Rabbah responds by differentiating between the reasoning lying behind his halakhah and the reasoning behind the halakhah of the other rabbis. Rabbah explains that four cubits is the “standard size”—it is the accepted measure of invalid skhakh that invalidates a sukkah. Rabbah knows that this is the measure of invalid skhakh because it is found in the mishnah. If there isn’t this measure, and there is less than four cubits of invalid skhakh next to less than three handbreadths of open air, the sukkah is still valid.
But the other rabbis who say four handbreadths of invalid skhakh invalidates the sukkah hold that the reasoning is that four handbreadths is sufficient to divide the sukkah. Four handbreadths is the minimum measure for something to count as a place unto itself. Therefore, if there is a “place” large enough to divide the sukkah, then the skhakh cannot all be counted as part of one sukkah. If this is so, then why should three handbreadths of invalid skhakh next to two handbreadths of open air, which is valid, be different from four handbreadths of invalid skhakh, which is invalid.
According to Rabbah in yesterday’s section invalid skhakh and open air do not join together to invalidate a sukkah. Abaye, Rabbah’s student, points out that sometimes they do.
In a small sukkah that is seven handbreadths by seven handbreadths, the measure of either invalid skhakh or open air that would disqualify the sukkah would be 3 handbreadths. And in such a case, clearly the open air and invalid skhkakh would join together to invalidate the sukkah. Since they can join together in a small sukkah, Abaye argues against Rabbah that they should indeed join together to invalidate even in a large sukkah.
Rabbah responds that the reason in a small sukkah three handbreadths disqualifies for both open air and invalid skhakh is not because the measures are equal. They just happen to be equal in such a small sukkah. Rather, the reason that they join together in that case is that since three is greater than the measure of “lavud”—the minimum measure to count as significant— it turns out that the remaining valid skhakh, less than four handbreadths, would not sufficient to have a valid sukkah, which needs to be seven handbreadths.
The Talmud continues to object to Rabbah who stated that whenever there are different measures the different items don’t join together to be susceptible to impurity.
This mishnah (Kelim 27:2) teaches that there is a different measure for susceptibility to impurity depending on the material. Cloth (a garment) is the most expensive material and therefore it is susceptible even if it is only three handbreadths squared. Sacking, leather, and matting each have slightly higher minimum measures.
A baraita related to this mishnah teaches that two of these materials can join together. Thus if one has 2 handbreadths of garment sewn together with three handbreadths of leather, the piece is susceptible to impurity, despite the fact that they have separate measures.
The Talmud now explains that the case of the minimum size for a garment is different because in certain situations all of these materials have the same minimum measure. If anyone cuts and evens out a piece of one handbreadth square from any of them, it is susceptible to the impurity conveyed by a zav (a person with unusual genital discharge) who sits on it. In other words, while generally they each have their own distinct minimum measure to be susceptible, in at least one case they are the same. That is why they can join together even in other cases to become large enough to be susceptible.
As an addendum the Talmud asks what one could possibly do with such a small piece of material. The answer is that one could patch up the saddle of a donkey. Thus, if cut properly, even a very small piece of cloth, leather, etc. can have use and be susceptible to impurity.
The above discussion (from section 2 of this daf) was the way that the rabbis in Sura, a center of learning in Babylonia, taught this material. They taught it as a long dialogue between Rabbah and the other rabbis.
In Nehardea, a different center of learning, they taught the same debate but it in a different manner, ascribed to different sages. Rav Judah said in the name of Shmuel that there is a difference between invalid skhakh on the sides and invalid skhakh in the middle. On the sides, it invalidates only if there are four cubits. But if in the middle, it invalidates if there are four handbreadths. This accords with the opinion of the rabbis in the previous discussion.
In contrast, Rav holds that the same measure of four cubits applies in both places. This accords with Rabbah’s opinion above.
The Talmud uses the mishnah to raise a difficulty on Shmuel. The mishnah holds that one plank of four handbreadths does not invalidate the sukkah. This accords with Rav who holds that in the middle of a sukkah, four handbreadths of invalid skhakh does not invalidate the entire sukkah. But Shmuel holds that in the middle of the sukkah four handbreadths does invalidate. Thus the mishnah presents Shmuel with a difficulty.
The difficulty is resolved by saying that the plank was on the side of the sukkah. When placed at the side Shmuel agrees that four handbreadths does not disqualify.
The Talmud now cites another baraita which presents a difficulty to the earlier version of Rav’s opinion (the “Sura” version, the position held by the rabbis of the house of Rav). Rav held that four handbreadths of invalid skhakh invalidates the sukkah if placed in the middle of the sukkah.
We have seen this baraita before (daf 14a). It teaches that according to R. Meir, if one places side by side two boards that are each not the minimum measure to disqualify the sukkah, they join together to disqualify the sukkah.
If Rav holds that four cubits of invalid skhkakh disqualifies the sukkah, then we can make sense of the baraita. The two planks combine together to add up to the four cubits.
But if Rav holds that four handbreadths invalidates in the middle as well (the opinion of the rabbis of the “house of Rav” in the Sura version), then we have trouble understanding this baraita. If each board is four handbreadths itself then it need not combine with another board. Even one such board invalidates the sukkah.
And if the board is less than four handbreadths, then it is not invalid skhakh (Rav holds that all tannaim allow boards less than four handbreadths, see 14a). So how can we understand this baraita.
The Talmud resolves the difficulty by saying that the baraita refers to boards which are each four handbreadths placed on the side of the sukkah. There they do not invalidate the entire sukkah unless together they combine to be four cubits.