Summa Th. II-II EN Qu.77 a.2
Objection: 1. It would seem that a sale is not rendered unjust and unlawful through a fault in the thing sold. For less account should be taken of the other parts of a thing than of what belongs to its substance. Yet the sale of a thing does not seem to be rendered unlawful through a fault in its substance: for instance, if a man sell instead of the real metal, silver or gold produced by some chemical process, which is adapted to all the human uses for which silver and gold are necessary, for instance in the making of vessels and the like. Much less therefore will it be an unlawful sale if the thing be defective in other ways.
2. Further, any fault in the thing, affecting the quantity, would seem chiefly to be opposed to justice which consists in equality. Now quantity is known by being measured: and the measures of things that come into human use are not fixed, but in some places are greater, in others less, as the Philosopher states (Ethic. v, 7). Therefore just as it is impossible to avoid defects on the part of the thing sold, it seems that a sale is not rendered unlawful through the thing sold being defective.
3. Further, the thing sold is rendered defective by lacking a fitting quality. But in order to know the quality of a thing, much knowledge is required that is lacking in most buyers. Therefore a sale is not rendered unlawful by a fault (in the thing sold).
On the contrary Ambrose says (De Offic. iii, 11): "It is manifestly a rule of justice that a good man should not depart from the truth, nor inflict an unjust injury on anyone, nor have any connection with fraud."
I answer that A threefold fault may be found pertaining to the thing which is sold. One, in respect of the thing's substance: and if the seller be aware of a fault in the thing he is selling, he is guilty of a fraudulent sale, so that the sale is rendered unlawful. Hence we find it written against certain people (Is 1,22), "Thy silver is turned into dross, thy wine is mingled with water": because that which is mixed is defective in its substance.Another defect is in respect of quantity which is known by being measured: wherefore if anyone knowingly make use of a faulty measure in selling, he is guilty of fraud, and the sale is illicit. Hence it is written (Dt 25,13-14): "Thou shalt not have divers weights in thy bag, a greater and a less: neither shall there be in thy house a greater bushel and a less," and further on (Dt 25,16): "For the Lord . . . abhorreth him that doth these things, and He hateth all injustice."A third defect is on the part of the quality, for instance, if a man sell an unhealthy animal as being a healthy one: and if anyone do this knowingly he is guilty of a fraudulent sale, and the sale, in consequence, is illicit.In all these cases not only is the man guilty of a fraudulent sale, but he is also bound to restitution. But if any of the foregoing defects be in the thing sold, and he knows nothing about this, the seller does not sin, because he does that which is unjust materially, nor is his deed unjust, as shown above (Question [59], Article [2]). Nevertheless he is bound to compensate the buyer, when the defect comes to his knowledge. Moreover what has been said of the seller applies equally to the buyer. For sometimes it happens that the seller thinks his goods to be specifically of lower value, as when a man sells gold instead of copper, and then if the buyer be aware of this, he buys it unjustly and is bound to restitution: and the same applies to a defect in quantity as to a defect in quality.
Reply to Objection: 1. Gold and silver are costly not only on account of the usefulness of the vessels and other like things made from them, but also on account of the excellence and purity of their substance. Hence if the gold or silver produced by alchemists has not the true specific nature of gold and silver, the sale thereof is fraudulent and unjust, especially as real gold and silver can produce certain results by their natural action, which the counterfeit gold and silver of alchemists cannot produce. Thus the true metal has the property of making people joyful, and is helpful medicinally against certain maladies. Moreover real gold can be employed more frequently, and lasts longer in its condition of purity than counterfeit gold. If however real gold were to be produced by alchemy, it would not be unlawful to sell it for the genuine article, for nothing prevents art from employing certain natural causes for the production of natural and true effects, as Augustine says (De Trin. iii, 8) of things produced by the art of the demons.
2. The measures of salable commodities must needs be different in different places, on account of the difference of supply: because where there is greater abundance, the measures are wont to be larger. However in each place those who govern the state must determine the just measures of things salable, with due consideration for the conditions of place and time. Hence it is not lawful to disregard such measures as are established by public authority or custom.
3. As Augustine says (De Civ. Dei xi, 16) the price of things salable does not depend on their degree of nature, since at times a horse fetches a higher price than a slave; but it depends on their usefulness to man. Hence it is not necessary for the seller or buyer to be cognizant of the hidden qualities of the thing sold, but only of such as render the thing adapted to man's use, for instance, that the horse be strong, run well and so forth. Such qualities the seller and buyer can easily discover.
Objection: 1. It would seem that the seller is not bound to state the defects of the thing sold. Since the seller does not bind the buyer to buy, he would seem to leave it to him to judge of the goods offered for sale. Now judgment about a thing and knowledge of that thing belong to the same person. Therefore it does not seem imputable to the seller if the buyer be deceived in his judgment, and be hurried into buying a thing without carefully inquiring into its condition.
2. Further, it seems foolish for anyone to do what prevents him carrying out his work. But if a man states the defects of the goods he has for sale, he prevents their sale: wherefore Tully (De Offic. iii, 13) pictures a man as saying: "Could anything be more absurd than for a public crier, instructed by the owner, to cry: 'I offer this unhealthy horse for sale?'" Therefore the seller is not bound to state the defects of the thing sold.
3. Further, man needs more to know the road of virtue than to know the faults of things offered for sale. Now one is not bound to offer advice to all or to tell them the truth about matters pertaining to virtue, though one should not tell anyone what is false. Much less therefore is a seller bound to tell the faults of what he offers for sale, as though he were counseling the buyer.
4. Further, if one were bound to tell the faults of what one offers for sale, this would only be in order to lower the price. Now sometimes the price would be lowered for some other reason, without any defect in the thing sold: for instance, if the seller carry wheat to a place where wheat fetches a high price, knowing that many will come after him carrying wheat; because if the buyers knew this they would give a lower price. But apparently the seller need not give the buyer this information. Therefore, in like manner, neither need he tell him the faults of the goods he is selling.
On the contrary Ambrose says (De Offic. iii, 10): "In all contracts the defects of the salable commodity must be stated; and unless the seller make them known, although the buyer has already acquired a right to them, the contract is voided on account of the fraudulent action."
I answer that It is always unlawful to give anyone an occasion of danger or loss, although a man need not always give another the help or counsel which would be for his advantage in any way; but only in certain fixed cases, for instance when someone is subject to him, or when he is the only one who can assist him. Now the seller who offers goods for sale, gives the buyer an occasion of loss or danger, by the very fact that he offers him defective goods, if such defect may occasion loss or danger to the buyer---loss, if, by reason of this defect, the goods are of less value, and he takes nothing off the price on that account---danger, if this defect either hinder the use of the goods or render it hurtful, for instance, if a man sells a lame for a fleet horse, a tottering house for a safe one, rotten or poisonous food for wholesome. Wherefore if such like defects be hidden, and the seller does not make them known, the sale will be illicit and fraudulent, and the seller will be bound to compensation for the loss incurred.On the other hand, if the defect be manifest, for instance if a horse have but one eye, or if the goods though useless to the buyer, be useful to someone else, provided the seller take as much as he ought from the price, he is not bound to state the defect of the goods, since perhaps on account of that defect the buyer might want him to allow a greater rebate than he need. Wherefore the seller may look to his own indemnity, by withholding the defect of the goods.
Reply to Objection: 1. Judgment cannot be pronounced save on what is manifest: for "a man judges of what he knows" (Ethic. i, 3). Hence if the defects of the goods offered for sale be hidden, judgment of them is not sufficiently left with the buyer unless such defects be made known to him. The case would be different if the defects were manifest.
2. There is no need to publish beforehand by the public crier the defects of the goods one is offering for sale, because if he were to begin by announcing its defects, the bidders would be frightened to buy, through ignorance of other qualities that might render the thing good and serviceable. Such defect ought to be stated to each individual that offers to buy: and then he will be able to compare the various points one with the other, the good with the bad: for nothing prevents that which is defective in one respect being useful in many others.
3. Although a man is not bound strictly speaking to tell everyone the truth about matters pertaining to virtue, yet he is so bound in a case when, unless he tells the truth, his conduct would endanger another man in detriment to virtue: and so it is in this case.
4. The defect in a thing makes it of less value now than it seems to be: but in the case cited, the goods are expected to be of less value at a future time, on account of the arrival of other merchants, which was not foreseen by the buyers. Wherefore the seller, since he sells his goods at the price actually offered him, does not seem to act contrary to justice through not stating what is going to happen. If however he were to do so, or if he lowered his price, it would be exceedingly virtuous on his part: although he does not seem to be bound to do this as a debt of justice.
Objection: 1. It would seem that it is not lawful, in trading, to sell a thing for a higher price than we paid for it. For Chrysostom [*Hom. xxxviii in the Opus Imperfectum, falsely ascribed to St. John Chrysostom] says on Mt 21,12: "He that buys a thing in order that he may sell it, entire and unchanged, at a profit, is the trader who is cast out of God's temple." Cassiodorus speaks in the same sense in his commentary on Ps 70,15, "Because I have not known learning, or trading" according to another version [*The Septuagint]: "What is trade," says he, "but buying at a cheap price with the purpose of retailing at a higher price?" and he adds: "Such were the tradesmen whom Our Lord cast out of the temple." Now no man is cast out of the temple except for a sin. Therefore such like trading is sinful.
2. Further, it is contrary to justice to sell goods at a higher price than their worth, or to buy them for less than their value, as shown above (Article [1]). Now if you sell a thing for a higher price than you paid for it, you must either have bought it for less than its value, or sell it for more than its value. Therefore this cannot be done without sin.
3. Further, Jerome says (Ep ad Nepot. lii): "Shun, as you would the plague, a cleric who from being poor has become wealthy, or who, from being a nobody has become a celebrity." Now trading would net seem to be forbidden to clerics except on account of its sinfulness. Therefore it is a sin in trading, to buy at a low price and to sell at a higher price.
On the contrary Augustine commenting on Ps 70,15, "Because I have not known learning," [*Cf. OBJ 1] says: "The greedy tradesman blasphemes over his losses; he lies and perjures himself over the price of his wares. But these are vices of the man, not of the craft, which can be exercised without these vices." Therefore trading is not in itself unlawful.
I answer that A tradesman is one whose business consists in the exchange of things. According to the Philosopher (Polit. i, 3), exchange of things is twofold; one, natural as it were, and necessary, whereby one commodity is exchanged for another, or money taken in exchange for a commodity, in order to satisfy the needs of life. Such like trading, properly speaking, does not belong to tradesmen, but rather to housekeepers or civil servants who have to provide the household or the state with the necessaries of life. The other kind of exchange is either that of money for money, or of any commodity for money, not on account of the necessities of life, but for profit, and this kind of exchange, properly speaking, regards tradesmen, according to the Philosopher (Polit. i, 3). The former kind of exchange is commendable because it supplies a natural need: but the latter is justly deserving of blame, because, considered in itself, it satisfies the greed for gain, which knows no limit and tends to infinity. Hence trading, considered in itself, has a certain debasement attaching thereto, in so far as, by its very nature, it does not imply a virtuous or necessary end. Nevertheless gain which is the end of trading, though not implying, by its nature, anything virtuous or necessary, does not, in itself, connote anything sinful or contrary to virtue: wherefore nothing prevents gain from being directed to some necessary or even virtuous end, and thus trading becomes lawful. Thus, for instance, a man may intend the moderate gain which he seeks to acquire by trading for the upkeep of his household, or for the assistance of the needy: or again, a man may take to trade for some public advantage, for instance, lest his country lack the necessaries of life, and seek gain, not as an end, but as payment for his labor.
Reply to Objection: 1. The saying of Chrysostom refers to the trading which seeks gain as a last end. This is especially the case where a man sells something at a higher price without its undergoing any change. For if he sells at a higher price something that has changed for the better, he would seem to receive the reward of his labor. Nevertheless the gain itself may be lawfully intended, not as a last end, but for the sake of some other end which is necessary or virtuous, as stated above.
2. Not everyone that sells at a higher price than he bought is a tradesman, but only he who buys that he may sell at a profit. If, on the contrary, he buys not for sale but for possession, and afterwards, for some reason wishes to sell, it is not a trade transaction even if he sell at a profit. For he may lawfully do this, either because he has bettered the thing, or because the value of the thing has changed with the change of place or time, or on account of the danger he incurs in transferring the thing from one place to another, or again in having it carried by another. In this sense neither buying nor selling is unjust.
3. Clerics should abstain not only from things that are evil in themselves, but even from those that have an appearance of evil. This happens in trading, both because it is directed to worldly gain, which clerics should despise, and because trading is open to so many vices, since "a merchant is hardly free from sins of the lips" [*'A merchant is hardly free from negligence, and a huckster shall not be justified from the sins of the lips'] (Si 26,28). There is also another reason, because trading engages the mind too much with worldly cares, and consequently withdraws it from spiritual cares; wherefore the Apostle says (2Tm 2,4): "No man being a soldier to God entangleth himself with secular businesses." Nevertheless it is lawful for clerics to engage in the first mentioned kind of exchange, which is directed to supply the necessaries of life, either by buying or by selling.
We must now consider the sin of usury, which is committed in loans: and under this head there are four points of inquiry:
(1) Whether it is a sin to take money as a price for money lent, which is to receive usury?
(2) Whether it is lawful to lend money for any other kind of consideration, by way of payment for the loan?
(3) Whether a man is bound to restore just gains derived from money taken in usury?
(4) Whether it is lawful to borrow money under a condition of usury?
Objection: 1. It would seem that it is not a sin to take usury for money lent. For no man sins through following the example of Christ. But Our Lord said of Himself (Lc 19,23): "At My coming I might have exacted it," i.e. the money lent, "with usury." Therefore it is not a sin to take usury for lending money.
2. Further, according to Ps 18,8, "The law of the Lord is unspotted," because, to wit, it forbids sin. Now usury of a kind is allowed in the Divine law, according to Dt 23,19-20: "Thou shalt not fenerate to thy brother money, nor corn, nor any other thing, but to the stranger": nay more, it is even promised as a reward for the observance of the Law, according to Dt 28,12: "Thou shalt fenerate* to many nations, and shalt not borrow of any one." [*'Faeneraberis'---'Thou shalt lend upon usury.' The Douay version has simply 'lend.' The objection lays stress on the word 'faeneraberis': hence the necessity of rendering it by 'fenerate.'] Therefore it is not a sin to take usury.
3. Further, in human affairs justice is determined by civil laws. Now civil law allows usury to be taken. Therefore it seems to be lawful.
4. Further, the counsels are not binding under sin. But, among other counsels we find (Lc 6,35): "Lend, hoping for nothing thereby." Therefore it is not a sin to take usury.
5. Further, it does not seem to be in itself sinful to accept a price for doing what one is not bound to do. But one who has money is not bound in every case to lend it to his neighbor. Therefore it is lawful for him sometimes to accept a price for lending it.
6. Further, silver made into coins does not differ specifically from silver made into a vessel. But it is lawful to accept a price for the loan of a silver vessel. Therefore it is also lawful to accept a price for the loan of a silver coin. Therefore usury is not in itself a sin.
7. Further, anyone may lawfully accept a thing which its owner freely gives him. Now he who accepts the loan, freely gives the usury. Therefore he who lends may lawfully take the usury.
On the contrary It is written (Ex 22,25): "If thou lend money to any of thy people that is poor, that dwelleth with thee, thou shalt not be hard upon them as an extortioner, nor oppress them with usuries."
I answer that To take usury for money lent is unjust in itself, because this is to sell what does not exist, and this evidently leads to inequality which is contrary to justice. In order to make this evident, we must observe that there are certain things the use of which consists in their consumption: thus we consume wine when we use it for drink and we consume wheat when we use it for food. Wherefore in such like things the use of the thing must not be reckoned apart from the thing itself, and whoever is granted the use of the thing, is granted the thing itself and for this reason, to lend things of this kin is to transfer the ownership. Accordingly if a man wanted to sell wine separately from the use of the wine, he would be selling the same thing twice, or he would be selling what does not exist, wherefore he would evidently commit a sin of injustice. In like manner he commits an injustice who lends wine or wheat, and asks for double payment, viz. one, the return of the thing in equal measure, the other, the price of the use, which is called usury.On the other hand, there are things the use of which does not consist in their consumption: thus to use a house is to dwell in it, not to destroy it. Wherefore in such things both may be granted: for instance, one man may hand over to another the ownership of his house while reserving to himself the use of it for a time, or vice versa, he may grant the use of the house, while retaining the ownership. For this reason a man may lawfully make a charge for the use of his house, and, besides this, revendicate the house from the person to whom he has granted its use, as happens in renting and letting a house.Now money, according to the Philosopher (Ethic. v, 5; Polit. i, 3) was invented chiefly for the purpose of exchange: and consequently the proper and principal use of money is its consumption or alienation whereby it is sunk in exchange. Hence it is by its very nature unlawful to take payment for the use of money lent, which payment is known as usury: and just as a man is bound to restore other ill-gotten goods, so is he bound to restore the money which he has taken in usury.
Reply to Objection: 1. In this passage usury must be taken figuratively for the increase of spiritual goods which God exacts from us, for He wishes us ever to advance in the goods which we receive from Him: and this is for our own profit not for His.
2. The Jews were forbidden to take usury from their brethren, i.e. from other Jews. By this we are given to understand that to take usury from any man is evil simply, because we ought to treat every man as our neighbor and brother, especially in the state of the Gospel, whereto all are called. Hence it is said without any distinction in Ps 14,5: "He that hath not put out his money to usury," and (Ez 18,8): "Who hath not taken usury [*Vulg.: 'If a man . . . hath not lent upon money, nor taken any increase . . . he is just.']." They were permitted, however, to take usury from foreigners, not as though it were lawful, but in order to avoid a greater evil, lest, to wit, through avarice to which they were prone according to Is 56,11, they should take usury from the Jews who were worshippers of God.Where we find it promised to them as a reward, "Thou shalt fenerate to many nations," etc., fenerating is to be taken in a broad sense for lending, as in Si 29,10, where we read: "Many have refused to fenerate, not out of wickedness," i.e. they would not lend. Accordingly the Jews are promised in reward an abundance of wealth, so that they would be able to lend to others.
3. Human laws leave certain things unpunished, on account of the condition of those who are imperfect, and who would be deprived of many advantages, if all sins were strictly forbidden and punishments appointed for them. Wherefore human law has permitted usury, not that it looks upon usury as harmonizing with justice, but lest the advantage of many should be hindered. Hence it is that in civil law [*Inst. II, iv, de Usufructu] it is stated that "those things according to natural reason and civil law which are consumed by being used, do not admit of usufruct," and that "the senate did not (nor could it) appoint a usufruct to such things, but established a quasi-usufruct," namely by permitting usury. Moreover the Philosopher, led by natural reason, says (Polit. i, 3) that "to make money by usury is exceedingly unnatural."
4. A man is not always bound to lend, and for this reason it is placed among the counsels. Yet it is a matter of precept not to seek profit by lending: although it may be called a matter of counsel in comparison with the maxims of the Pharisees, who deemed some kinds of usury to be lawful, just as love of one's enemies is a matter of counsel. Or again, He speaks here not of the hope of usurious gain, but of the hope which is put in man. For we ought not to lend or do any good deed through hope in man, but only through hope in God.
5. He that is not bound to lend, may accept repayment for what he has done, but he must not exact more. Now he is repaid according to equality of justice if he is repaid as much as he lent. Wherefore if he exacts more for the usufruct of a thing which has no other use but the consumption of its substance, he exacts a price of something non-existent: and so his exaction is unjust.
6. The principal use of a silver vessel is not its consumption, and so one may lawfully sell its use while retaining one's ownership of it. On the other hand the principal use of silver money is sinking it in exchange, so that it is not lawful to sell its use and at the same time expect the restitution of the amount lent. It must be observed, however, that the secondary use of silver vessels may be an exchange, and such use may not be lawfully sold. In like manner there may be some secondary use of silver money; for instance, a man might lend coins for show, or to be used as security.
7. He who gives usury does not give it voluntarily simply, but under a certain necessity, in so far as he needs to borrow money which the owner is unwilling to lend without usury.
Objection: 1. It would seem that one may ask for some other kind of consideration for money lent. For everyone may lawfully seek to indemnify himself. Now sometimes a man suffers loss through lending money. Therefore he may lawfully ask for or even exact something else besides the money lent.
2. Further, as stated in Ethic. v, 5, one is in duty bound by a point of honor, to repay anyone who has done us a favor. Now to lend money to one who is in straits is to do him a favor for which he should be grateful. Therefore the recipient of a loan, is bound by a natural debt to repay something. Now it does not seem unlawful to bind oneself to an obligation of the natural law. Therefore it is not unlawful, in lending money to anyone, to demand some sort of compensation as condition of the loan.
3. Further, just as there is real remuneration, so is there verbal remuneration, and remuneration by service, as a gloss says on Is 33,15, "Blessed is he that shaketh his hands from all bribes [*Vulg.: 'Which of you shall dwell with everlasting burnings? . . . He that shaketh his hands from all bribes.']." Now it is lawful to accept service or praise from one to whom one has lent money. Therefore in like manner it is lawful to accept any other kind of remuneration.
4. Further, seemingly the relation of gift to gift is the same as of loan to loan. But it is lawful to accept money for money given. Therefore it is lawful to accept repayment by loan in return for a loan granted.
5. Further, the lender, by transferring his ownership of a sum of money removes the money further from himself than he who entrusts it to a merchant or craftsman. Now it is lawful to receive interest for money entrusted to a merchant or craftsman. Therefore it is also lawful to receive interest for money lent.
6. Further, a man may accept a pledge for money lent, the use of which pledge he might sell for a price: as when a man mortgages his land or the house wherein he dwells. Therefore it is lawful to receive interest for money lent.
7. Further, it sometimes happens that a man raises the price of his goods under guise of loan, or buys another's goods at a low figure; or raises his price through delay in being paid, and lowers his price that he may be paid the sooner. Now in all these cases there seems to be payment for a loan of money: nor does it appear to be manifestly illicit. Therefore it seems to be lawful to expect or exact some consideration for money lent.
On the contrary Among other conditions requisite in a just man it is stated (Ez 18,17) that he "hath not taken usury and increase."
I answer that According to the Philosopher (Ethic. iv, 1), a thing is reckoned as money "if its value can be measured by money." Consequently, just as it is a sin against justice, to take money, by tacit or express agreement, in return for lending money or anything else that is consumed by being used, so also is it a like sin, by tacit or express agreement to receive anything whose price can be measured by money. Yet there would be no sin in receiving something of the kind, not as exacting it, nor yet as though it were due on account of some agreement tacit or expressed, but as a gratuity: since, even before lending the money, one could accept a gratuity, nor is one in a worse condition through lending.On the other hand it is lawful to exact compensation for a loan, in respect of such things as are not appreciated by a measure of money, for instance, benevolence, and love for the lender, and so forth.
Reply to Objection: 1. A lender may without sin enter an agreement with the borrower for compensation for the loss he incurs of something he ought to have, for this is not to sell the use of money but to avoid a loss. It may also happen that the borrower avoids a greater loss than the lender incurs, wherefore the borrower may repay the lender with what he has gained. But the lender cannot enter an agreement for compensation, through the fact that he makes no profit out of his money: because he must not sell that which he has not yet and may be prevented in many ways from having.
2. Repayment for a favor may be made in two ways. In one way, as a debt of justice; and to such a debt a man may be bound by a fixed contract; and its amount is measured according to the favor received. Wherefore the borrower of money or any such thing the use of which is its consumption is not bound to repay more than he received in loan: and consequently it is against justice if he be obliged to pay back more. In another way a man's obligation to repayment for favor received is based on a debt of friendship, and the nature of this debt depends more on the feeling with which the favor was conferred than on the greatness of the favor itself. This debt does not carry with it a civil obligation, involving a kind of necessity that would exclude the spontaneous nature of such a repayment.
3. If a man were, in return for money lent, as though there had been an agreement tacit or expressed, to expect or exact repayment in the shape of some remuneration of service or words, it would be the same as if he expected or exacted some real remuneration, because both can be priced at a money value, as may be seen in the case of those who offer for hire the labor which they exercise by work or by tongue. If on the other hand the remuneration by service or words be given not as an obligation, but as a favor, which is not to be appreciated at a money value, it is lawful to take, exact, and expect it.
4. Money cannot be sold for a greater sum than the amount lent, which has to be paid back: nor should the loan be made with a demand or expectation of aught else but of a feeling of benevolence which cannot be priced at a pecuniary value, and which can be the basis of a spontaneous loan. Now the obligation to lend in return at some future time is repugnant to such a feeling, because again an obligation of this kind has its pecuniary value. Consequently it is lawful for the lender to borrow something else at the same time, but it is unlawful for him to bind the borrower to grant him a loan at some future time.
5. He who lends money transfers the ownership of the money to the borrower. Hence the borrower holds the money at his own risk and is bound to pay it all back: wherefore the lender must not exact more. On the other hand he that entrusts his money to a merchant or craftsman so as to form a kind of society, does not transfer the ownership of his money to them, for it remains his, so that at his risk the merchant speculates with it, or the craftsman uses it for his craft, and consequently he may lawfully demand as something belonging to him, part of the profits derived from his money.
6. If a man in return for money lent to him pledges something that can be valued at a price, the lender must allow for the use of that thing towards the repayment of the loan. Else if he wishes the gratuitous use of that thing in addition to repayment, it is the same as if he took money for lending, and that is usury, unless perhaps it were such a thing as friends are wont to lend to one another gratis, as in the case of the loan of a book.
7. If a man wish to sell his goods at a higher price than that which is just, so that he may wait for the buyer to pay, it is manifestly a case of usury: because this waiting for the payment of the price has the character of a loan, so that whatever he demands beyond the just price in consideration of this delay, is like a price for a loan, which pertains to usury. In like manner if a buyer wishes to buy goods at a lower price than what is just, for the reason that he pays for the goods before they can be delivered, it is a sin of usury; because again this anticipated payment of money has the character of a loan, the price of which is the rebate on the just price of the goods sold. On the other hand if a man wishes to allow a rebate on the just price in order that he may have his money sooner, he is not guilty of the sin of usury.
Summa Th. II-II EN Qu.77 a.2