Rambam - 3 Chapters a Day

I.e., he threatened his life itself.

A sale is dependent on the seller’s consent. Nevertheless, if he issued such consent, even if he was compelled to do so, it is binding and the sale is considered to be unalterable.
In his gloss on Halachah 8, the Maggid Mishneh states that this principle applies with regard to a sale, but not to a gift.

See Shulchan Aruch (Choshen Mishpat 205:4), which discusses whether there is a difference between landed property and movable property if the person does not pay the entire worth of the object that he takes.

But made an admission to witnesses that he took the funds in exchange for the field.
The Ra’avad and the Tur (Choshen Mishpat 205) maintain that for this law to apply, it is necessary for the witnesses to see the money pass hands. The Shulchan Aruch (Choshen Mishpat 205:1) quotes the Rambam’s view, while the Ramah follows that of the Tur.

Since the sale is dependent on the will of the seller, if he makes an explicit statement to the fact that the sale is against his will, the sale is nullified.

Our translation is somewhat loose. Sefer Me’irat Einayim 205:6 offers two explanations for the term moda’ah:
a) information - the seller informs the witnesses of the factors compelling him to sell;
b) suffering - he notifies them that he is undergoing suffering and he is therefore selling the property.

Ordinarily possession is considered to be proof of ownership of movable property immediately, and of landed property after three years. Nevertheless, these principles do not apply with regard to a thief. He is never considered to be the legitimate owner.

They need not know in which manner he is being compelled against his will (Beit Yosef, Choshen Mishpat 205).

I.e., a person came with a claim and the defendant denied it, and rather than engage in a protracted dispute, each agreed to forgo a portion of their claim.

For he is not receiving anything in return. Therefore, even though we do not see that he is being compelled against his will, since he does not desire to give up his ownership of the article being given as a gift, it remains his property.
With regard to a sale or a compromise, by contrast, even if the seller originally protested, since he is receiving money for the sale or avoiding difficulty by the compromise, we assume that he agreed unless it is obvious that he is under compulsion.

See Hilchot Zechiyah UMatanah 5:4, where this concept is explained in depth.

For like a person giving a gift, the creditor does not receive anything in exchange for his gesture of good-will.

The Ramah (Choshen Mishpat 205:7) cites an opinion that states that mere threats are not considered compulsion. For people realize that at times people make threats without carrying them out.

I.e., as the Rambam continues to explain, we are not speaking only of physical compulsion, but also about financial compulsion. Similarly, blackmail concerning one’s reputation could also be considered a relevant factor.

I.e., the rental contract; the commentaries question the use of this wording.

This time period is significant. As the Rambam explains (Hilchot To’en V’Nit’an 11:1-2), after landed property has been in a person’s possession for three years, we accept his claim that he purchased it although he cannot present a bill of sale showing that he acquired it from the previous owner.

Since the tenant had been in possession of the field for three years, his claim would be accepted by the court.

I.e., the danger of denial was not merely a potential, but was actually brought into expression in court.

Telling the witnesses of the threat the tenant made.

From the Rambam’s words, it would appear that the same witnesses must be aware of the compulsion and hear the protest. The Maggid Mishneh, however, explains that as long as a protest is issued before the sale, it is effective, even if the seller proves he was acting under compulsion through other witnesses.

I.e., when is a protest necessary?

Chamas, the root of chamsan, denotes crime, injustice, violence and outrage. The Maggid Mishneh explains that if the seller willingly accepted the money that he was offered, despite the fact that originally he was forced to sell against his will, the purchaser is not considered a chamsan. Only when the seller desires to protest is the title applied to the purchaser. Despite the fact that he pays, he is still considered to be acting criminally.

I.e., it became public knowledge that the robber had taken the field from its rightful owner.

In Hilchot Gezelah 9:14-16, the Rambam writes:
[The following rules apply when a person] obtains a field by robbery, and after it was established that his intent was to take it by robbery, he then purchases it from the original owner. If the [original] owner claims: “I was acting under coercion at the time that I sold it to him. I sold it to him against my will, because he was a robber,” the robber does not acquire [the field], even though there are witnesses that he purchased [the field] in their presence. Instead, the field should be restored to its [original] owner and the robber should be given back the money that he paid....
The owner of the field does not have to issue a protest over the sale in such an instance, for it has been established that the field was taken by robbery, and any proof of ownership brought by the robber is not accepted.
The Ra’avad, Rabbenu Asher, the Tur and the Ramah (Choshen Mishpat 151:3) differ with the Rambam’s decision in Hilchot Gezelah. They maintain that if the witnesses to the sale saw the robber give the owner money and the owner does not issue a protest, the sale is binding.
In his Kessef Mishneh, Rav Yosef Karo explains the Rambam’s decision, stating that it depends on the distinction between a person who was already established as having taken a field by robbery, and other instances when a person was compelled to sell a field against his will. And in his Shulchan Aruch (Choshen Mishpat 151:3, 205:8) he quotes the Rambam’s words.

I.e., we do not say that their signature indicates that the seller voluntarily consented to the sale.
Ordinarily witnesses cannot give testimony that negates a legal document that they signed. Nevertheless, in this instance, the protest that they signed precedes their signature on the deed of sale. Therefore, it is acceptable.

Instead, we assume that the robber took the field without paying for it and compelled the former owner to say that not only did he sell it willingly, but he received money as well.

For then it is obvious that money was in fact paid for the property. It should be returned to the robber.

I.e., the seller’s present statements indicate that he is willing to carry on with the sale. The Maggid Mishneh and the Kessel Mishneh emphasize that even if the seller is compelled to nullify the protests under duress, the nullification is binding. Just as a sale made under duress is binding, a nullification made under duress is binding. The only alternative is to issue a protest against the nullification, as the Rambam continues to explain.
See also Hilchot Gerushin 6:20, where the Rambam speaks about the potential to issue a protest against a bill of divorce. That protest can be nullified in the following manner:
The witnesses should tell [the husband] before the composition of the get: “Affirm in our presence that any statements that you have made which, when verified, would cause [this] get to be nullified, are themselves nullified.” [The husband] must answer “Yes.”

The Kessef Mishneh notes that in Chapter 5, Halachah II, the Rambam writes that a kinyan has no effect with regard to the nullification of a protest. He explains, however, that, as the Rambam explains in Chapter 5, Halachah 13, the kinyan is effective in demonstrating that the person is not making the statements facetiously and genuinely desires to nullify the protests.

I.e., the protest he issued against the nullification of the protests is heeded. Despite the fact that he said he wished to nullify his protest, we assume that the statement is being made against his will.
The Rambam’s words are quoted by the Shulchan Aruch (Choshen Mishpat 205:11). The Tur and the Ramah maintain that even in such a situation if one explicitly states that one negates all protests, the protests are nullified. See also Sefer Me’irat Einayim 205:27, which quotes the suggestion of the Rashba, who states that one can nullify the protests by stating that one disqualifies the witnesses before whom one issued the protests.

In Hilchot Ishut 6:7, the Rambam gives as an example for this principle, the condition: “If you ascend to the heavens you will be consecrated to me; if you do not, you will not be consecrated to me.”
In Hilchot Ishut, the Rambam mentions this principle as one of the requirements for conditional agreements. Perhaps the reason he singles out this requirement here is because it is relevant to the bulk of the chapter, which deals with the concept of asmachta.

In Chapter 6 of those halachot, the Rambam lists and explains four requirements necessary for conditional agreements:
a) the condition must be repeated in both a positive and a negative manner: “If you do such and such, the transaction is binding; if you do not do such and such, the transaction is not binding;
b) the positive dimension of the condition must be stated before the negative one, as in the above example;
c) the conditional agreement must be made before the transaction is made; if a transaction is completed, and then one of the parties wishes to attach a conditional agreement, the condition is not binding;
d) the condition must be possible to be fulfilled as above;
See also Hilchot Zechiyah UMatanah 3:6-7.
There are opinions that maintain that with regard to financial matters, there is no necessity to repeat the condition. The Rambam mentions this point in Hilchot Ishut 6:14 and Hilchot Zechiyah 3:6, and attempts to negate that argument, explaining that the source for the laws of conditional agreements is the agreement reached between Moses and the tribes of Gad and Reuven. That was an agreement concerning financial matters. The Rambam’s opinion, however, is not accepted by all authorities.

That the condition and the transaction are binding.

As reflected in the halachot that follow, the seller must say al menat, “on the condition that,” or k’neh me’achshav, “Acquire it retroactively from the present time,” when stating the condition.

Even if the purchaser performs a kinyan after fulfilling the condition, the ownership of the article is not transferred, as the Rambam states in the following halachah.
The Rambam’s decision depends on his understanding of Bava Metzia 66b. Others interpret that passage differently, as noted by the Maggid Mishneh. Because of the difference of opinion regarding the matter, the Shulchan Aruch (Choshen Mishpat 207:2) quotes the Rambam’s words with the preface of the phrase “There are those who say.” See also the notes on Halachah 4.

The root of the word asmachta, is the word samoch, which means “depend on.” The intent is that the owner did not make a hard and fast decision to transfer ownership, but rather his decision was dependent on an external factor that was unclarified. As such, the statements he made are not binding.

I.e., he performs a kinyan that transfers ownership of the house.

The acquisition takes places retroactively.

The Maggid Mishneh states that the Ramban differs with the Rambam and states that if the condition is dependent on the actions of another person, the seller is considered to have made a binding commitment. For he realizes that the other person’s actions are not dependent on his own will. As support, he cites the conditional agreement made by Moses with the tribes of Gad and Reuven.
The Machaneh Efrayim justifies the Rambam’s opinion, explaining that even if the condition is left up to the will of another person, the agreement is considered an asmachta. The reason the agreement with the tribes of Gad and Reuven was not considered an asmachta was that these tribes took possession of the land they desired at the time the agreement was made.

Nor does he acquire the property if he manifests his ownership over it before he fulfills the condition. For at that time, the owner has not yet agreed to transfer the property to him.

Sefer Me’irat Einayim 207:6 explains the difference between a conditional agreement and an asmachta as follows: With regard to a conditional agreement, the transaction is of fundamental importance, and the condition is added on as a secondary dimension. With regard to an asmachta, by contrast, it is the condition that is of primary importance. Just in order to motivate the other person to fulfill that condition, it was necessary to promise him that the transaction would be fulfilled. Thus, the owner never really had the intent of performing the transaction, and thus he never transferred ownership.

See, however, Halachah 13, which states that if the person made the stipulation in front of a prominent court and affirmed it with a kinyan, it is binding.

As reflected· in the gloss of the Kessef Mishneh, the Rambam’s ruling applies only when the security is movable property. If it is landed property, even the Rambam would agree that it remains the property of its original owner.

To guarantee that he will pay him for an article that he seeks to purchase.

The commentaries [see the ruling of the Ramah (Choshen Mishpat 207:13)] differentiate between a condition that is an obvious exaggeration, and a condition that reflects a correct appreciation of the loss involved. For example, if a sharecropper says: “If I do not work the field, I will pay you 1000 zuz,” it is clear that he is exaggerating and is not undertaking a serious commitment. If, however, he says: “If I do not work the field, I will reimburse you for the loss,” his commitment is binding. The Rambam himself quotes this law in Hilchot Sechirut 8:13.

The Ra’avad and the Tur (Choshen Mishpat 207) differ with the Rambam with regard to this issue. The Rambam’s decision is based on a passage in Bava Metzia 48b and 77b that appears to indicate that once security has been entrusted to another person, the person who entrusted it has willfully undertaken the risk of its being kept. Therefore, it is not considered an asmachta.
The Ra’avad and the Tur, by contrast, explain that although he entrusted the security to a colleague, the person never really thought about forgoing it. Therefore, the agreement is considered as an asmachta.
The Shulchan Aruch (Choshen Mishpat 207:11) quotes the Rambam’s view, while the Ramah cites the other opinions.

I.e., he made it facetiously, without sincerely considering whether or not he would have to pay.

I.e., the debtor feared that if the promissory note remained in the creditor’s possession, he would demand payment of the entire debt. Therefore, he requested that he entrust it to a third party. The creditor agreed to do so, but only if the debtor made the stipulation cited by the Rambam.

I.e., and thus allow the creditor to sue for the entire amount.

Since the creditor is not in possession of the promissory note, even the Rambam would agree that the debtor made the commitment without seriously considering the possibility that he might be required to pay the additional amount. If, however, the promissory note was in the possession of the creditor, and the debtor made a similar stipulation, the Maggid Mishneh maintains that the Rambam would consider it binding. Since the promissory note was in the possession of the creditor - like the security mentioned in the previous halachah - the debtor would not make a statement totally facetiously.

Rabbah expresses this concept succinctly (Bava Metzia 66b): “Whenever ‘if’ is mentioned, the transaction is not binding.”

Thus, at no time did he make a binding commitment to transfer ownership of the article.

There are opinions that maintain that whenever a person says al menat, “on the condition that,” it is considered as if he said me’achshav, “[retroactive] to the present time.” This ruling is, however, not accepted by all authorities. See Ramah (Choshen Mishpat 207:14).

See an expression of this concept in Hilchot Malveh V’Loveh 6:4.

The Rambam and similarly, the Shulchan Aruch (Choshen Mishpat 207:14), state the condition using positive terminology. The Tur, however, states “If I do not come.... “See Sefer Me’irat Einayim 207:36 for a discussion of this distinction.

I.e., the object of the transaction must be explicitly specified (Sefer Me’irat Einayim 207:37).

The Ramah (loc. cit.) states that there are opinions that maintain that this kinyan must be made in the presence of a prominent court. (See Halachah 13.)

I.e., makes a verbal statement to that effect, although he does not specify it as a condition to the sale. Note the contrast to the following halachah.

If, however, he makes these statements before or after the time the transaction is completed, they are of no consequence. [See Maggid Mishneh; Shulchan Aruch (Choshen Mishpat 207:4).]

The Kessef Mishneh explains that this ruling is based on the· following rationale: A person would not sell property that provides him with an income unless he were intending to move. Based on this logic, he explains that these laws do not apply with regard to movable property. For movable property is often sold even when one does not consider changing one’s locale. The Ramah (Choshen Mishpat 207:3) includes this concept in his gloss on the Shulchan Aruch.

Sefer Me’irat Einayim 207:8 emphasizes that the factors preventing the person may be external - thieves and brigands on the roads - or internal - illness.

The Maggid Mishneh states that this law applies only when the seller is prevented from making the journey or purchasing the wheat by factors beyond his control. If he changes his mind and does not make the journey or the purchase for other reasons, the sale is not nullified.

The Ramah (Choshen Mishpat 207:4) states that if it is blatantly obvious that the sale was made only for a specific intent, and the person was prevented from fulfilling that intent by forces beyond his control, the sale is not binding.

And the entity reverts to its original owner.

This addition is necessary, as evident from a comparison to the following halachah.

See Chapter 23, Halachah 5. Throughout the entire time the article is in the possession of the purchaser, he is entitled to benefit from it, and that benefit is not considered to be interest. The difference between this instance and that described in the following halachah is that in this instance, a time span has been set for the purchase. Thus, it resembles a present that is given with the stipulation that it be returned (Sefer Me’irat Einayim 207:11).

According to many commentaries, the same ruling would apply if the stipulation is made by the purchaser. It is just far more likely that the seller would be the one making the stipulation. Note, however, the second interpretation of the Kessef Mishneh mentioned below.

Before the sale was completed.

And repay you for the field.

The purchaser paid money for the field and received his money in return. It thus resembles a loan. If the purchaser derived benefit from the produce, it would resemble an increment on his money. Thus, although a sale is involved, it is considered to be interest forbidden by Scriptural Law. (See Hilchot Malveh V’Loveh 6:5. Significantly, in that ruling the Rambam says that the transaction is not binding, while here he does not make such a statement.)

The Tur (Choshen Mishpat 207) objects to the Rambam’s decision, considering it paradoxical that on one hand, the Rambam considers the purchaser bound to fulfill the condition, and yet entitled to receive benefit from the land. He interprets Bava Metzia 65b, the source for this halachah, as implying that the purchaser’s statements are facetious and not binding.
The Kessef Mishneh offers two resolutions to these difficulties:
a) The condition was added after the sale was completed. Since under the terms of the sale itself, the purchaser had no obligation to return the field, the benefit he receives from the field cannot be compared to interest paid on a loan. His obligation to return the field is thus considered to be a new matter, unrelated to the benefit he receives.
b) The first clause refers to a condition made by the seller; the second to one established by the purchaser. In both instances, the condition was made before the sale was concluded. Nevertheless, in the first instance, since the lender made the condition and the matter of returning the loan is dependent on him, it is considered comparable to taking a loan and paying interest. When the condition is made by the purchaser, it is not at all like a loan. For he has no way of knowing or ensuring that his money will in fact be returned. Everything is dependent on the seller.

I.e., the seller wanted to make this a condition of the sale.

I.e., the sale of the field to the woman was not binding.

He did not make a binding commitment to return the field.

In his Commentary on the Mishnah (Bava Batra 10:5), the Rambam defines “a prominent court” as a court made up of judges who possess the special semichah (“ordination”) conveyed from judge to judge in a chain going back to Moses. Since from the era of the Talmud onward, there were no judges who possess such semichah, such a definition would make this halachah irrelevant.
Significantly, the Maggid Mishneh differs and quotes the Rashba as interpreting “a prominent court” as not referring to a court of judges with semichah, but rather a court that is commonly accepted as authoritative, and which has the right to expropriate money. The Ramah (Choshen Mishpat 207:15) mentions that view, but also that of the Tur, which maintains that as long as the court is knowledgeable with regard to the laws of asmachta’ot, it is considered to be “a prominent court.”

The Rambam’s words have attracted the attention of the commentaries, for it would seem that since a kinyan has been concluded, it would not be necessary to entrust the record to a court for it to be binding. For a kinyan is ordinarily effective me’achshav, retroactive to the time of the kinyan. And as stated in Halachah 7, whenever a stipulation is made that is effectively retroactive to the time of the stipulation, it is binding.
The Maggid Mishneh and the Kessef Mishneh explain that this is a unique instance, because the stipulation is being imposed upon him by the court; he is not making the stipulation himself. Therefore, if the document had not been entrusted to a court, it would not have been binding. Alternatively, it can be explained that this is speaking about a kinyan that is not effective me’achshav. For in this instance, the kinyan is instituted only to show the seriousness of the person’s intent, and not for any practical purpose. (See also Halachah 18 and the gloss of the Maggid Mislmeh on that halachah with regard to an asmachta that would not be binding although a kinyan is being made.)

As illustrated in the following halachah.
The Ramah (Choshen Mishpat 207:15) cites the view of Rabbenu Asher, who states that since the kinyan was made in a prominent court, it is not necessary to entrust one’s legal documents to the court.

Bava Batra 149a makes this statement, explaining how a convert named Isar could have transferred money before his death.

Since he did not make the gift conditional on any stipulation, we assume that he made the commitment wholeheartedly. Hence, it is binding (Sefer Me’irat Einayim 207:58).

See Hilchot To’en V’Nit’an 7:1 which explains that if a person does not charge the witnesses in this manner, he is not liable. For he can explain that he was speaking facetiously when he made the commitment, or made the statements only so that he would not appear wealthy.

See the Maggid Mishneh and Sefer Me’irat Einayim 40:1, who explain that the Ramban, the Rashba and the Tur do not agree with the Rambam on this clause. Sefer Me’irat Einayim questions why Rav Yosef Karo and the Ramah accept the Rambam’s view without mentioning the opinions that differ.

As stated in Hilchot Malveh V’Loveh 11:3, the obligation created by such a legal document is comparable only to that of a loan supported by a verbal commitment; it is not comparable to an ordinary promissory note. Nevertheless, it is sufficient to bind the giver to keep his word.

I.e., just as a guarantor accepts an obligation upon himself although he did not receive anything from the lender, so too, this person becomes bound by an obligation although he did not receive anything (Siftei Cohen 40:7).

The Rambam distinguishes between this and the previous law as follows: In the previous instance, although the person did not owe the recipient anything, when he undertook the obligation his commitment was limited and specific; therefore, it became binding. In this instance, since the commitment is not specific, we cannot know that the giver made a serious and binding commitment. It is possible that he was speaking facetiously and never desired to give the full amount that he promised.
The Ra’avad, the Ramban and the Rashba differ with the Rambam, and maintain that even in such an instance, it is possible to make a binding commitment. The Shulchan Aruch (Choshen Mishpat 60:2 and 207:21) states the Rambam’s opinion on this issue and concludes: “And all the later scholars differed with him, and we follow their ruling.”

Even if the husband limits the time-frame of the commitment, it still resembles the law stated in the previous halachah.

As the Rambam states in Hilchot Zechiyah UMatanah 6:17 and Hilchot Ishut 23:17, when a man makes commitments to his wife at the time he consecrates her, they are binding, even though he did no more than make a verbal commitment. Although ordinarily such commitments would have to be supported by an actual kinyan, because of the great love the man feels at the time he consecrates his wife he makes a binding commitment through a verbal statement alone.
The commitment mentioned in this halachah is being made at the time of marriage, not of consecration. Therefore, a verbal commitment is not sufficient, and a kinyan is necessary. Nevertheless, because of the love felt at the time, the kinyan made on this occasion is binding even with regard to a commitment that ordinarily would not need to be upheld.

According to the law stated in Halachah 15.

As stated in Halachah 7.

In this way, even if the commitment the person made is an asmachta, he is bound by virtue of his original commitment.

Engagements are a classic example of asmachtot, for no one expects to break an engagement. Hence, any commitments made in the event that the engagement is broken - e.g., the man will pay the woman several thousand dollars - are asmachtot.

More precisely, the translation of this verb is “abuse.” We have chosen this translation with regard to business transactions, because as the Rambam states in this halachah, the prohibition against ona’ah applies even when a person unknowingly takes unfair advantage of a colleague. Thus, even when he is not consciously abusing his colleague, he is nevertheless transgressing. The understanding of the prohibition against ona’ah within the context of verbal abuse is developed in the latter part of Chapter 14.

Sefer HaMitzvot (Negative Commandment 250) and Sefer HaChinuch (Mitzvah 337) consider this to be one of the 613 mitzvot of the Torah.

By paying the amount that was over- [or under-] charged, or by nullifying the transaction, the person corrects the transgression. Since neither a transgression that can be corrected, nor a transgression that involves a financial penalty, is punishable by lashes, that punishment is not administered in this instance.

As the Rambam states in the following halachah, if the profit is less than one sixth of the value of the article, there is no requirement to return the money. Nevertheless, it is not sufficient to return an amount that will reduce the profit margin below one sixth; the entire profit must be returned.

The Maggid Mishneh objects to the Rambam’s ruling, explaining that although the margin of profit is less than one sixth when compared to the article’s value, it is more than one sixth when compared to the price the purchaser paid. Moreover, the unjust gain in this situation is a greater percentage of the article’s worth than if an article worth 60 were sold at 70.
Therefore, the Maggid Mishneh suggests the following principle: As long as the margin of gain is within a sixth, either from the standpoint of the seller or from that of the purchaser, we say that the ona’ah will be waived. On this basis, he maintains that the Rambam’s wording should be emended and changed to read “an article worth 70 dinarim for 60 and a p’rutah.” The Shulchan Aruch (Choshen Mishpat 227:3) quotes the example given by the Maggid Mishneh.
The Ramah (Choshen Mishpat 227:4) differs with the Maggid Mishneh’s premise and maintains that ona’ah is determined always with regard to the value of the object sold and not the amount of money the person paid. For it is in the appreciation of the article’s value that an error can be made.

The Rambam’s wording leads to the inference that taking any amount of unfair gain is forbidden. Nevertheless, since a person is wont to waive this amount in business transactions, the person who took the unfair gain is not required to return it. Note, however, Hilchot Geneivah 7:5, which states that as long as a coin is worth 5/6 of its value, it is permitted to use it for a business transaction, for people are wont to forgo up to a sixth of the value.
The Tur (Choshen Mishpat 227) states:
Since the Torah states: “Do not take unfair gain,”... if the seller or the purchaser is aware that he is taking unfair gain... it is forbidden.... Or perhaps since it is an ordinary business practice [to mark up one’s merchandise],... this is therefore not called ona’ah at all.
See also the Shulehan Arueh (loc. cit.:6).

The Maggid Mishneh draws attention to Chapter 27, Halachah 5, which states that if it is plainly obvious that there is unfair gain involved - e.g., a person sold an article for double its worth - the laws of ona’ah do not apply. Instead, we assume that the purchaser was giving the seller a present.

The Tur (loc. cit.) and Sefer Me’irat Einayim 227:6 emphasize that the purchaser may not demand: “Let the purchase stand; just return the unfair gain to me.” Instead, he must either keep the merchandise at the price he paid, or return it to the seller.

The rationale is that since he was the one who wronged his colleague, he is not given any prerogative with regard to the nullification of the transaction. The Tur and the Ramah (Choshen Mishpat 227:4) differ and maintain that since the transaction is not binding, even the one who wronged his colleague can bring about its nullification. (See also Halachah 13 and notes.)

It would appear that according to the Rambam, as long as the unfair gain exceeds a p’rutah, it must be returned. The Rambam’s opinion [quoted by the Shulehan Arueh (Choshen Mishpat 227:5)] is thus an intermediate view between two opinions quoted by the Tur: one (also cited by the Ramah), which requires even a p’rutah of unfair gain to be returned, and another (cited by Sefer Me’irat Einayim 227:12), which maintains that unless the ona’ah is a m’ah, the smallest silver coin, it is not considered of consequence and need not be returned.
[Sefer Me’irat Einayim also maintains that the Rambam subscribes to the view he explains. Significantly, it is advanced by Rabbenu Yitzchak: Alfasi, the teacher of the Ri Migash, the Rambam’s own teacher.]

Kiryat Sefer distinguishes between robbery, where a p’rutah must be returned, and the law at hand as follows. In robbery, the person did not receive anything. In this instance, a transaction was involved, and he received something for his money or property. Hence, since the unfair gain was only a p’rutah, it is not of consequence.

Perhaps we should have used the word “opportunity.” For as the Shulchan Aruch (Choshen Mishpat 227:7) writes, if he is prevented from appraising the article by forces beyond his control, he has the right to protest afterwards.

Who can honestly appraise the article for him.

I.e., a relative knowledgeable in this field.

Although the Rambam is obviously pointing to an exaggerated difference in value, based on Chapter 27, Halachah 5, his wording in this halachah is not precise.

Since he did not take the opportunity to inquire whether or not his transaction was worth the price he paid for it, we assume that he desired it and was willing to purchase it at any cost. Thus, he forfeits his right to protest.

When the unfair gain is an even sixth.

When the unfair gain is more than a sixth.

Since there is no way we can guarantee that he will see a similar article in a given time, he is always given the opportunity to retract.

For he will always be able to see if he received a fair price or not.

The halachic principle governing this and the previous rulings is that once a person has waived a particular right, he cannot reclaim it.

One might think that since a merchant is knowledgeable with regard to prices, that he was aware of the true value of the article. Thus, if he purchased it or sold it for considerably more or less than its value, he was giving a present to the other party. The Rambam states that this is not the case and that there is also the possibility that he will err.

Sefer Me’irat Einayim 227:26 explains that since the Torah mentions ona’ah with regard to a sale, one might think that these laws do not apply with regard to the exchange of coins, for such a transaction is not regarded as a sale. Therefore, the Rambam emphasizes that the laws do apply.

I.e., according to the Rambam, the measure of one sixth applies with regard to the exchange of coins as well. The Maggid Mishneh, the Tur and the Ramah (Choshen Mishpat 227:15) differ and maintain that with regard to coins the measure of ona’ah is one twelfth. When there is any greater gain, the transaction is nullified. If there is a lesser gain, it is allowed to stand without change.
Sefer Me’irat Einayim explains that a smaller figure is mentioned with regard to coins, because people are very careful with regard to their value and expect to be given a fair exchange.

At that time, the value of coins was determined by their weight, not by their face value. If a coin was the approximate size, but not the proper weight, the laws of ona’ah applied.

If, however, the sela’im are being exchanged by weight, the transaction would be nullified in such an instance, as reflected in Chapter 15 [Maggid Mishneh; Shulchan Aruch (Choshen Mishpat 227:16)].

In Halachot 5-7, a standard amount of time was allocated in which the worth of an article was to be evaluated, or else the person is considered to have waived his right to protest. A similar concept applies with regard to coins. The determination of that amount of time is the subject of this halachah.

For villagers often come to the cities before the end of the week to purchase their Sabbath needs, and on that trip they could have the coin evaluated.

The Rambam was speaking before the age of the printing press, when books (more precisely, scrolls) were extremely valuable articles, whose worth could be appraised only by experts.

Since there was no way that the purchaser could have the article appraised, the passage of time is of no consequence.

As the one that was given.

The Maggid Mishneh interprets the Rambam’s words as meaning that even if a person who received a coin of improper weight did not return it in the time allotted in the previous halachah, he may still return it at a later time if it will not be accepted as currency. If it will be accepted, even with difficulty, the person who gave it is not obligated to take it back.
The rationale for the Rambam’s ruling is that if the person cannot use the coin he received, this is not merely a case of taking unfair profit, but rather of giving an article with a defect.

I.e., the time mentioned in the previous halachah.

The Rambam’s ruling is based on his understanding of Bava Metzia 52b. The Tur and the Shulchan Aruch (Choshen Mishpat 227:17) offer a different interpretation, explaining that even if the coin is not acceptable as currency, the one who gave it is not obligated to accept it after the time period mentioned in the previous halachah.

Halachah 4.

Even the opinions mentioned by the Ramah (Choshen Mishpat 227:4) that ordinarily allow the seller to retract do not give him that option in this situation.

An unfair gain sufficient to nullify the transaction.

As stated in Halachot 1 and 2.
Thus, in addition to the profit the purchaser gains from the increase in the value of the object, he also gains another zuz from the seller.

I.e., in addition to the loss he suffered because of the article’s decrease in value, he must pay another zuz from his pocket.