The Gemara in Tractate Shabbat, on a page dedicated by Benjamin, begins its discussion approximately four lines from the bottom. The Gemara previously established a universally accepted rule: a source of ritual impurity (tumah) measuring three by three fingerbreadths (shalosh al-shalosh etzba'ot) imparts impurity to wool and flax. This was a point of unanimous agreement. Now, the Gemara proceeds to discuss specific rules of ritual purity and impurity (tumah v'taharah) that are subject to dispute (makhloket).
The Gemara states that there is a practical difference (nafkah mina) between the Tannaim regarding garments made of other materials (she'ar begadim) when they measure three by three handbreadths (tefahim). The question is whether such garments are susceptible to impurity (mikabel tum'ah) or not. The dispute, as the Gemara explains, involves Rabbi Shimon ben Elazar. He would clearly hold that she'ar begadim are susceptible to impurity at this size. After all, when Rabbi Shimon made his original statement, he implied the existence of the law of three by three tefahim, and he would not maintain that it is not susceptible to impurity at all. The Gemara then asks for the source (makor) of this susceptibility to impurity for she'ar begadim.
The Gemara explains that the Torah, when discussing a creeping creature (shiretz) falling on a garment, uses the phrase "or a garment" (o-beged). From the inclusion of "or," it implies that the law refers not only to wool and flax but also to she'ar begadim. As a general rule, whenever the word "garment" (beged) is used in the Torah without further specification, it refers to wool and flax, as is the case with the laws of leprosy (tum'at tzara'at), where the measure is three by three etzba'ot. So the Gemara asks: how do we know that she'ar begadim are susceptible to impurity when they measure three by three tefahim? The Gemara then clarifies the sources: the Torah does not explicitly state this. Rava comes along and says that if a garment measures three by three tefahim, it will be susceptible to the impurity of a shiretz.
Abaye, however, contends that according to everyone, the only garments that receive impurity are wool and flax alone, and there is no impurity of three by three tefahim for she'ar begadim. What then does Abaye do with the phrase "o-beged" that we just learned regarding the impurity of a shiretz? Abaye explains that "o-beged" comes to include that which we did not already know. We know that wool and flax are susceptible to impurity from leprosy (nega'im). But how do we know they are susceptible to impurity from creeping creatures (shiratzim)? The word "o-beged" comes to include even a three by three tefahim garment, specifically of wool and flax, which is also susceptible to impurity from shiratzim.
The Gemara then asks Rava: if "o-beged" teaches us about she'ar begadim, how does he know that flax and wool are susceptible to impurity at three by three tefahim? Rava responds that an extra word is not needed for that. The Merciful One (Rahamana) revealed regarding leprosy (nega'im) that a three by three tefahim garment is susceptible to impurity, and this can be extended to shiratzim (v'hu'adin le-shiratzim) through a principle called Binyan Av. Since the word "beged" is used regarding tum'at nega'im, and we know that "beged" there refers to wool and flax, and it is established that wool and flax are susceptible to impurity at three by three tefahim in tum'at nega'im, then by Binyan Av, whenever "beged" is mentioned regarding tum'at shiratzim, it implies that all garments, specifically wool and flax, are susceptible to impurity at three by three tefahim. This is a Binyan Av from tum'at nega'im.
Abaye, however, rejects this. He argues that one cannot derive the laws of tum'at shiratzim from tum'at nega'im. He states, "Ika le-mefrah, ma le-Nigayim, she-ken, she-ti ve-erev me-tameh behem" – meaning, there is a flaw in this comparison. Leprosy (nega'im) has a stringency (chumrah) in that even the warp and weft threads (she'ti ve-erev) are susceptible to impurity by tum'at tzara'at, a stringency not found in tum'at shiratzim. Therefore, one cannot learn the law of three by three tefahim for wool and flax from a Binyan Av from nega'im to shiratzim, because nega'im is more strict (mahmir).
The Gemara then asks Rava how he would respond to this. Rava argues that if nega'im were indeed more stringent, then why would the Torah need to write "o-beged" by shiratzim to teach this law? It could have simply written this law only by tum'at shiratzim and not mentioned it by tum'at nega'im. We would then learn the law for nega'im from shiratzim through a logical inference (kal v'chomer): if tum'at shiratzim has this impurity, certainly tum'at nega'im, being more stringent, would have it. The fact that the Torah did not do this teaches us that tum'at nega'im is not more stringent than tum'at shiratzim, and therefore, one can indeed learn it from a Binyan Av from nega'im. Thus, three by three tefahim of wool and flax would be susceptible to impurity, and the phrase "o-beged" by tum'at shiratzim would then be available to include she'ar begadim.
Abaye responds that one would never be able to learn nega'im from shiratzim. Rava's claim was that if the Torah had only mentioned shiratzim, we would automatically learn nega'im from it due to its greater stringency. Abaye counters that this kal v'chomer would be flawed (ika le-mefrah). Tum'at shiratzim has its own stringency: it imparts impurity even at the size of a lentil (adasha), whereas tum'at nega'im only imparts impurity at a larger size, called a "gris" (approximately nine lentils). Thus, each has its own unique stringency. Therefore, one cannot learn one from the other, and the Torah had to write an inclusion (ribui) in both cases to teach the law of three by three tefahim. According to Abaye, the "o-beged" by tum'at shiratzim teaches that tum'at shiratzim applies to three by three tefahim, and a separate inclusion is needed for tum'at nega'im. Therefore, Abaye concludes there is no source for she'ar begadim to be susceptible to impurity.
The Gemara then presents another statement by Abaye. Abaye says that we learned from a Tanna from the Beit Midrash of Rabbi Yishmael that the only garments that receive impurity are wool and flax; the general term "beged" in the Torah refers to wool and flax. Abaye explains that this Tanna from the Beit Midrash of Rabbi Yishmael is actually arguing with another Tanna from the same Beit Midrash. So, according to Abaye, there are two Tannaim from the Beit Midrash of Rabbi Yishmael who are at odds. The dispute arises from the phrase "beged" in tum'at shiratzim. While "beged" generally refers to wool and flax, the phrase "o-beged" comes to include other materials like camel hair (tzemer gemalim), rabbit hair (tzemer arnavim), goat hair (notzal sh'rizim), and various types of silk (shirim, kalach, sidikim). These other begadim are also susceptible to tum'at shiratzim. This implies that there is tum'at shiratzim for she'ar begadim, contradicting the first Tanna of Rabbi Yishmael who said only wool and flax are susceptible.
Rava, however, says there is no dispute between the two Rabbis of the Beit Midrash of Rabbi Yishmael. He argues that the first Tanna, who stated there is no impurity for she'ar begadim, was referring only to three by three etzba'ot. However, regarding three by three tefahim, he agrees that she'ar begadim are susceptible. The second Rabbi Yishmael also agrees with this. Therefore, the Torah's mention of tum'at tzara'at with three by three etzba'ot does not minimize the susceptibility of she'ar begadim at three by three tefahim. While there might be a difference between tzara'at and shiratzim regarding three by three etzba'ot, both Rabbis agree that three by three tefahim of she'ar begadim are susceptible to impurity. Thus, according to Rava, the two Tannaim of Rabbi Yishmael are not at odds.
The Gemara then challenges Rava: "What do you mean, Rava? You yourself just told us on the previous page that the dispute between Rabbi Shimon ben Elazar and the Tanna of the Beit Midrash of Rabbi Yishmael was precisely about whether she'ar begadim are susceptible to impurity at three by three tefahim!" How can Rava now say that everyone agrees that three by three tefahim of she'ar begadim are susceptible to tum'at sherezt? The Gemara answers, "Hadar b'Rava me-hachi" – Rava must have retracted his original statement. Therefore, Rava now holds that there is no dispute between the two Tannaim of the Beit Midrash of Rabbi Yishmael, nor between Rabbi Shimon ben Elazar and the Tanna of Rabbi Yishmael. This means, contrary to Abaye's initial assertion, Rava holds that there is no impurity of three by three etzba'ot for she'ar begadim, but there is for three by three tefahim. Thus, Rava's first answer here is that there is no dispute, as both agree that there is tum'ah for she'ar begadim at three by three tefahim. The Gemara reiterates that Rava initially said there was no tum'ah, but he has now retracted that statement.
The Gemara offers another answer: "V'iba'it eima ha-Rav Papa amara" – perhaps this statement, which was attributed to Rava to reconcile the two statements of Rabbi Yishmael, was not actually said by Rava. Instead, it was Rav Papa who made this statement. This resolves the contradiction with Rava's earlier position. Rav Papa explained the first Tanna's statement as follows: when the first Tanna learned the word "beged," he referred to "o-beged" written by tzara'at as a Binyan Av, meaning that any time the Torah uses the word "beged," it refers to wool and flax. However, he was not discussing tum'at shiratzim. Instead, he was referring to the laws of mixed fabrics (kilayim) and specifically to the law of shatnez. The "beged" by tum'at tzara'at, which is wool and flax, comes to teach us that the "beged" mentioned in the laws of shatnez also refers to this specific mixture. Therefore, the first Tanna was not discussing tum'at shiratzim at all. Thus, when the second Rabbi Yishmael comes along and says that tum'at shiratzim applies to other begadim due to "o-beged," the first Rabbi Yishmael can agree. There is no contradiction between them.
The Gemara challenges Rav Papa's explanation: "Do you need a Binyan Av to tell me that shatnez applies specifically to wool and flax? We already know that! It is explicitly written: 'You shall not wear shatnez, wool and flax together' (lo tilbash shatnez tzemer u'fishtim yaḥdav)." The Gemara answers that one might have thought that the prohibition of "lo tilbash" (you shall not wear) only applies when one is actually wearing the garment. However, "ha'ala'ah" (placing it over one's shoulder) might apply to any fabric. The verse "u'beged kilayim shatnez lo ya'aleh alecha" (a garment of mixed materials, shatnez, shall not come upon you) uses the term "ya'aleh," which is not necessarily "wearing." Therefore, the Binyan Av from tzara'at is needed to teach us that even for ha'ala'ah, the prohibition of shatnez applies only to wool and flax.
The Gemara again challenges this: "Is that not a kal v'chomer?" If wearing (levisha), which provides more benefit (hana'ah) to the entire body, is only prohibited for wool and flax, then surely ha'ala'ah, which provides less benefit, would also be restricted to wool and flax. It is impossible to think that ha'ala'ah applies to all garments while levisha only applies to wool and flax. Therefore, the Gemara concludes, "Ela, de-Rav Papa baduta hi" – Rav Papa's explanation of the first Tanna is incorrect. Thus, we cannot reconcile the two statements of Rabbi Yishmael based on Rav Papa's explanation.
The Gemara then brings another interpretation to explain the first Tanna of the Beit Midrash of Rabbi Yishmael. This Tanna learned from the word "beged" in tum'at nega'im that it refers only to wool and flax. His statement, "af kol tzemer u'fishtim," was not referring to tum'at shiratzim. Instead, it was coming to teach the law of fringes (tzitzit). Just as the "beged" in tzara'at refers to wool and flax, so too, the garments that are obligated in tzitzit are only wool and flax. Therefore, the first Rabbi Yishmael was never discussing tum'at shiratzim at all. When the second Rabbi Yishmael states that tum'at shiratzim applies to other begadim due to "o-beged," the first Rabbi Yishmael can agree. He meant his Binyan Av to apply only to tzitzit, limiting the obligation to wool and flax. There is no dispute.
The Gemara challenges this: "Tzitzit be-hed ya'ktiv!" – Tzitzit is explicitly written in the Torah! What does it say? "Lo tilbash shatnez tzemer u'fishtim yaḥdav," and immediately after that verse, it says, "Gedilim ta'aseh lach" (you shall make fringes for yourself). From the proximity (semichut) of these two verses, we learn that just as shatnez refers to wool and flax, so too, the obligation of tzitzit applies only to wool and flax. Therefore, we do not need a Binyan Av from nega'im to learn this; we know it from the semichut to shatnez.
The Gemara responds that one still needs this Binyan Av. If one did not have the first Tanna of the Beit Midrash of Rabbi Yishmael to teach that the obligation of tzitzit applies specifically to wool and flax, one might have understood those verses differently. Rava once brought a contradiction between verses regarding tzitzit. One verse states, "Min kanfei bigdeihem" (from the corners of their garments), which implies that the material of the tzitzit must match the material of the garment (min kanav). If the corner is silk, the tzitzit must be silk. But another verse states, "tzemer u'fishtim yaḥdav," implying that wool and flax strings can be used for any garment. How are these reconciled? Rava reconciled them by saying: "Tzemer u'fishtim potrim ben mi-minam ben she-lo mi-minam" – wool and flax strings are universally valid; they fulfill the obligation for any type of garment. However, for other materials (she'ar minim), like silk, "be-minam potrim" – they only fulfill the obligation for a garment made of the same material. So, Rava holds that all garments are obligated in tzitzit, but wool and flax strings are universally valid, while other materials require matching strings.
Now, returning to the Tanna's explanation: the Tanna holds that "Min kanav" means that all garments are obligated in tzitzit. But the first Tanna of the Beit Midrash of Rabbi Yishmael says, "No, don't learn 'kanav' like Rava. We learn from tzara'at that the only garments obligated in tzitzit are wool and flax." This was said by Rav Nachman bar Yitzchak. According to the first Tanna of the Beit Midrash of Rabbi Yishmael, he saw a verse in tum'at nega'im that mentioned "beged," and he knew that "beged" there referred only to wool and flax. He then made a general statement that whenever "beged" is mentioned in the Torah, it refers only to wool and flax, specifically concerning tzitzit. But regarding tum'at shiratzim, where an "o-beged" is mentioned, it can include she'ar begadim. So there is no dispute.
The Gemara asks: "Fine, for the same reason that you include she'ar begadim for tum'at shiratzim because it says 'o-beged,' why didn't the Tanna of the Beit Midrash of Rabbi Yishmael, according to Rav Nachman, include she'ar begadim for tzitzit?" The Gemara answers that the verse for tzitzit, "asher tichaseha" (that you cover yourself with), is not extra (yiter) and therefore not available to include she'ar begadim. It is used to include the wool or flax garment of a blind person (soma) as being obligated in tzitzit. The Gemara explains: "U'ritem oto" (you shall see it) implies that the obligation of tzitzit applies only if one can see the tzitzit. This excludes a garment worn exclusively at night (kisut layla), which is exempt from tzitzit. One might think it also excludes the garment of a blind person, who cannot see. However, the verse "asher tichaseha" is an inclusion (ribui) for the garment of a blind person. Thus, "u'ritem oto" excludes kisut layla.
The Gemara then asks: "You have one verse that includes and one that excludes. Why did you choose to include the garment of a blind person and exclude kisut layla? You could have done the opposite!" The Gemara responds: "Marbeh ani kisut soma" – I include the garment of a blind person because there is no contradiction between his garment and the phrase "u'ritem oto." Why? "She-yeshna bi-riyah etzel acherim" – because others can see his tzitzit. However, with kisut layla, nobody can see the tzitzit, not the person wearing it, nor others. Therefore, kisut layla is clearly exempt, and the garment of a blind person is obligated.
So, our question on Rav Nachman's explanation was: you are telling me that the Binyan Av from nega'im teaches that tzitzit applies only to wool and flax. But regarding tum'at shiratzim, she'ar begadim are included because of "o-beged." Why isn't the verse "asher tichaseha" for tzitzit also used to include she'ar begadim? The Gemara answers that this verse is used to include the garment of a blind person. But why only the blind person's garment and not she'ar begadim? The Gemara explains that the verse "asher tichaseha" is written next to the verse that mentions "tzemer u'fishtim." Therefore, "asher tichaseha" is an inclusion for more things within wool and flax, specifically the garment of a blind person. It is not reasonable to say that the Torah, after mentioning wool and flax, would then include other garments from "asher tichaseha." It is more reasonable to include more people within the context of wool and flax. So, the Tanna's statement stands: the Binyan Av limits tzitzit to wool and flax.
In conclusion, the Gemara states that Rabbi Shimon ben Elazar's initial statement was that anything susceptible to tum'at nega'im cannot be used for the covering of a Sukkah (sakhach) because it is susceptible to impurity, even if it is not susceptible to tum'at shiratzim. For example, a she'ti ve-erev (warp and weft threads), which is not susceptible to tum'at shiratzim but is susceptible to tum'at nega'im, cannot be used for sakhach. The Gemara finds support for this from Rabbi Shimon ben Elazar's statement: "Anything that comes from a tree can be used for sakhach, except for flax (pishtan)." The fact that he did not say "except for a flax garment (beged pishtan)" implies that even unspun flax threads are prohibited. Regular unspun flax is not susceptible to tum'at shiratzim, but it is susceptible to tum'at tzara'at. This is the distinction.
Similarly, Sumchus stated that if one made sakhach with flax strings, it is invalid, not because of tum'at shiratzim, but because of tum'at nega'im. This follows the opinion in the Mishnah that she'ti ve-erev, once it has two strings, immediately becomes susceptible to tum'at nega'im. This is the opinion of Rabbi Meir. Rabbi Yehuda, however, says that it becomes susceptible to impurity when it is removed from the cauldron where it is whitened. The bundles of flax (unim) become susceptible when placed in the oven for whitening. Thus, according to Rabbi Yehuda, even bundles of flax that have not yet been spun are susceptible to tum'at nega'im. This aligns with Abaye's interpretation that these items, though not susceptible to tum'at shiratzim, are still invalid for sakhach due to their susceptibility to tum'at nega'im. As Sumchus said, following Rabbi Meir, it becomes susceptible immediately. Or, as Abaye said, following Rabbi Yehuda, even unim (bundles) of flax are susceptible to tum'at nega'im, rendering them invalid for sakhach. Baruch Adonai. Amen, amen, amen.