by the Gospel, i.e. by God Whose truth is made known in the Gospel; and by the saints who believed this truth and kept it.The other way of swearing is by cursing and in this kind of oath a creature is adduced that the judgment of God may be wrought therein. Thus a man is wont to swear by his head, or by his son, or by some other thing that he loves, even as the Apostle swore (2Co 1,23), saying: "I call God to witness upon my soul."As to Joseph's oath by the health of Pharaoh this may be understood in both ways: either by way of a curse, as though he pledged Pharao's health to God; or by way of contestation, as though he appealed to the truth of God's justice which the princes of the earth are appointed to execute.
Reply to Objection: 1. Our Lord forbade us to swear by creatures so as to give them the reverence due to God. Hence Jerome adds that "the Jews, through swearing by the angels and the like, worshipped creatures with a Divine honor."In the same sense a cleric is punished, according to the canons (22, qu. i, can. Clericum, Objection ), for swearing by a creature, for this savors of the blasphemy of unbelief. Hence in the next chapter, it is said: "If any one swears by God's hair or head, or otherwise utter blasphemy against God, and he be in ecclesiastical orders, let him be degraded."
2. This suffices for the Reply to the Second Objection.
3. Religious worship is shown to one whose testimony is invoked by oath: hence the prohibition (Ex 23,13): "By the name of strange gods you shall not swear." But religious worship is not given to creatures employed in an oath in the ways mentioned above.
Objection: 1. It would seem that an oath has no binding force. An oath is employed in order to confirm the truth of an assertion. But when a person makes an assertion about the future his assertion is true, though it may not be verified. Thus Paul lied not (2Co 1,15, seqq.) though he went not to Corinth, as he had said he would (1Co 16,5). Therefore it seems that an oath is not binding.
2. Further, virtue is not contrary to virtue (Categ. viii, 22). Now an oath is an act of virtue, as stated above (Article ). But it would sometimes be contrary to virtue, or an obstacle thereto, if one were to fulfil what one has sworn to do: for instance, if one were to swear to commit a sin, or to desist from some virtuous action. Therefore an oath is not always binding.
3. Further, sometimes a man is compelled against his will to promise something under oath. Now, "such a person is loosed by the Roman Pontiffs from the bond of his oath" (Extra, De Jurejur., cap. Verum in ea quaest., etc.). Therefore an oath is not always binding.
4. Further, no person can be under two opposite obligations. Yet sometimes the person who swears and the person to whom he swears have opposite intentions. Therefore an oath cannot always be binding.
On the contrary It is written (Mt 5,33): "Thou shalt perform thy oaths to the Lord."
I answer that An obligation implies something to be done or omitted; so that apparently it regards neither the declaratory oath (which is about something present or past), nor such oaths as are about something to be effected by some other cause (as, for example, if one were to swear that it would rain tomorrow), but only such as are about things to be done by the person who swears.Now just as a declaratory oath, which is about the future or the present, should contain the truth, so too ought the oath which is about something to be done by us in the future. Yet there is a difference: since, in the oath that is about the past or present, this obligation affects, not the thing that already has been or is, but the action of the swearer, in the point of his swearing to what is or was already true; whereas, on the contrary, in the oath that is made about something to be done by us, the obligation falls on the thing guaranteed by oath. For a man is bound to make true what he has sworn, else his oath lacks truth.Now if this thing be such as not to be in his power, his oath is lacking in judgment of discretion: unless perchance what was possible when he swore become impossible to him through some mishap. as when a man swore to pay a sum of money, which is subsequently taken from him by force or theft. For then he would seem to be excused from fulfilling his oath, although he is bound to do what he can, as, in fact, we have already stated with regard to the obligation of a vow (Question , Article , ad 2). If, on the other hand, it be something that he can do, but ought not to, either because it is essentially evil, or because it is a hindrance to a good, then his oath is lacking in justice: wherefore an oath must not be kept when it involves a sin or a hindrance to good. For in either case "its result is evil" [*Cf. Bede, Homil. xix, in Decoll. S. Joan. Bapt.]Accordingly we must conclude that whoever swears to do something is bound to do what he can for the fulfilment of truth; provided always that the other two accompanying conditions be present, namely, judgment and justice.
Reply to Objection: 1. It is not the same with a simple assertion, and with an oath wherein God is called to witness: because it suffices for the truth of an assertion, that a person say what he proposes to do, since it is already true in its cause, namely, the purpose of the doer. But an oath should not be employed, save in a matter about which one is firmly certain: and, consequently, if a man employ an oath, he is bound, as far as he can, to make true what he has sworn, through reverence of the Divine witness invoked, unless it leads to an evil result, as stated.
2. An oath may lead to an evil result in two ways. First, because from the very outset it has an evil result, either through being evil of its very nature (as, if a man were to swear to commit adultery), or through being a hindrance to a greater good, as if a man were to swear not to enter religion, or not to become a cleric, or that he would not accept a prelacy, supposing it would be expedient for him to accept, or in similar cases. For oaths of this kind are unlawful from the outset: yet with a difference: because if a man swear to commit a sin, he sinned in swearing, and sins in keeping his oath: whereas if a man swear not to perform a greater good, which he is not bound to do withal, he sins indeed in swearing (through placing an obstacle to the Holy Ghost, Who is the inspirer of good purposes), yet he does not sin in keeping his oath, though he does much better if he does not keep it.Secondly, an oath leads to an evil result through some new and unforeseen emergency. An instance is the oath of Herod, who swore to the damsel, who danced before him, that he would give her what she would ask of him. For this oath could be lawful from the outset, supposing it to have the requisite conditions, namely, that the damsel asked what it was right to grant. but the fulfilment of the oath was unlawful. Hence Ambrose says (De Officiis i, 50): "Sometimes it is wrong to fulfil a promise, and to keep an oath; as Herod, who granted the slaying of John, rather than refuse what he had promised."
3. There is a twofold obligation in the oath which a man takes under compulsion: one, whereby he is beholden to the person to whom he promises something; and this obligation is cancelled by the compulsion, because he that used force deserves that the promise made to him should not be kept. The other is an obligation whereby a man is beholden to God, in virtue of which he is bound to fulfil what he has promised in His name. This obligation is not removed in the tribunal of conscience, because that man ought rather to suffer temporal loss, than violate his oath. He can, however, seek in a court of justice to recover what he has paid, or denounce the matter to his superior even if he has sworn to the contrary, because such an oath would lead to evil results since it would be contrary to public justice. The Roman Pontiffs, in absolving men from oaths of this kind, did not pronounce such oaths to be unbinding, but relaxed the obligation for some just cause.
4. When the intention of the swearer is not the same as the intention of the person to whom he swears, if this be due to the swearer's guile, he must keep his oath in accordance with the sound understanding of the person to whom the oath is made. Hence Isidore says (De Summo Bono ii, 31): "However artful a man may be in wording his oath, God Who witnesses his conscience accepts his oath as understood by the person to whom it is made." And that this refers to the deceitful oath is clear from what follows: "He is doubly guilty who both takes God's name in vain, and tricks his neighbor by guile." If, however, the swearer uses no guile, he is bound in accordance with his own intention. Wherefore Gregory says (Moral. xxvi, 7): "The human ear takes such like words in their natural outward sense, but the Divine judgment interprets them according to our inward intention."
Objection: 1. It would seem that an oath is more binding than a vow. A vow is a simple promise: whereas an oath includes, besides a promise, an appeal to God as witness. Therefore an oath is more binding than a vow.
2. Further, the weaker is wont to be confirmed by the stronger. Now a vow is sometimes confirmed by an oath. Therefore an oath is stronger than a vow.
3. Further, the obligation of a vow arises from the deliberation of the mind, a stated above (Question , Article ); while the obligation of an oath results from the truth of God Whose testimony is invoked. Since therefore God's truth is something greater than human deliberation, it seems that the obligation of an oath is greater than that of a vow.
On the contrary A vow binds one to God while an oath sometimes binds one to man. Now one is more bound to God than to man. Therefore a vow is more binding than an oath.
I answer that The obligation both of vow and of an oath arises from something Divine; but in different ways. For the obligation of a vow arises from the fidelity we owe God, which binds us to fulfil our promises to Him. On the other hand, the obligation of an oath arises from the reverence we owe Him which binds us to make true what we promise in His name. Now every act of infidelity includes an irreverence, but not conversely, because the infidelity of a subject to his lord would seem to be the greatest irreverence. Hence a vow by its very nature is more binding than an oath.
Reply to Objection: 1. A vow is not any kind of promise, but a promise made to God; and to be unfaithful to God is most grievous.
2. An oath is added to a vow not because it is more stable, but because greater stability results from "two immutable things" [*He 6,18].
3. Deliberation of the mind gives a vow its stability, on the part of the person who takes the vow: but it has a greater cause of stability on the part of God, to Whom the vow is offered.
Objection: 1. It would seem that no one can dispense from an oath. Just as truth is required for a declaratory oath, which is about the past or the present, so too is it required for a promissory oath, which is about the future. Now no one can dispense a man from swearing to the truth about present or past things. Therefore neither can anyone dispense a man from making truth that which he has promised by oath to do in the future.
2. Further, a promissory oath is used for the benefit of the person to whom the promise is made. But, apparently, he cannot release the other from his oath, since it would be contrary to the reverence of God. Much less therefore can a dispensation from this oath be granted by anyone.
3. Further, any bishop can grant a dispensation from a vow, except certain vows reserved to the Pope alone, as stated above (Question , Article , ad 3). Therefore in like manner, if an oath admits of dispensation, any bishop can dispense from an oath. And yet seemingly this is to be against the law [*Caus. XV, qu. 6, can. Auctoritatem, seqq.: Cap. Si vero, de Jurejurando]. Therefore it would seem that an oath does not admit of dispensation.
On the contrary A vow is more binding than an oath, as stated above (Article ). But a vow admits of dispensation and therefore an oath does also.
I answer that As stated above (Question , Article ), the necessity of a dispensation both from the law and from a vow arises from the fact that something which is useful and morally good in itself and considered in general, may be morally evil and hurtful in respect of some particular emergency: and such a case comes under neither law nor vow. Now anything morally evil or hurtful is incompatible with the matter of an oath: for if it be morally evil it is opposed to justice, and if it be hurtful it is contrary to judgment. Therefore an oath likewise admits of dispensation.
Reply to Objection: 1. A dispensation from an oath does not imply a permission to do anything against the oath: for this is impossible, since the keeping of an oath comes under a Divine precept, which does not admit of dispensation: but it implies that what hitherto came under an oath no longer comes under it, as not being due matter for an oath, just as we have said with regard to vows (Question , Article , ad 2). Now the matter of a declaratory oath, which is about something past or present, has already acquired a certain necessity, and has become unchangeable, wherefore the dispensation will regard not the matter but the act itself of the oath: so that such a dispensation would be directly contrary to the Divine precept. On the other hand, the matter of a promissory oath is something future, which admits of change, so that, to wit, in certain emergencies, it may be unlawful or hurtful, and consequently undue matter for an oath. Therefore a promissory oath admits of dispensation, since such dispensation regards the matter of an oath, and is not contrary to the Divine precept about the keeping of oaths.
2. One man may promise something under oath to another in two ways. First, when he promises something for his benefit: for instance, if he promise to serve him, or to give him money: and from such a promise he can be released by the person to whom he made it: for he is understood to have already kept his promise to him when he acts towards him according to his will. Secondly, one man promises another something pertaining to God's honor or to the benefit of others: for instance, if a man promise another under oath that he will enter religion, or perform some act of kindness. In this case the person to whom the promise is made cannot release him that made the promise, because it was made principally not to him but to God: unless perchance it included some condition, for instance, "provided he give his consent" or some such like condition.
3. Sometimes that which is made the matter of a promissory oath is manifestly opposed to justice, either because it is a sin, as when a man swears to commit a murder, or because it is an obstacle to a greater good, as when a man swears not to enter a religion: and such an oath requires no dispensation. But in the former case a man is bound not to keep such an oath, while in the latter it is lawful for him to keep or not to keep the oath, as stated above (Article , ad 2). Sometimes what is promised on oath is doubtfully right or wrong, useful or harmful, either in itself or under the circumstance. In this case any bishop can dispense. Sometimes, however, that which is promised under oath is manifestly lawful and beneficial. An oath of this kind seemingly admits not of dispensation but of commutation, when there occurs something better to be done for the common good, in which case the matter would seem to belong chiefly to the power of the Pope, who has charge over the whole Church; and even of absolute relaxation, for this too belongs in general to the Pope in all matters regarding the administration of things ecclesiastical. Thus it is competent to any man to cancel an oath made by one of his subjects in matters that come under his authority: for instance, a father may annul his daughter's oath, and a husband his wife's (Nb 30,6, seqq.), as stated above with regard to vows (Question , Articles ,9).
Objection: 1. It would seem that an oath is not voided by a condition of person or time. An oath, according to the Apostle (He 6,16), is employed for the purpose of confirmation. Now it is competent to anyone to confirm his assertion, and at any time. Therefore it would seem that an oath is not voided by a condition of person or time.
2. Further, to swear by God is more than to swear by the Gospels: wherefore Chrysostom [*Hom. xliv in the Opus Imperfectum falsely ascribed to St. John Chrysostom] says: "If there is a reason for swearing, it seems a small thing to swear by God, but a great thing to swear by the Gospels. To those who think thus, it must be said: Nonsense! the Scriptures were made for God's sake, not God for the sake of the Scriptures." Now men of all conditions and at all times are wont to swear by God. Much more, therefore, is it lawful to swear by the Gospels.
3. Further, the same effect does not proceed from contrary causes, since contrary causes produce contrary effects. Now some are debarred from swearing on account of some personal defect; children, for instance, before the age of fourteen, and persons who have already committed perjury. Therefore it would seem that a person ought not to be debarred from swearing either on account of his dignity, as clerics, or on account of the solemnity of the time.
4. Further, in this world no living man is equal in dignity to an angel: for it is written (Mt 11,11) that "he that is the lesser in the kingdom of heaven is greater than he," namely than John the Baptist, while yet living. Now an angel is competent to swear, for it is written (Ap 10,6) that the angel "swore by Him that liveth for ever and ever." Therefore no man ought to be excused from swearing, on account of his dignity.
On the contrary It is stated (II, qu. v, can. Si quis presbyter): "Let a priest be examined 'by his sacred consecration,' instead of being put on his oath": and (22, qu. v, can. Nullus): "Let no one in ecclesiastical orders dare to swear on the Holy Gospels to a layman."
I answer that Two things are to be considered in an oath. One is on the part of God, whose testimony is invoked, and in this respect we should hold an oath in the greatest reverence. For this reason children before the age of puberty are debarred from taking oaths [*Caus. XXII, qu. 5, can. Parvuli], and are not called upon to swear, because they have not yet attained the perfect use of reason, so as to be able to take a oath with due reverence. Perjurers also are debarred from taking an oath, because it is presumed from their antecedents that they will not treat an oath with the reverence due to it. For this same reason, in order that oaths might be treated with due reverence the law says (22, qu. v, can. Honestum): "It is becoming that he who ventures to swear on holy things should do so fasting, with all propriety and fear of God."The other thing to be considered is on the part of the man, whose assertion is confirmed by oath. For a man's assertion needs no confirmation save because there is a doubt about it. Now it derogates from a person's dignity that one should doubt about the truth of what he says, wherefore "it becomes not persons of great dignity to swear." For this reason the law says (II, qu. v, can. Si quis presbyter) that "priests should not swear for trifling reasons." Nevertheless it is lawful for them to swear if there be need for it, or if great good may result therefrom. Especially is this the case in spiritual affairs, when moreover it is becoming that they should take oath on days of solemnity, since they ought then to devote themselves to spiritual matters. Nor should they on such occasions take oaths temporal matters, except perhaps in cases grave necessity.
Reply to Objection: 1. Some are unable to confirm their own assertions on account of their own defect: and some there are whose words should be so certain that they need no confirmation.
2. The greater the thing sworn by, the holier and the more binding is the oath, considered in itself, as Augustine states (Ad Public., Ep. xlvii): and accordingly is a graver matter to swear by God than the Gospels. Yet the contrary may be the case on account of the manner of swearing for instance, an oath by the Gospels might be taken with deliberation and solemnity, and an oath by God frivolously and without deliberation.
3. Nothing prevents the same thing from arising out of contrary causes, by way of superabundance and defect. It is in this way that some are debarred from swearing, through being of so great authority that it is unbecoming for them to swear; while others are of such little authority that their oaths have no standing.
4. The angel's oath is adduced not on account of any defect in the angel, as though one ought not to credit his mere word, but in order to show that the statement made issues from God's infallible disposition. Thus too God is sometimes spoken of by Scripture as swearing, in order to express the immutability of His word, as the Apostle declares (He 6,17).
We must now consider the taking of God's name by way of adjuration: under which head there are three points of inquiry:
(1) Whether it is lawful to adjure a man?
(2) Whether it is lawful to adjure the demons?
(3) Whether it is lawful to adjure irrational creatures?
Objection: 1. It would seem that it is not lawful to adjure a man. Origen says (Tract. xxxv super Matth.): "I deem that a man who wishes to live according to the Gospel should not adjure another man. For if, according to the Gospel mandate of Christ, it be unlawful to swear, it is evident that neither is it lawful to adjure: and consequently it is manifest that the high-priest unlawfully adjured Jesus by the living God."
2. Further, whoever adjures a man, compels him after a fashion. But it is unlawful to compel a man against his will. Therefore seemingly it is also unlawful to adjure a man.
3. Further, to adjure is to induce a person to swear. Now it belongs to man's superior to induce him to swear, for the superior imposes an oath on his subject. Therefore subjects cannot adjure their superiors.
On the contrary Even when we pray God we implore Him by certain holy things: and the Apostle too besought the faithful "by the mercy of God" (Rm 12,1): and this seems to be a kind of adjuration. Therefore it is lawful to adjure.
I answer that A man who utters a promissory oath, swearing by his reverence for the Divine name, which he invokes in confirmation of his promise, binds himself to do what he has undertaken, and so orders himself unchangeably to do a certain thing. Now just as a man can order himself to do a certain thing, so too can he order others, by beseeching his superiors, or by commanding his inferiors, as stated above (Question , Article ). Accordingly when either of these orderings is confirmed by something Divine it is an adjuration. Yet there is this difference between them, that man is master of his own actions but not of those of others; wherefore he can put himself under an obligation by invoking the Divine name, whereas he cannot put others under such an obligation unless they be his subjects, whom he can compel on the strength of the oath they have taken.Therefore, if a man by invoking the name of God, or any holy thing, intends by this adjuration to put one who is not his subject under an obligation to do a certain thing, in the same way as he would bind himself by oath, such an adjuration is unlawful, because he usurps over another a power which he has not. But superiors may bind their inferiors by this kind of adjuration, if there be need for it.If, however, he merely intend, through reverence of the Divine name or of some holy thing, to obtain something from the other man without putting him under any obligation, such an adjuration may be lawfully employed in respect of anyone.
Reply to Objection: 1. Origen is speaking of an adjuration whereby a man intends to put another under an obligation, in the same way as he would bind himself by oath: for thus did the high-priest presume to adjure our Lord Jesus Christ [*Mt 26,63].
2. This argument considers the adjuration which imposes an obligation.
3. To adjure is not to induce a man to swear, but to employ terms resembling an oath in order to provoke another to do a certain thing.Moreover, we adjure God in one way and man in another; because when we adjure a man we intend to alter his will by appealing to his reverence for a holy thing: and we cannot have such an intention in respect of God Whose will is immutable. If we obtain something from God through His eternal will, it is due, not to our merits, but to His goodness.
Objection: 1. It would seem unlawful to adjure the demons. Origen says (Tract. xxxv, super Matth.): "To adjure the demons is not accordance with the power given by our Saviour: for this is a Jewish practice." Now rather than imitate the rites of the Jews, we should use the power given by Christ. Therefore it is not lawful to adjure the demons.
2. Further, many make use of necromantic incantations when invoking the demons by something Divine: and this is an adjuration. Therefore, if it be lawful to adjure the demons, it is lawful to make use of necromantic incantations, which is evidently false. Therefore the antecedent is false also.
3. Further, whoever adjures a person, by that very fact associates himself with him. Now it is not lawful to have fellowship with the demons, according to 1Co 10,20, "I would not that you should be made partakers with devils." Therefore it is not lawful to adjure the demons.
On the contrary It is written (Mc 16,17): "In My name they shall cast out devils." Now to induce anyone to do a certain thing for the sake of God's name is to adjure. Therefore it is lawful to adjure the demons.
I answer that As stated in the preceding article, there are two ways of adjuring: one by way of prayer or inducement through reverence of some holy thing: the other by way of compulsion. In the first way it is not lawful to adjure the demons because such a way seems to savor of benevolence or friendship, which it is unlawful to bear towards the demons. As to the second kind of adjuration, which is by compulsion, we may lawfully use it for some purposes, and not for others. For during the course of this life the demons are our adversaries: and their actions are not subject to our disposal but to that of God and the holy angels, because, as Augustine says (De Trin. iii, 4), "the rebel spirit is ruled by the just spirit." Accordingly we may repulse the demons, as being our enemies, by adjuring them through the power of God's name, lest they do us harm of soul or body, in accord with the Divine power given by Christ, as recorded by Lc 10,19: "Behold, I have given you power to tread upon serpents and scorpions, and upon all the power of the enemy: and nothing shall hurt you."It is not, however, lawful to adjure them for the purpose of learning something from them, or of obtaining something through them, for this would amount to holding fellowship with them: except perhaps when certain holy men, by special instinct or Divine revelation, make use of the demons' actions in order to obtain certain results: thus we read of the Blessed James [*the Greater; cf. Apocrypha, N.T., Hist. Certam. Apost. vi, 19] that he caused Hermogenes to be brought to him, by the instrumentality of the demons.
Reply to Objection: 1. Origen is speaking of adjuration made, not authoritatively by way of compulsion, but rather by way of a friendly appeal.
2. Necromancers adjure and invoke the demons in order to obtain or learn something from them: and this is unlawful, as stated above. Wherefore Chrysostom, commenting on our Lord's words to the unclean spirit (Mc 1,25), "Speak no more, and go out of the man," says: "A salutary teaching is given us here, lest we believe the demons, however much they speak the truth."
3. This argument considers the adjuration whereby the demon's help is besought in doing or learning something: for this savors of fellowship with them. On the other hand, to repulse the demons by adjuring them, is to sever oneself from their fellowship.
Objection: 1. It would seem unlawful to adjure an irrational creature. An adjuration consists of spoken words. But it is useless to speak to one that understands not, such as an irrational creature. Therefore it is vain and unlawful to adjure an irrational creature.
2. Further, seemingly wherever adjuration is admissible, swearing is also admissible. But swearing is not consistent with an irrational creature. Therefore it would seem unlawful to employ adjuration towards one.
3. Further, there are two ways of adjuring, as explained above (Articles ,2). One is by way of appeal; and this cannot be employed towards irrational creatures, since they are not masters of their own actions. The other kind of adjuration is by way of compulsion: and, seemingly, neither is it lawful to use this towards them, because we have not the power to command irrational creatures, but only He of Whom it was said (Mt 8,27): "For the winds and the sea obey Him." Therefore in no way, apparently, is it lawful to adjure irrational creatures.
On the contrary Simon and Jude are related to have adjured dragons and to have commanded them to withdraw into the desert. [*From the apocryphal Historiae Certam. Apost. vi. 19.]
I answer that Irrational creatures are directed to their own actions by some other agent. Now the action of what is directed and moved is also the action of the director and mover: thus the movement of the arrow is an operation of the archer. Wherefore the operation of the irrational creature is ascribed not only to it, but also and chiefly to God, Who disposes the movements of all things. It is also ascribed to the devil, who, by God's permission, makes use of irrational creatures in order to inflict harm on man.Accordingly the adjuration of an irrational creature may be of two kinds. First, so that the adjuration is referred to the irrational creature in itself: and in this way it would be vain to adjure an irrational creature. Secondly, so that it be referred to the director and mover of the irrational creature, and in this sense a creature of this kind may be adjured in two ways. First, by way of appeal made to God, and this relates to those who work miracles by calling on God: secondly, by way of compulsion, which relates to the devil, who uses the irrational creature for our harm. This is the kind of adjuration used in the exorcisms of the Church, whereby the power of the demons is expelled from an irrational creature. But it is not lawful to adjure the demons by beseeching them to help us.
Reply to Objection: 1. This suffices for the Replies to the Objections.
Summa Th. II-II EN Qu.89 a.6