Summa Th. II-II EN Qu.87


Next we must consider tithes, under which head there are four points of inquiry:

(1) Whether men are bound by precept to pay tithes?

(2) Of what things ought tithes to be paid?

(3) To whom ought they to be paid?

(4) Who ought to pay tithes?

Whether men are bound to pay tithes under a necessity of precept?

Objection: 1. It would seem that men are not bound by precept to pay tithes. The commandment to pay tithes is contained in the Old Law (Lv 27,30), "All tithes of the land, whether of corn or of the fruits of trees, are the Lord's," and further on (Lv 27,32): "Of all the tithes of oxen and sheep and goats, that pass under the shepherd's rod, every tenth that cometh shall be sanctified to the Lord." This cannot be reckoned among the moral precepts, because natural reason does not dictate that one ought to give a tenth part, rather than a ninth or eleventh. Therefore it is either a judicial or a ceremonial precept. Now, as stated above (I-II 103,3; I-II 104,3), during the time of grace men are hound neither to the ceremonial nor to the judicial precepts of the Old Law. Therefore men are not bound now to pay tithes.
2. Further, during the time of grace men are bound only to those things which were commanded by Christ through the Apostles, according to Mt 28,20, "Teaching them to observe all things whatsoever I have commanded you"; and Paul says (Ac 20,27): "I have not spared to declare unto you all the counsel of God." Now neither in the teaching of Christ nor in that of the apostles is there any mention of the paying of tithes: for the saying of our Lord about tithes (Mt 23,23), "These things you ought to have done" seems to refer to the past time of legal observance: thus Hilary says (Super Matth. can. xxiv): "The tithing of herbs, which was useful in foreshadowing the future, was not to be omitted." Therefore during the time of grace men are not bound to pay tithes.
3. Further, during the time of grace, men are not more bound to the legal observances than before the Law. But before the Law tithes were given, by reason not of a precept but of a vow. For we read (Gn 28,20 Gn 28,22) that Jacob "made a vow" saying: "If God shall be with me, and shall keep me in the way by which I walk . . . of all the things that Thou shalt give to me, I will offer tithes to Thee." Neither, therefore, during the time of grace are men bound to pay tithes.
4. Further, in the Old Law men were bound to pay three kinds of tithe. For it is written (Nb 18,23-24): "The sons of Levi . . . shall . . . be content with the oblation of tithes, which I have separated for their uses and necessities." Again, there were other tithes of which we read (Dt 14,22-23): "Every year thou shalt set aside the tithes of all thy fruits, that the earth bringeth forth year by year; and thou shalt eat before the Lord thy God in the place which He shall choose." And there were yet other tithes, of which it is written (Dt 14,28): "The third year thou shalt separate another tithe of all things that grow to thee at that time, and shalt lay it up within thy gates. And the Levite that hath no other part nor possession with thee, and the stranger, and the fatherless, and the widow, that are within thy gates, shall . . . eat and be filled." Now during the time of grace men are not bound to pay the second and third tithes. Neither therefore are they bound to pay the first.
5. Further, a debt that is due without any time being fixed for its payment, must be paid at once under pain of sin. Accordingly if during the time of grace men are bound, under necessity of precept, to pay tithes in those countries where tithes are not paid, they would all be in a state of mortal sin, and so would also be the ministers of the Church for dissembling. But this seems unreasonable. Therefore during the time of grace men are not bound under necessity of precept to pay tithes.

On the contrary Augustine [*Append. Serm. cclxxcii], whose words are quoted 16, qu. i [*Can. Decimae], says: "It is a duty to pay tithes, and whoever refuses to pay them takes what belongs to another."
I answer that In the Old Law tithes were paid for the sustenance of the ministers of God. Hence it is written (Ml 3,10): "Bring all the tithes into My [Vulg.: 'the'] store-house that there may be meat in My house." Hence the precept about the paying of tithes was partly moral and instilled in the natural reason; and partly judicial, deriving its force from its divine institution. Because natural reason dictates that the people should administer the necessaries of life to those who minister the divine worship for the welfare of the whole people even as it is the people's duty to provide a livelihood for their rulers and soldiers and so forth. Hence the Apostle proves this from human custom, saying (1Co 9,7): "Who serveth as a soldier at any time at his own charge? Who planteth a vineyard and eateth not of the fruit thereof?" But the fixing of the proportion to be offered to the ministers of divine worship does not belong to the natural law, but was determined by divine institution, in accordance with the condition of that people to whom the law was being given. For they were divided into twelve tribes, and the twelfth tribe, namely that of Levi, was engaged exclusively in the divine ministry and had no possessions whence to derive a livelihood: and so it was becomingly ordained that the remaining eleven tribes should give one-tenth part of their revenues to the Levites [*Nb 18,21] that the latter might live respectably; and also because some, through negligence, would disregard this precept. Hence, so far as the tenth part was fixed, the precept was judicial, since all institutions established among this people for the special purpose of preserving equality among men, in accordance with this people's condition, are called "judicial precepts." Nevertheless by way of consequence these institutions foreshadowed something in the future, even as everything else connected with them, according to 1Co 12, "All these things happened to them in figure." In this respect they had something in common with the "ceremonial precepts," which were instituted chiefly that they might be signs of the future. Hence the precept about paying tithes foreshadowed something in the future. For ten is, in a way, the perfect number (being the first numerical limit, since the figures do not go beyond ten but begin over again from one), and therefore he that gave a tenth, which is the sign of perfection, reserving the nine other parts for himself, acknowledged by a sign that imperfection was his part, and that the perfection which was to come through Christ was to be hoped for from God. Yet this proves it to be, not a ceremonial but a judicial precept, as stated above.There is this difference between the ceremonial and judicial precepts of the Law, as we stated above (I-II 104,3), that it is unlawful to observe the ceremonial precepts at the time of the New Law, whereas there is no sin in keeping the judicial precepts during the time of grace although they are not binding. Indeed they are bound to be observed by some, if they be ordained by the authority of those who have power to make laws. Thus it was a judicial precept of the Old Law that he who stole a sheep should restore four sheep (Ex 22,1), and if any king were to order this to be done his subjects would be bound to obey. In like manner during the time of the New Law the authority of the Church has established the payment of tithe; thus showing a certain kindliness, lest the people of the New Law should give less to the ministers of the New Testament than did the people of the Old Law to the ministers of the Old Testament; for the people of the New Law are under greater obligations, according to Mt 5,20, "Unless your justice abound more than that of the Scribes and Pharisees, you shall not enter into the kingdom of heaven," and, moreover, the ministers of the New Testament are of greater dignity than the ministers of the Old Testament, as the Apostle shows (2Co 3,7-8).Accordingly it is evident that man's obligation to pay tithes arises partly from natural law, partly from the institution of the Church; who, nevertheless, in consideration of the requirements of time and persons might ordain the payment of some other proportion.

Reply to Objection: 1. This suffices for the Reply to the First Objection.
2. The precept about paying tithes, in so far as it was a moral precept, was given in the Gospel by our Lord when He said (Mt 10,10) [*The words as quoted are from Lc 10,7: Matthew has 'meat' instead of 'hire']: "The workman is worthy of his hire," and the Apostle says the same (1Co 9,4 seqq.). But the fixing of the particular proportion is left to the ordinance of the Church.
3. Before the time of the Old Law the ministry of the divine worship was not entrusted to any particular person; although it is stated that the first-born were priests, and that they received a double portion. For this very reason no particular portion was directed to be given to the ministers of the divine worship: but when they met with one, each man of his own accord gave him what he deemed right. Thus Abraham by a kind of prophetic instinct gave tithes to Melchisedech, the priest of the Most High God, according to Gn 14,20, and again Jacob made a vow to give tithes [*Gn 28,20], although he appears to have vowed to do so, not by paying them to ministers, but for the purpose of the divine worship, for instance for the fulfilling of sacrifices, hence he said significantly: "I will offer tithes to Thee."
4. The second kind of tithe, which was reserved for the offering of sacrifices, has no place in the New Law, since the legal victims had ceased. But the third kind of tithe which they had to eat with the poor, is increased in the New Law, for our Lord commanded us to give to the poor not merely the tenth part, but all our surplus, according to Lc 11,41: "That which remaineth, give alms." Moreover the tithes that are given to the ministers of the Church should be dispensed by them for the use of the poor.
5. The ministers of the Church ought to be more solicitous for the increase of spiritual goods in the people, than for the amassing of temporal goods: and hence the Apostle was unwilling to make use of the right given him by the Lord of receiving his livelihood from those to whom he preached the Gospel, lest he should occasion a hindrance to the Gospel of Christ [*1Co 9,12]. Nor did they sin who did not contribute to his upkeep, else the Apostle would not have omitted to reprove them. In like manner the ministers of the Church rightly refrain from demanding the Church's tithes, when they could not demand them without scandal, on account of their having fallen into desuetude, or for some other reason. Nevertheless those who do not give tithes in places where the Church does not demand them are not in a state of damnation, unless they be obstinate, and unwilling to pay even if tithes were demanded of them.

Whether men are bound to pay tithes of all things?

Objection: 1. It would seem that men are not bound to give tithes of all things. The paying of tithes seems to be an institution of the Old Law. Now the Old Law contains no precept about personal tithes, viz. those that are payable on property acquired by one's own act, for instance by commerce or soldiering. Therefore no man is bound to pay tithes on such things.
2. Further, it is not right to make oblations of that which is ill-gotten, as stated above (Question [86], Article [3]). Now oblations, being offered to God immediately, seem to be more closely connected with the divine worship than tithes which are offered to the ministers. Therefore neither should tithes be paid on ill-gotten goods.
3. Further, in the last chapter of Leviticus (Lv 30,32) the precept of paying tithes refers only to "corn, fruits of trees" and animals "that pass under the shepherd's rod." But man derives a revenue from other smaller things, such as the herbs that grow in his garden and so forth. Therefore neither on these things is a man bound to pay tithes.
4. Further, man cannot pay except what is in his power. Now a man does not always remain in possession of all his profit from land and stock, since sometimes he loses them by theft or robbery; sometimes they are transferred to another person by sale; sometimes they are due to some other person, thus taxes are due to princes, and wages due to workmen. Therefore one ought not to pay tithes on such like things.

On the contrary It is written (Gn 28,22): "Of all things that Thou shalt give to me, I will offer tithes to Thee."
I answer that In judging about a thing we should look to its principle. Now the principle of the payment of tithes is the debt whereby carnal things are due to those who sow spiritual things, according to the saying of the Apostle (1Co 9,11), "If we have sown unto you spiritual things, is it a great matter if we reap your carnal things?" [thus implying that on the contrary "it is no great matter if we reap your carnal things"] [*The phrase in the brackets is omitted in the Leonine edition]. For this debt is the principle on which is based the commandment of the Church about the payment of tithes. Now whatever man possesses comes under the designation of carnal things. Therefore tithes must be paid on whatever one possesses.

Reply to Objection: 1. In accordance with the condition of that people there was a special reason why the Old Law did not include a precept about personal tithes; because, to wit, all the other tribes had certain possessions wherewith they were able to provide a sufficient livelihood for the Levites who had no possessions, but were not forbidden to make a profit out of other lawful occupations as the other Jews did. On the other hand the people of the New Law are spread abroad throughout the world, and many of them have no possessions, but live by trade, and these would contribute nothing to the support of God's ministers if they did not pay tithes on their trade profits. Moreover the ministers of the New Law are more strictly forbidden to occupy themselves in money-making trades, according to 2Tm 2,4, "No man being a soldier to God, entangleth himself with secular business." Wherefore in the New Law men are bound to pay personal tithes, according to the custom of their country and the needs of the ministers: hence Augustine, whose words are quoted 16, qu. 1, cap. Decimae, says [*Append. Serm. cclxxvii]: "Tithes must be paid on the profits of soldiering, trade or craft."
2. Things are ill-gotten in two ways. First, because the getting itself was unjust: such, for instance, are things gotten by robbery, theft or usury: and these a man is bound to restore, and not to pay tithes on them. If, however, a field be bought with the profits of usury, the usurer is bound to pay tithes on the produce, because the latter is not gotten usuriously but given by God. On the other hand certain things are said to be ill-gotten, because they are gotten of a shameful cause, for instance of whoredom or stage-playing, and the like. Such things a man is not bound to restore, and consequently he is bound to pay tithes on them in the same way as other personal tithes. Nevertheless the Church must not accept the tithe so long as those persons remain in sin, lest she appear to have a share in their sins: but when they have done penance, tithes may be accepted from them on these things.
3. Things directed to an end must be judged according to their fittingness to the end. Now the payment of tithes is due not for its own sake, but for the sake of the ministers, to whose dignity it is unbecoming that they should demand minute things with careful exactitude, for this is reckoned sinful according to the Philosopher (Ethic. iv, 2). Hence the Old Law did not order the payment of tithes on such like minute things, but left it to the judgment of those who are willing to pay, because minute things are counted as nothing. Wherefore the Pharisees who claimed for themselves the perfect justice of the Law, paid tithes even on these minute things: nor are they reproved by our Lord on that account, but only because they despised greater, i.e. spiritual, precepts; and rather did He show them to be deserving of praise in this particular, when He said (Mt 23,23): "These things you ought to have done," i.e. during the time of the Law, according to Chrysostom's [*Hom. xliv in the Opus Imperfectum falsely ascribed to St. John Chrysostom] commentary. This also seems to denote fittingness rather than obligation. Therefore now too men are not bound to pay tithes on such minute things, except perhaps by reason of the custom of one's country.
4. A man is not bound to pay tithes on what he has lost by theft or robbery, before he recovers his property: unless he has incurred the loss through his own fault or neglect, because the Church ought not to be the loser on that account. If he sell wheat that has not been tithed, the Church can command the tithes due to her, both from the buyer who has a thing due to the Church, and from the seller, because so far as he is concerned he has defrauded the Church: yet if one pays, the other is not bound. Tithes are due on the fruits of the earth, in so far as these fruits are the gift of God. Wherefore tithes do not come under a tax, nor are they subject to workmen's wages. Hence it is not right to deduct one's taxes and the wages paid to workmen, before paying tithes: but tithes must be paid before anything else on one's entire produce.

Whether tithes should be paid to the clergy?

Objection: 1. It would seem that tithes should not be paid to the clergy. Tithes were paid to the Levites in the Old Testament, because they had no portion in the people's possessions, according to Nb 18,23-24. But in the New Testament the clergy have possessions not only ecclesiastical, but sometimes also patrimonial: moreover they receive first-fruits, and oblations for the living and the dead. Therefore it is unnecessary to pay tithes to them.
2. Further, it sometimes happens that a man dwells in one parish, and farms in another; or a shepherd may take his flock within the bounds of one parish during one part of the year, and within the bounds of one parish during one part of the year, and within the bounds of another parish during the other part of the year; or he may have his sheepfold in one parish, and graze the sheep in another. Now in all these and similar cases it seems impossible to decide to which clergy the tithes ought to be paid. Therefore it would seem that no fixed tithe ought to be paid to the clergy.
3. Further, it is the general custom in certain countries for the soldiers to hold the tithes from the Church in fee; and certain religious receive tithes. Therefore seemingly tithes are not due only to those of the clergy who have care of souls.

On the contrary It is written (Nb 18,21): "I have given to the sons of Levi all the tithes of Israel for a possession, for the ministry wherewith they serve Me in the Tabernacle." Now the clergy are the successors of the sons of Levi in the New Testament. Therefore tithes are due to the clergy alone.
I answer that Two things have to be considered with regard to tithes: namely, the right to receive tithes, and the things given in the name of tithes. The right to receive tithes is a spiritual thing, for it arises from the debt in virtue of which the ministers of the altar have a right to the expenses of their ministry, and temporal things are due to those who sow spiritual things. This debt concerns none but the clergy who have care of souls, and so they alone are competent to have this right.On the other hand the things given in the name of tithes are material, wherefore they may come to be used by anyone, and thus it is that they fall into the hands of the laity.

Reply to Objection: 1. In the Old Law, as stated above (Article [1], ad 4), special tithes were earmarked for the assistance of the poor. But in the New Law the tithes are given to the clergy, not only for their own support, but also that the clergy may use them in assisting the poor. Hence they are not unnecessary; indeed Church property, oblations and first-fruits as well as tithes are all necessary for this same purpose.
2. Personal tithes are due to the church in whose parish a man dwells, while predial tithes seem more reasonably to belong to the church within whose bounds the land is situated. The law, however, prescribes that in this matter a custom that has obtained for a long time must be observed [*Cap. Cum sint, and Cap. Ad apostolicae, de Decimis, etc.]. The shepherd who grazes his flock at different seasons in two parishes, should pay tithe proportionately to both churches. And since the fruit of the flock is derived from the pasture, the tithe of the flock is due to the church in whose lands the flock grazes, rather than to the church on whose land the fold is situated.
3. Just as the Church can hand over to a layman the things she receives under the title of tithe, so too can she allow him to receive tithes that are yet to be paid, the right of receiving being reserved to the ministers of the Church. The motive may be either the need of the Church, as when tithes are due to certain soldiers through being granted to them in fee by the Church, or it may be the succoring of the poor; thus certain tithes have been granted by way of alms to certain lay religious, or to those that have no care of souls. Some religious, however, are competent to receive tithes, because they have care of souls.

Whether the clergy also are bound to pay tithes?

Objection: 1. It would seem that clerics also are bound to pay tithes. By common law [*Cap. Cum homines, de Decimis, etc.] the parish church should receive the tithes on the lands which are in its territory. Now it happens sometimes that the clergy have certain lands of their own on the territory of some parish church, or that one church has ecclesiastical property on the territory of another. Therefore it would seem that the clergy are bound to pay predial tithes.
2. Further, some religious are clerics; and yet they are bound to pay tithes to churches on account of the lands which they cultivate even with their own hands [*Cap. Ex parte, and Cap. Nuper.]. Therefore it would seem that the clergy are not immune from the payment of tithes.
3. Further, in the eighteenth chapter of Numbers (Nb 26,28), it is prescribed not only that the Levites should receive tithes from the people, but also that they should themselves pay tithes to the high-priest. Therefore the clergy are bound to pay tithes to the Sovereign Pontiff, no less than the laity are bound to pay tithes to the clergy.
4. Further, tithes should serve not only for the support of the clergy, but also for the assistance of the poor. Therefore, if the clergy are exempt from paying tithes, so too are the poor. Yet the latter is not true. Therefore the former is false.

On the contrary A decretal of Pope Paschal [*Paschal II] says: "It is a new form of exaction when the clergy demand tithes from the clergy" [*Cap. Novum genus, de Decimis, etc.].
I answer that The cause of giving cannot be the cause of receiving, as neither can the cause of action be the cause of passion; yet it happens that one and the same person is giver and receiver, even as agent and patient, on account of different causes and from different points of view. Now tithes are due to the clergy as being ministers of the altar and sowers of spiritual things among the people. Wherefore those members of the clergy as such, i.e. as having ecclesiastical property, are not bound to pay tithes; whereas from some other cause through holding property in their own right, either by inheriting it from their kindred, or by purchase, or in any other similar manner, they are bound to the payment of tithes.

Reply to Objection: 1. Hence the Reply to the First Objection is clear, because the clergy like anyone else are bound to pay tithes on their own lands to the parish church, even though they be the clergy of that same church, because to possess a thing as one's private property is not the same as possessing it in common. But church lands are not tithable, even though they be within the boundaries of another parish.
2. Religious who are clerics, if they have care of souls, and dispense spiritual things to the people, are not bound to pay tithes, but they may receive them. Another reason applies to other religious, who though clerics do not dispense spiritual things to the people; for according to the ordinary law they are bound to pay tithes, but they are somewhat exempt by reason of various concessions granted by the Apostolic See [*Cap. Ex multiplici, Ex parte, and Ad audientiam, de Decimis, etc.].
3. In the Old Law first-fruits were due to the priests, and tithes to the Levites; and since the Levites were below the priests, the Lord commanded that the former should pay the high-priest "the tenth part of the tenth" [*Nb 18,26] instead of first-fruits: wherefore for the same reason the clergy are bound now to pay tithes to the Sovereign Pontiff, if he demanded them. For natural reason dictates that he who has charge of the common estate of a multitude should be provided with all goods, so that he may be able to carry out whatever is necessary for the common welfare.
4. Tithes should be employed for the assistance of the poor, through the dispensation of the clergy. Hence the poor have no reason for accepting tithes, but they are bound to pay them.

SERVICE BY PROMISE (Question [88])


We must now consider vows, whereby something is promised to God. Under this head there are twelve points of inquiry:

(1) What is a vow?

(2) What is the matter of a vow?

(3) Of the obligation of vows;

(4) Of the use of taking vows;

(5) Of what virtue is it an act?

(6) Whether it is more meritorious to do a thing from a vow, than without a vow?

(7) Of the solemnizing of a vow;

(8) Whether those who are under another's power can take vows?

(9) Whether children may be bound by vow to enter religion?

(10) Whether a vow is subject to dispensation or commutation?

(11) Whether a dispensation can be granted in a solemn vow of continence?

(12) Whether the authority of a superior is required in a dispensation from a vow?

Whether a vow consists in a mere purpose of the will?

Objection: 1. It would seem that a vow consists in nothing but a purpose of the will. According to some [*William of Auxerre, Sum. Aur. III, xxviii, qu. 1; Albertus Magnus, Sent. iv, D, 38], "a vow is a conception of a good purpose after a firm deliberation of the mind, whereby a man binds himself before God to do or not to do a certain thing." But the conception of a good purpose and so forth, may consist in a mere movement of the will. Therefore a vow consists in a mere purpose of the will.
2. Further, the very word vow seems to be derived from "voluntas" [will], for one is said to do a thing "proprio voto" [by one's own vow] when one does it voluntarily. Now to "purpose" is an act of the will, while to "promise" is an act of the reason. Therefore a vow consists in a mere act of the will.
3. Further, our Lord said (Lc 9,62): "No man putting his hand to the plough, and looking back, is fit for the kingdom of God." Now from the very fact that a man has a purpose of doing good, he puts his hand to the plough. Consequently, if he look back by desisting from his good purpose, he is not fit for the kingdom of God. Therefore by a mere good purpose a man is bound before God, even without making a promise; and consequently it would seem that a vow consists in a mere purpose of the will.

On the contrary It is written (Qo 5,3): "If thou hast vowed anything to God, defer not to pay it, for an unfaithful and foolish promise displeaseth Him." Therefore to vow is to promise, and a vow is a promise.
I answer that A vow denotes a binding to do or omit some particular thing. Now one man binds himself to another by means of a promise, which is an act of the reason to which faculty it belongs to direct. For just as a man by commanding or praying, directs, in a fashion, what others are to do for him, so by promising he directs what he himself is to do for another. Now a promise between man and man can only be expressed in words or any other outward signs; whereas a promise can be made to God by the mere inward thought, since according to 1S 16,7, "Man seeth those things that appear, but the Lord beholdeth the heart." Yet we express words outwardly sometimes, either to arouse ourselves, as was stated above with regard to prayer (Question [83], Article [12]), or to call others to witness, so that one may refrain from breaking the vow, not only through fear of God, but also through respect of men. Now a promise is the outcome from a purpose of doing something: and a purpose presupposes deliberation, since it is the act of a deliberate will. Accordingly three things are essential to a vow: the first is deliberation. the second is a purpose of the will; and the third is a promise, wherein is completed the nature of a vow. Sometimes, however, two other things are added as a sort of confirmation of the vow, namely, pronouncement by word of mouth, according to Ps 65,13, "I will pay Thee my vows which my lips have uttered"; and the witnessing of others. Hence the Master says (Sent. iv, D, 38) that a vow is "the witnessing of a spontaneous promise and ought to be made to God and about things relating to God": although the "witnessing" may strictly refer to the inward protestation.

Reply to Objection: 1. The conceiving of a good purpose is not confirmed by the deliberation of the mind, unless the deliberation lead to a promise.
2. Man's will moves the reason to promise something relating to things subject to his will, and a vow takes its name from the will forasmuch as it proceeds from the will as first mover.
3. He that puts his hand to the plough does something already; while he that merely purposes to do something does nothing so far. When, however, he promises, he already sets about doing, although he does not yet fulfil his promise: even so, he that puts his hand to the plough does not plough yet, nevertheless he stretches out his hand for the purpose of ploughing.

Whether a vow should always be about a better good?

Objection: 1. It would seem that a vow need not be always about a better good. A greater good is one that pertains to supererogation. But vows are not only about matters of supererogation, but also about matters of salvation: thus in Baptism men vow to renounce the devil and his pomps, and to keep the faith, as a gloss observes on Ps 75,12, "Vow ye, and pay to the Lord your God"; and Jacob vowed (Gn 28,21) that the Lord should be his God. Now this above all is necessary for salvation. Therefore vows are not only about a better good.
2. Further, Jephte is included among the saints (He 11,32). Yet he killed his innocent daughter on account of his vow (Jg 11). Since, then, the slaying of an innocent person is not a better good, but is in itself unlawful, it seems that a vow may be made not only about a better good, but also about something unlawful.
3. Further, things that tend to be harmful to the person, or that are quite useless, do not come under the head of a better good. Yet sometimes vows are made about immoderate vigils or fasts which tend to injure the person: and sometimes vows are about indifferent matters and such as are useful to no purpose. Therefore a vow is not always about a better good.

On the contrary It is written (Dt 23,22): "If thou wilt not promise thou shalt be without sin."
I answer that As stated above (Article [1]), a vow is a promise made to God. Now a promise is about something that one does voluntarily for someone else: since it would be not a promise but a threat to say that one would do something against someone. In like manner it would be futile to promise anyone something unacceptable to him. Wherefore, as every sin is against God, and since no work is acceptable to God unless it be virtuous, it follows that nothing unlawful or indifferent, but only some act of virtue, should be the matter of a vow. But as a vow denotes a voluntary promise, while necessity excludes voluntariness, whatever is absolutely necessary, whether to be or not to be, can nowise be the matter of a vow. For it would be foolish to vow that one would die or that one would not fly.On the other hand, if a thing be necessary. not absolutely but on the supposition of an end---for instance if salvation be unattainable without it---it may be the matter of a vow in so far as it is done voluntarily, but not in so far as there is a necessity for doing it. But that which is not necessary, neither absolutely, nor on the supposition of an end, is altogether voluntary, and therefore is most properly the matter of a vow. And this is said to be a greater good in comparison with that which is universally necessary for salvation. Therefore, properly speaking, a vow is said to be about a better good.

Reply to Objection: 1. Renouncing the devil's pomps and keeping the faith of Christ are the matter of baptismal vows, in so far as these things are done voluntarily, although they are necessary for salvation. The same answer applies to Jacob's vow: although it may also be explained that Jacob vowed that he would have the Lord for his God, by giving Him a special form of worship to which he was not bound, for instance by offering tithes and so forth as mentioned further on in the same passage.
2. Certain things are good, whatever be their result; such are acts of virtue, and these can be, absolutely speaking, the matter of a vow: some are evil, whatever their result may be; as those things which are sins in themselves, and these can nowise be the matter of a vow: while some, considered in themselves, are good, and as such may be the matter of a vow, yet they may have an evil result, in which case the vow must not be kept. It was thus with the vow of Jephte, who as related in Jg 11,30-31, "made a vow to the Lord, saying: If Thou wilt deliver the children of Ammon into my hands, whosoever shall first come forth out of the doors of my house, and shall meet me when I return in peace . . . the same will I offer a holocaust to the Lord." For this could have an evil result if, as indeed happened, he were to be met by some animal which it would be unlawful to sacrifice, such as an ass or a human being. Hence Jerome says [*Implicitly 1 Contra Jovin.: Comment. in Micheam vi, viii: Comment. in Jerem. vii. The quotation is from Peter Comestor, Hist. Scholast.]: "In vowing he was foolish, through lack of discretion, and in keeping his vow he was wicked." Yet it is premised (Jg 11,29) that "the Spirit of the Lord came upon him," because his faith and devotion, which moved him to make that vow, were from the Holy Ghost; and for this reason he is reckoned among the saints, as also by reason of the victory which he obtained, and because it is probable that he repented of his sinful deed, which nevertheless foreshadowed something good.
3. The mortification of one's own body, for instance by vigils and fasting, is not acceptable to God except in so far as it is an act of virtue; and this depends on its being done with due discretion, namely, that concupiscence be curbed without overburdening nature. on this condition such things may be the matter of a vow. Hence the Apostle after saying (Rm 12,1), "Present your bodies a living sacrifice, holy, pleasing to God," adds, "your reasonable service." Since, however, man is easily mistaken in judging of matters concerning himself, such vows as these are more fittingly kept or disregarded according to the judgment of a superior, yet so that, should a man find that without doubt he is seriously burdened by keeping such a vow, and should he be unable to appeal to his superior, he ought not to keep it. As to vows about vain and useless things they should be ridiculed rather than kept.

Summa Th. II-II EN Qu.87