Section one: This deals with a case where the beam doesn’t fully reach the other side of the entrance, or with a case of two beams, one coming out of each side, that don’t reach other. If there is less than a three handbreadth gap between the beam and the other side or between one beam and the other, the eruv is valid. Rabban Shimon ben Gamaliel says that the gap may be up to four handbreadths.
Section two: This case deals with two thin parallel beams. The beam should be thick enough to hold a half-brick, whose thickness is 1.5 handbreadths. So if the two beams are close enough that they can hold a 1.5 handbreadth wide half brick, they are valid.
Rabban Shimon ben Gamaliel is again more lenient. As long as the two beams can hold the half-brick by its length, which is three handbreadths, they are valid.
Section three: This is the section relevant to our topic. The beams here go all the way across but they are less than one handbreadth wide. If one beam is up top and the other beam is below, the two beams can join together to form the requisite one handbreadth as long as one isn’t above 20 cubits from the ground and the other below ten handbreadths, because these beams must always be below 20 cubits and above ten handbreadths (just like the sukkah).
Rav Ashi now points out the essential issue from this baraita. In section 3 we see that even if the beams are less than one handbreadth wide they can join together, as long as they are all within twenty cubits from the ground. So why then does Rava hold that they must be one handbreadth wide?
Rav Kahana now resolves the baraita. The first thing he does is separate it into three situations. In the first situation both beams are up high, but within twenty cubits from the ground. The lower beam is within three handbreadths of the upper beam, so we can invoke the principle of “lavud”—a gap of less than three handbreadths is considered as if it didn’t exist.
The second situation is almost the same—but both beams are just above ten handbreadths from the ground.
Finally, if the two beams are more than three handbreadths apart, they cannot join by the principle of “beat and throw down” because they are not one handbreadth in width. This resolves the difficulty on Rava.
This section deals with the next clause of the mishnah, which states that if the shade is more than the sun inside the sukkah, the sukkah is valid.
This type of nitpicky question is frequently asked in the Talmud. In my opinion it provides the Talmud with a chance to add a caveat to the Mishnah. In other words, I think the Talmud realizes that the Mishnah doesn’t actually contradict itself. They just posit the contradiction in order to offer a comment about the mishnah.
The mishnah in the second chapter stated that if the shade is greater than the sun the sukkah is valid, implying that if they are equal, the sukkah is invalid. The opposite implication can be drawn from the first chapter. If the sun is greater than the shade, the sukkah is invalid, implying that if they are equal the sukkah is valid. So what is the law if they are equal?
The answer is that it depends on where we measure the shade/sun. If they are equal from above, the sukkah is invalid for down below the sun will appear to dominate the shade (this is according to Rashi). If they are equal below, then above there is more skhakh than empty spaces so the sukkah is valid.
Rav Papa notes a folk-saying that reflects this idea. If there is a hole the size of a zuz, a larger coin above, it becomes smaller below, the size of an issar.
The first part of today’s section contains a baraita related to the last part of the Mishnah. The second part is another mishnah, which will be commented upon and explained on subsequent pages.
Both houses agree that one need not be able to see the stars through the skhakh. While this may surprise some people, the idea that you have to see the stars is not true.
If you can’t even see the sun through the skhakh then it must be really thick. Bet Shammai says that it is invalid. But Bet Hillel doesn’t even invalidate this.
As background to this mishnah we should note that on a festival or Shabbat it is forbidden to climb a tree, lest one break off a branch, which is prohibited on Shabbat and a festival. It is also forbidden to ride on an animal on a festival or Shabbat.
The mishnah uses the language “go up into” the sukkah because sukkot were often built on the flat roofs of their homes. Nevertheless, not all of these mishnayot describe actually going up into a sukkah.
Section one: One can build a sukkah on a wagon or on a ship and one can enter into it on Shabbat. The Talmud explains that the sukkah has to be strong enough to stand up to a wind of common strength. One who builds such a sukkah can enter into on the festival because there is no prohibition of getting onto a ship or a wagon on the festival. Indeed, there is a well-known story in the Talmud of rabbis traveling on Sukkot and making a sukkah on the ship.
Assumedly, Rabbi Judah who in yesterday’s mishnah stated that a sukkah made using a bed’s bedposts is invalid, would also invalidate a sukkah made on a wagon or ship.
Section two: A sukkah made on top of a tree or on the back of a camel is also a valid sukkah (I have actually seen such a thing in Neot Kedumim, near where we live in Israel). However, since it is forbidden to climb a tree or ride on an animal on Shabbat or a festival, these sukkot could only be used during Hol Hamoed, the non-festival days of Sukkot.
Section three: In this and the next section the person doesn’t make his sukkah in a tree but rather he uses a tree to support the roof of his sukkah. A tree can be used to support the sukkah’s wall even though the leaves may not count as skhakh when they are attached to the tree. A sukkah must have at least three walls, so if he uses a tree to support even one these three walls he cannot enter the sukkah on the festival because that would be considered using the tree.
Section four: If, however, he has four walls and only one supported by the tree then the sukkah would be valid and would be able to stand even without the tree. Hence, he may enter this sukkah on the festival because by doing so he is not actually using the tree. The tree-wall is superfluous.
The last clause provides the general rule that sums up what we learned above.