Our sugya starts with a new mishnah.
In this case a person made a sukkah in a cone-shape, somewhat like a teepee. It seems that the upper sections of the walls must have been made of valid skhakh. Alternatively, he leaned a wall made of skhakh against another wall not made of skhakh, somewhat like a lean-to. Rabbi Eliezer rules that this is invalid since a sukkah needs to have a roof. The sages rule that it is valid.
R. Eliezer agrees that the sukkah is valid if he either raises the wall a handbreadth off the ground or distances the leaning wall a handbreadth from the other wall. In both cases a “roof” is formed. In the first case one of the walls is the roof, and in the second he would have to add a little skhakh into the space created in between.
The rabbis of the mishnah allow such a tent-like structure is valid for a sukkah because the incline of a tent, meaning the sides, are treated as if they were the roof of the tent. The sukkah is valid because what looks like the wall can be considered its roof.
In this story Abaye finds R. Joseph sleeping in a bridal bed, one with two posts such that the canopy slopes down on both sides. Evidently, R. Joseph doesn’t think that the sheets that serve as the canopy form a barrier to the sukkah. This is because a tent can’t be a valid sukkah. But, Abaye asks him, this is R. Eliezer’s opinion. Does R. Joseph really hold like R. Eliezer?
R. Joseph defends himself by saying he holds like a baraita in which the opinions from the Mishnah have been reversed. R. Eliezer declares it valid and the sages declare it invalid. So he holds like the sages.
Abaye continues to challenge R. Joseph. How can he rule like a baraita and forsake the Mishnah, usually the more authoritative source?
R. Joseph answers with another baraita. This baraita says the same thing as the Mishnah with one key difference—it is attributed to R. Natan. This allows R. Joseph to deduce that the version of the dispute found in the Mishnah (R. Eliezer invalidates and the sages validate) is only R. Natan’s opinion. Others disagree and R. Joseph rules like them.
We might add in here that it is not uncommon to find sages arguing that what looks like an anonymous opinion is actually disputed, even if we have no explicit source that proves this. It seems that it was important for them to rule like the majority opinion among the tannaim, but that they were willing to be somewhat creative in finding such a source.
Today’s section begins with a new mishnah.
This section of the mishnah requires a few words of introduction concerning the susceptibility of objects to impurity. Objects are susceptible to impurity if they are considered “vessels.” This halakhic category includes most objects that have been fashioned to be of use for people, but not things that are used for building. For instance a cup is susceptible to impurity but a brick is not. In the case under discussion here, a reed mat made to be sat upon is susceptible to impurities whereas a reed mat made to be used as skhakh is not.
According to the sages, all small mats may have been made to be sat upon and hence they are all susceptible to impurity. We learned above in mishnah four that anything that is receptive to impurity cannot be used as skhakh. Hence, small reed mats cannot be used for skhakh. A large reed mat may have been made either to sit upon or to use as skhakh. Hence, its susceptibility to impurity and its validity as skhakh depend upon the intent in which it was made. If it was made to be used for sitting, it cannot be used as skhakh. But if it was made to be used as skhakh then it is valid.
Rabbi Eliezer says that the size of the skhakh does not matter. All that matters is whether the mat was made for sitting or for skhakh. As long as it was made for skhakh it can be used as such, no matter its size.
The Talmud begins by trying to draw out a contradiction within the mishnah. The mishnah says that if he makes it intentionally to recline upon it, then it is subject to impurity and cannot be used as skhakh. However, if he had no specific intention as to its use when he made it, then it is usable as skhakh.
However, the second half says that it usable for skhakh only if he made it with the purpose of using it as covering. If he made it without any express purpose, it would be assumed that he made it for reclining and he wouldn’t be able to use it.
Thus the mishnah contradicts itself in terms of what the law is when a mat is made without it having an express purpose. The first half would say it is valid for skhakh whereas the second half would say it is not.
The Talmud resolves this difficulty by saying that the first half of the mishnah refers to a large mat. Such a mat is valid as use for skhakh even if it was made without any intention as to its use. Since it is large, we can assume that the intent was to use it for a covering.
However, if it is a small mat and it was made without any specific intent, it is invalid, because we can assume it was made to be used for reclining.
In other words, if something is made without any intent in mind, its size will determine its function and susceptibility to impurity.
We should also note how the Talmud “teases” more information out of a mishnah. The mishnah teaches only the simple situations—where he made the mat for an express purpose. It doesn’t really state what the rule is if he had no use in mind when he made the mat. The Talmud gleans this info out of the mishnah by trying to create a contradiction between the first half and the second half. This is a common talmudic technique.
This section continues the analysis of the mishnah from yesterday’s section, again addressing the question of whether the mat can be used as skhakh if it was made without any intention as to how to use it.
The Talmud now applies the same logic it did in yesterday’s section to R. Eliezer’s opinion. In the first half of his words R. Eliezer says that if one made the mat to recline upon is susceptible to impurity. But without any designated purpose, it is not susceptible to impurity.
But in the second half he says the opposite. If he made it specifically for covering, it can be used as skhakh. But if he had no purpose in mind when he made it, then we can assume he was going to use it for reclining and it is invalid as skhakh.
Rava resolves this difficulty and explains the entire mishnah. When it comes to a large mat, which is usually used for covering, both opinions agree that if he makes it with no intent, it can be used as skhakh. No intent implies that it will be used in its normal fashion. They disagree concerning a small mat. The first opinion in the mishnah holds that a small mat is usually made for reclining. Therefore, if he has no intent when he makes it, he cannot use it for skhakh. Rabbi Eliezer disagrees and holds that a small mat is usually made for a covering as well. Therefore it too can be used as skhakh unless it was specifically made to be used for reclining.
 Note that I have translated this section according to the emendation put into the printed edition. Usually, brackets mean that one should read those words and parentheses means one should ignore those words.