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 ( Deut. 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 (Q[59], A[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.
Reply to Objection 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.
Reply to Objection 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.
Whether the seller is bound to state the defects of the thing sold?
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.
Objection 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.
Objection 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.
Objection 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.
Reply to Objection 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.
Reply to Objection 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.
Reply to Objection 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.
Whether, in trading, it is lawful to sell a thing at a higher price than what was paid for it?
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 Mat. 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.
Objection 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 (A[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.
Objection 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.