The previous discussion in the Talmud Bavli, Masechet Sukkah, explored a significant disagreement regarding the minimum number of walls required for a sukkah. The Tanna Kamma stated that two conventional, solid walls are necessary, with the third wall needing only to be a handbreadth wide. In contrast, Rabbi Shimon held that three conventional walls are required, and the fourth wall can be a handbreadth. The current discussion focuses on the placement of this minimal third or fourth handbreadth-wide wall.
The Gemara asks: "Where is that handbreadth placed?" Rav responded that it should be positioned at the end of one of the existing, protruding walls. This means if two walls are perpendicular, the additional handbreadth is placed along the end of one of them, extending in a straight line. Rashi clarifies that this placement can be on any desired side. For instance, if the two perpendicular walls are east and north, the handbreadth can be placed at the end of the northern wall, extending west, or at the end of the eastern wall, extending south.
Rav Kahana and Rav Assi then questioned Rav, suggesting an alternative: "Why not place it diagonally, like a 'head of an ox'?" This configuration, known as a rosh tor, involves placing the handbreadth diagonally at a corner. Rashi explains that this diagonal placement, for example, in the northwest corner, makes it appear as if two walls are created, thereby resembling four walls in total, as it touches two different directions. The term rosh tor refers to the diagonal furrow at the end of a field, which resembles this pointed, slanting shape. Rav remained silent, indicating he had no immediate answer to this suggestion.
It was also stated that Shmuel, in the name of Levi, agreed with Rav, maintaining that the handbreadth should be placed straight, "at the end of the protruding wall." This was also the ruling in the study hall. However, Rabbi Simon, or some say Rabbi Yehoshua ben Levi, offered a different opinion. He suggested using a "generous handbreadth" (a tefach sochek), which is slightly wider than a standard handbreadth (measured with fingers slightly apart). This generous handbreadth should be placed less than three handbreadths away from an existing wall. By applying the halachic principle of lavud, which considers gaps of less than three handbreadths as closed, this arrangement effectively creates a wall of four handbreadths. The significance of four handbreadths is that it constitutes a majority of the seven-handbreadth minimum length required for a sukkah wall, ensuring a valid wall according to this view.
Next, the Gemara considers a sukkah constructed like an alleyway (a mavoi), where the two main walls are parallel rather than perpendicular. Rav Yehuda stated that such a sukkah is valid, and the third handbreadth-wide wall can be placed on any of the four open sides. Rashi explains that even parallel walls are considered "conventional walls" in this context, and with four open ends, the third wall can be positioned as desired.
Rabbi Simon, or some say Rabbi Yehoshua ben Levi, offered a different approach for a sukkah configured like an alleyway. He required a plank (a pas) that is four handbreadths wide plus a little extra, placed less than three handbreadths from a wall. Again, applying the principle of lavud, this creates a wall of seven handbreadths. The Gemara immediately questions the discrepancy: "Why did he say a generous handbreadth is sufficient for perpendicular walls, but here he requires a four-handbreadth plank?" The Gemara answers that with perpendicular walls, there are already two fully conventional walls. Therefore, the third wall can be less substantial. However, with parallel walls, which are not considered two fully conventional walls because they do not meet, the third wall must be more significant, hence the need for a four-handbreadth plank to achieve a seven-handbreadth wall when combined with the lavud principle.
Rava then introduced a novel concept: for perpendicular walls, the third wall is only valid if it is constructed as a "doorway form" (a tzurat hapetach). This involves two vertical posts with a crossbeam on top, similar to an entrance. Rashi clarifies that this means the handbreadth mentioned earlier must be formed by two vertical posts, each half a handbreadth wide, placed at the ends of the existing walls, with a crossbeam connecting them. This structure is considered a sealed wall in halacha. There are two interpretations of Rava's statement: some say it is an alternative to the generous handbreadth, meaning one can choose either method. In this interpretation, the vertical posts of the tzurat hapetach can be very thin. Others say Rava means that the tzurat hapetach is required in addition to the generous handbreadth. Rav Ashi observed Rav Kahana constructing a sukkah using both the generous handbreadth and a tzurat hapetach, and when asked, Rav Kahana confirmed he followed the stricter interpretation requiring both.
The Gemara then shifts to apply the laws of sukkah to the laws of Shabbat. The Tanna Kamma's opinion that a sukkah requires two conventional walls and a third wall of merely a handbreadth is revisited. Rabbah stated that this rule also applies to Shabbat. This means that if a sukkah is built in a public domain (a reshut harabim) with two conventional walls and a handbreadth-wide third wall, it is considered a private domain (a reshut hayachid) on Shabbat Sukkot. Therefore, one is permitted to carry items between their house and such a sukkah. This is based on the principle of migo: "since it is considered a wall for sukkah, it is also considered a wall for Shabbat." Rashi explains that while normally three conventional walls are needed to create a reshut hayachid on Shabbat, on Shabbat Sukkot, the special dispensation for the sukkah's wall applies to Shabbat laws as well, due to the migo principle, which stems from a tradition given to Moses at Sinai.
Abaye challenged this migo principle, citing a teaching: "A sukkah wall is like a Shabbat wall, provided that the gap between reeds is not three handbreadths." This refers to walls made of vertical posts (a sheti) or horizontal ropes (an erev), where gaps of less than three handbreadths are closed by lavud. The teaching continues: "But Shabbat has an advantage over sukkah: Shabbat is only valid with more standing material than open space, which is not the case for sukkah." This implies that for Shabbat, the walls must be mostly solid, whereas for sukkah, even if there is more open space than solid material (e.g., due to many doorways in the walls), it can still be valid. Abaye argued that this "advantage" of Shabbat (meaning a stricter requirement) must refer to Shabbat Sukkot in a sukkah. If so, it would mean that even if a sukkah is valid for dwelling with more open space than solid wall, it would not be valid for carrying on Shabbat, thus contradicting the migo principle that a sukkah wall is always a Shabbat wall.
The Gemara refutes Abaye's interpretation. It clarifies that the statement "Shabbat has an advantage" means that a regular Shabbat is stricter than Shabbat Sukkot. On a regular Shabbat, a structure with more open space than solid wall is not a valid reshut hayachid. However, on Shabbat Sukkot, the migo principle applies: since the structure is a valid sukkah wall, it is also a valid Shabbat wall for carrying, even with more open space. The Gemara then asks why, if this is the case, the teaching doesn't also state the reverse: "Sukkah (on a weekday) is stricter than sukkah on Shabbat." This would imply that for a regular sukkah, a generous handbreadth is needed as a third wall, but for a sukkah on Shabbat, a mere beam (a lechi), which is less than a handbreadth, would suffice, because a lechi is considered a wall for Shabbat laws (e.g., in an alleyway). This would mean that the migo principle would work in both directions: if it's a wall for Shabbat, it's a wall for sukkah, and vice-versa. The Gemara answers that this is obvious, as Shabbat is generally more stringent than sukkah. If a lenient rule (sukkah's handbreadth wall) can apply to a stringent area (Shabbat's carrying laws), then a stringent rule (Shabbat's lechi wall) can certainly apply to a lenient area (sukkah's wall requirements).
Rava then stated two cases where the migo principle applies. First, if one places sukkah roofing (sechach) over an alleyway (a mavoi) that has a lechi, the sukkah is valid. Since the lechi makes the alleyway a valid reshut hayachid for Shabbat, it is also considered a valid wall for the sukkah. Second, if one places sechach over the "well-partitions" (passei bira'ot), the sukkah is valid. Passei bira'ot are four L-shaped corner structures, each one cubit long, placed around a well in a public domain. These are considered walls for Shabbat out of leniency for pilgrims needing water. The Gemara asks why all three cases (sukkah with more open space than solid wall, sukkah over an alleyway with a lechi, and sukkah over passei bira'ot) are necessary to teach the migo principle. It explains that each case highlights a unique aspect. The alleyway case has two conventional walls, making the lechi's validity for sukkah understandable. The passei bira'ot case lacks two conventional walls but has the "name of four walls" due to the L-shapes, making its validity for sukkah a novel teaching. Finally, the case of more open space than solid wall is necessary to show that the migo principle works even from a lenient sukkah rule to a stringent Shabbat rule. Thus, all three cases are needed to demonstrate that the migo principle applies universally, between Shabbat and sukkah laws in both directions.
The Mishnah stated that a sukkah with more sun than shade is invalid. The Rabbis taught that this refers to sun from the sechach, not from the walls. This means if the sechach provides sufficient shade, the sukkah is valid, even if the walls allow much sunlight. Rabbi Yoshiyah, however, held that the "more shade than sun" requirement applies to the walls as well. Rav Yeimar bar Shelamya, in the name of Abaye, explained Rabbi Yoshiyah's reasoning: a verse states, "You shall cover the ark with the curtain (parochet)." Although the parochet was a partition (a wall), the Torah uses the term "cover" (v'sakkota), implying it functions like sechach. Therefore, just as sechach must provide shade, so too must the walls. Some scholars infer that Rabbi Yoshiyah would only permit walls made of materials suitable for sechach. The Rabbis, in contrast, interpret the verse "You shall cover the ark" as merely instructing to slightly bend the parochet to resemble a roof, not that the wall itself is considered sechach.
Abaye then asserted that Rabbi, Rabbi Yoshiyah, Rabbi Yehuda, Rabbi Shimon, Rabban Gamliel, Beit Shammai, Rabbi Eliezer, and "others" (often identified as Rabbi Meir) all share the fundamental principle that a sukkah must be a permanent dwelling (a dirat keva). The Gemara proceeds to demonstrate this for each authority:
- Rabbi: He stated that any sukkah smaller than four by four cubits is invalid. This size is considered the minimum for a permanent dwelling, like a house.
- Rabbi Yoshiyah: As discussed, he required walls to provide shade like sechach, indicating a preference for a house-like, protected dwelling.
- Rabbi Yehuda: He validated a sukkah taller than twenty cubits, while the Tanna Kamma invalidated it. The Tanna Kamma held that a sukkah must be a temporary dwelling (a dirat arai), and a structure over twenty cubits is inherently permanent. Rabbi Yehuda's validation implies he seeks a permanent dwelling.
- Rabbi Shimon: He required three conventional walls and a fourth of a handbreadth. This increased wall requirement, based on a verse about protection from rain, suggests a more substantial, permanent structure akin to a house.
- Rabban Gamliel: He invalidated a sukkah built on a wagon or a boat. Rashi explains that these are temporary or unstable structures, not fitting the definition of a permanent dwelling.
- Beit Shammai: They invalidated a sukkah where one's head and most of one's body were in the sukkah, but the table was in the house. Rashi explains that a sukkah must be fit for permanent use, including having a table inside, like a house.
- Rabbi Eliezer: He invalidated a sukkah shaped like a hut (a tzrif), where the roof and walls are one continuous slope, or one leaned against a wall. He considered these invalid because they lack a distinct roof and do not resemble a proper dwelling.
- Acherim (Rabbi Meir): They invalidated a sukkah built like a dovecote (a shovach), which is circular, because it lacks corners. A normal house has corners, and the absence of them makes it unsuitable as a permanent dwelling.
Tosafot notes that while all these Rabbis agree that a sukkah must be a dirat keva, they differ on the specific criteria for what constitutes a permanent dwelling. For example, Rabbi required four by four cubits, while Beit Shammai considered a sukkah large enough to fit one's head, most of one's body, and a table as sufficient, indicating different standards for "permanence."