1) A NEARLY PERFECT LOAF
QUESTION: In the Mishnah (80b), Rebbi Yehoshua states that the loaf of bread used for an Eruv must be whole. In the Gemara, Rebbi Yochanan ben Shaul adds that the loaf of bread may be missing "Kedei Chalasah" or "Kedei Dimu'ah" and still be used for an Eruv.
We know that the smallest amount that may be separated as Chalah is 1/48th of the total amount of dough. The amount of Terumah in a mixture that gives the mixture the status of Dimu'a is 1/100th of the total. If a piece the size of 1/48th of the loaf may be missing from the loaf, why does Rebbi Yochanan ben Shaul add that it may be missing even a piece that is 1/100th of the loaf? 1/100th is much smaller than 1/48th!
ANSWERS:
(a) RASHI explains that the Gemara is not referring to a loaf that is missing a piece which is either 1/48th or 1/100th of the loaf. Rather, the Gemara means that the loaf is missing that amount because one had to remove it for the sake of a Mitzvah (either to fulfill the Mitzvah of Chalah, or to remove the Dimu'a). Since that part was separated from the loaf in order to make the bread fit to be eaten, the bread is not considered lacking.
Why, then, does the Gemara say that one may remove "Kedei Chalasah" ("the size of its Chalah") if it refers to separating the actual Chalah itself? The Gemara should say "Chalasah" alone, and not "Kedei Chalasah"!
TOSFOS (DH Kedei) explains that by adding the extra word "Kedei Chalasah," the Gemara is teaching that when one separates more Chalah than necessary, the loaf of bread may not be used for the Eruv, because the inferior loaf will cause ill feelings among the other neighbors who contributed to the Eruv. When one separates only the minimum amount of Chalah, the others realize that the bread is lacking only because Chalah was taken from it and they will not be upset.
(b) The ROSH and RITVA challenge this explanation. How do the other residents know the reason why a piece of bread was cut off from the loaf? They do not know whether it is missing because Chalah was taken from it or because it is a broken, inferior bread.
The Rosh and Ritva explain instead that regardless of why the bread is missing a piece, it may be used for an Eruv as long as the missing piece is only "Kedei Chalasah" or "Kedei Dimu'ah." "Kedei Chalasah" means 1/48th of the bread. "Kedei Dimu'ah" also refers to an amount that is approximately 1/48th of the bread. "Dimu'ah" here does not refer to the amount of Terumah that forbids Chulin, but to the amount of Terumah that one must separate from his produce in the first place (as in the verse, "Mele'ascha v'Dim'acha," which refers to Terumah). The normal amount of Terumah that is separated from produce is 1/50th, which is very close to the amount of Chalah separated from dough (1/48th). The Gemara is merely expressing the same measure with two examples, and it does not mean that Chalah or Terumah was actually taken from the loaf. The Gemara's point is that when such a small amount is missing from the bread of the Eruv, it does not cause discord among the neighbors.
HALACHAH: The SHULCHAN ARUCH (OC 366:6) rules like the ROSH that a loaf missing 1/48th is a valid Eruv, even if that amount was not separated for the sake of a Mitzvah.
Does this ruling apply to Lechem Mishneh on Shabbos? We know that we must use two complete loaves at each of the Shabbos meals. How much may be missing from a loaf for the loaf to remain valid for Lechem Mishneh?
The KORBAN NESANEL (7:12:3) writes that the ruling of the Rosh applies only to bread used for an Eruv. Bread used for Lechem Mishneh on Shabbos is considered whole only when the part it is missing is due to a Tikun, some corrective act, that was done to it; that is, it is considered whole only when it is lacking due to the removal of Chalah from it (like Rashi here says).
However, the SHA'AREI TESHUVAH (OC 274:1) cites the HAR HA'KARMEL (#2) who rules that even if the piece was broken off in order to separate Chalah from the bread, it is not considered a whole loaf with regard to Lechem Mishneh.
2) GIVING MONEY TO A BAKER IN ORDER TO BE INCLUDED IN THE ERUV
QUESTIONS: In the Mishnah, Rebbi Eliezer and the Chachamim argue about a case in which one gives money to a baker so that the baker will give a loaf of bread on his behalf to the Eruv. The Chachamim maintain that the person who gives the money to the baker is not included in the Eruv. The buyer expects his money to acquire for him a loaf of bread, but since "Ein Ma'os Konos" (the transfer of money does not effect an acquisition) he does not acquire the bread through the act of giving money alone. Rebbi Eliezer maintains that the Eruv works for that person because "Ma'os Konos" and he successfully acquired the loaf of bread which the baker gave to the Eruv on his behalf.
RASHI (DH Lo Zachu) explains that according to the Chachamim, since the baker received money from the person on behalf of the bread, when the baker is Mezakeh bread to everyone in the Chatzer he does not have intention to be Mezakeh a portion to the person who gave him money. Rather, he has intention to sell the bread to him, but the sale is not valid because "Ein Ma'os Konos." Consequently, the person does not have a share in the Eruv.
The Mishnah says that the reason why the person does not acquire a share in the Eruv by giving money to the baker is because "Ein Me'arvin l'Adam Ela mi'Da'ato," an Eruv cannot be made for someone without his consent. What does this case have to do with his consent? The reason he is not included in the Eruv is because "Ein Ma'os Konos"!
Rashi seems to address this question (DH Lo Zachu). He explains that "he did not have intention [to be Koneh]." Rashi apparently means that the man who gave the money to the baker did not want the baker to give him a gift of a loaf of bread. Rather, he wanted to purchase the loaf with his money. Since his money cannot be Koneh it for him, the loaf is not his. Even if the baker is Mezakeh to him a loaf, he will not be Koneh because he has "refused" to receive it as a gift by giving money to purchase the loaf. (Rashi repeats this more clearly on 81b, DH she'Ein.) This is what the Mishnah means when it says that one cannot make the loaf become a person's Eruv against his will.
However, why does Rashi first suggest another reason for why the person was not Koneh the loaf? Rashi says that the baker did not intend to be Mezakeh a portion of the loaf to the person who paid for the Eruv, since he thought the man had already purchased his portion. This reasoning is not necessary! Even if the baker intended to give the buyer an additional, free loaf of bread, the buyer should not be Koneh it since he "refused" to accept any other bread without payment! (TOSFOS, ROSH)
ANSWER: The PIRYO B'ITO discusses the comments of Rashi at great length (he calls them the most difficult comments of Rashi in the Maseches) and summarizes the various forced answers suggested by the Acharonim. Perhaps we may understand the words of Rashi based on our earlier observation of the style of Rashi in Eruvin, as follows.
We have seen elsewhere in Eruvin that Rashi's words occasionally appear to be a combination of two different versions of his commentary (see Insights to Eruvin 51:2 and 65:3, and see Rashi to 43a, DH Halachah). (In the text of Rashi that appears in our edition of the Gemara, the first version of Rashi's commentary and the second version are combined, with no break between them to denote that they are two completely different explanations. The apparent inconsistency in the words of Rashi in these places prompts the MAHARSHAL to erase part of Rashi's comments in some of these places.)
The commentary of Rashi here appears to be another such occurrence. Apparently, Rashi understood the Sugya at two different times in two different ways. The words "d'Keivan d'Ma'os" begin the second explanation of Rashi.
The second explanation of Rashi is consistent with the way TOSFOS (DH Lo) and the other Rishonim explain the Gemara, and it is the way Rashi himself explains later (81b, DH she'Ein). This appears to be Rashi's revised and preferred explanation. According to this approach, when a person gives money to buy a portion of the Eruv, he has implicit intent that he does not want someone to be Mezakeh to him his portion in the Eruv, but he wants to purchase it with money. Consequently, since he thinks that he has acquired the bread because he paid for it, he does not acquire it when the baker attempts to be Mezakeh it to him, because he does not consent to accept it as a gift. This is also the intent of the Mishnah when it says, "she'Ein Me'arvin l'Adam Ela mi'Da'ato" -- since the person does not intend to acquire a portion in the bread as a gift, the Eruv cannot be made for him (as he also does not acquire it with money, because "Ein Ma'os Konos").
Rashi learned the Gemara differently in his first explanation. It is not the intent of the purchaser (to buy the bread and not receive it as a gift) that prevents him from joining the Eruv. Rather, it is the baker's mistake that prevents the buyer from joining the Eruv. The baker mistakenly assumes that the person who gave him money for the bread is already included in the Eruv because he bought a portion, and therefore the baker does not have intention to be Mezakeh it to him as a gift.
In what way, though, is this related to the principle of "Ein Me'arvin l'Adam Ela mi'Da'ato"? The answer is that when the Mishnah says "she'Ein Me'arvin...," it is teaching an entirely new and unrelated law. It is as if the Mishnah says, "v'Ein Me'arvin" and not "she'Ein Me'arvin." (We find that the letter "Shin" in the Mishnah is interchangeable with a "Vav" -- see Eruvin 44b and the marginal note on the Mishnah and Tosfos Yom Tov there, based on Beitzah 8a). These words are unrelated to the previous statement in the Mishnah, according to Rashi's first explanation of the Sugya. (See ROSH 7:13 who explains the Mishnah in this way as well.)

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