1) THE PROOF THAT ERUV CHATZEROS IS MORE LENIENT THAN ERUV TECHUMIN
QUESTION: The Gemara teaches that since the laws of Eruvei Chatzeros are more lenient than the laws of Eruvei Techumin, we might have thought that the principle that the Halachah follows the lenient opinion with regard to Eruvin applies only to Eruvei Chatzeros but not to Eruvei Techumin. The Gemara proves from the Mishnah later (81b) that the laws of Eruvei Chatzeros are more lenient. The Mishnah states that one may make an Eruv Chatzeros for someone else without his knowledge, but one may not make an Eruv Techumin for someone else without his knowledge.
How does this show that the laws of Eruvei Chatzeros are more lenient? The same Mishnah there states that the reason why one may not make an Eruv Techumin for someone else is because it is disadvantageous ("Chov") for him, since the Eruv causes him to lose his Techum of two thousand Amos in the opposite direction. One may make an Eruv Chatzeros for someone else only because it is a benefit ("Zechus") for him, since it gives him the ability to carry from his home into the Chatzer. This reason is unrelated to whether one type of Eruv is more lenient than the other! How, then, does the Gemara prove from here that Eruv Chatzeros is more lenient than Eruv Techumin?
ANSWER: TOSFOS (DH v'Ein) answers that in truth both Eruv Chatzeros and Eruv Techumin involve a slight disadvantage for the person. When one makes an Eruv Techumin for someone else, even if he knows for certain that the other person wants to travel in the direction where the Eruv is being made, he still causes the other person to lose the Techum on the other side. Although this is considered only a slight detriment to him, it is enough to disqualify an Eruv made without his knowledge. When one makes an Eruv Chatzeros for someone else, he takes from the other person a loaf of bread to put in the communal collective (even if he first gives the loaf to his friend, he still takes it from him for the collective, and this is considered a slight "Chov"). Even though his friend gains the Eruv Chatzeros, he still loses his loaf of bread, and this constitutes a slight detriment to the person for whom the Eruv is made. Since both types of Eruv have slight detriments, yet we see that one is permitted to make an Eruv Chatzeros, but not an Eruv Techumin, for someone else without his knowledge, it is evident that the laws of Eruvei Chatzeros are more lenient.
2) "NOT TO FORGET THE CONCEPT OF ERUV"
OPINIONS: The Gemara says that there is a difference between "Shiyurei Eruv" (making an Eruv Chatzeros from food that was already set aside for the Eruv in previous weeks) and "Techilas Eruv" (food set aside for the first time for an Eruv Chatzeros). The Halachah in the case of Shiyurei Eruv is more lenient.
The Gemara cites proof for this premise from the Mishnah later (80b) which states that when one uses an old Eruv, he may use the leftover food even if it is less than the amount of food that is normally required for an Eruv. The Mishnah continues with a cryptic statement: "We make an Eruv only so that the concept of Eruv not be forgotten from the children." What does the end of that Mishnah mean, and how is it connected to the statements that precede it?
(a) RASHI (80b, DH Ela she'Lo) explains that even though a Shituf Mavo'os joins together all of the people in all of the Chatzeros that open into the Mavoy, the people in each Chatzer around the Mavoy must still make an Eruv Chatzeros in order to join the Chatzeros together. Why is that Eruv Chatzeros necessary, if it is already permitted to carry from one Chatzer to another, and to the Mavoy, because of the Shituf Mavo'os? The Mishnah explains that the Eruv Chatzeros is not really necessary in order to permit carrying there, since the Shituf Mavo'os already combines all of the Reshuyos and permits carrying from one to another. Rather, the purpose of making the Eruv Chatzeros is in order to prevent people from forgetting the concept of Eruv Chatzeros, lest people forget to make an Eruv Chatzeros in a place where there is no Shituf Mavo'os. As a safeguard, the Rabanan decreed that an Eruv Chatzeros must be made even when there is no need for it.
Since, in most cases, an Eruv Chatzeros is technically not necessary (because the Shituf Mavo'os is operative), the Rabanan were lenient with regard to "Shiyurei Eruv" and did not require the normal amount of food that is needed for an Eruv.
(b) RASHI here (DH v'Lo Amru) gives a different explanation, with which TOSFOS (DH she'Lo) concurs. The Mishnah does not mean that Eruvei Chatzeros are made "so that they should not be forgotten," but that Shitufei Mavo'os are made for that reason.
That is, in order to permit carrying into a Chatzer and into a Mavoy, an Eruv Chatzeros -- which joins the various Chatzeros around a Mavoy with each other -- should suffice. Why did the Rabanan enact the additional requirement of Shituf Mavo'os? They enacted the requirement of Shituf Mavo'os in order to provide a reminder for the concept of Eruvei Techumin. The Rabanan decreed that a Shituf Mavo'os, which consists of two meals' worth of any type of food, be made in order to remind us of the concept of Eruvei Techumin. (Apparently, Shituf Mavo'os, more than Eruv Chatzeros, is reminiscent of Eruvei Techumin because it can be made with any food like an Eruv Techumin, whereas Eruvei Chatzeros may be made only with bread.)
3) THE DIFFERENCE BETWEEN "HALACHAH," "MATIN," AND "NIR'IN"
OPINIONS: Rebbi Yakov and Rebbi Zereika said that the Halachah follows Rebbi Akiva only when one of his colleagues disputes his ruling. The Halachah follows Rebbi Yosi even when a number of his colleagues dispute his ruling. The Halachah follows Rebbi when one of his colleagues disputes his ruling.
Rav Asi said that these rules are the "Halachah." Rebbi Chiya bar Aba said "Matin." Rebbi Yosi bar'Rebbi Chanina said "Nir'in."
What is the difference between these three expressions of whom the Halachah follows?
(a) According to RASHI, "Halachah" means that the Rav is to teach this rule or opinion in the public lecture. "Matin" means that although it is not taught publicly, the Rav should instruct individuals to follow this opinion when they ask how they should conduct themselves. "Nir'in" means that the Rav should not instruct individuals to follow this opinion, but if an individual conducts himself in accordance with this opinion, the Rav is not to stop him (and we do not revoke the results of what was done in accordance with this opinion).
(b) TOSFOS (DH Rav Asi) explains that all three expressions mean that this opinion is taught publicly. The only difference between them is what is done if a person accidentally follows the other opinion.
"Halachah" means not only is this opinion taught publicly, but if one did not act in accordance with this opinion, then b'Di'eved the consequences of his act are entirely invalid (for example, if the ruling involved the performance of a Mitzvah, one must perform the Mitzvah again). "Matin" means that this opinion is taught publicly, but if one ruled otherwise his ruling is not revoked. Nevertheless, if no one has acted yet in accordance with the erroneous ruling, we do not let them act upon it. "Nir'in" means that although it is taught publicly, we allow one who rules like the other opinion to act upon his ruling.