The Mishnah (1:10) lists three cases that related to dofen akuma. This rule allows for up to four amot of invalid schach adjacent to a wall. The wall is consider curved and in direct contact with the valid schach. This principle is not derived from logic; rather it is a halacha le’moshe mi’sinai.
Let us ask a basic question: how does dofen akuma work? Rashi (Sukka 17a) brings two understandings. The first is that we view the pasul schach as part of the wall and that the wall is bending at the top, meeting the kosher schach. The second understanding, which Rashi rejects, is that we view the wall itself as if it is bending underneath the invalid schach and touching the valid schach. Rashi dislikes this second understanding because the Mishnah rules that if there is only three tefachim of air space between the walls and schach then the sukkah is invalid. According to the second understanding we should have simply been able to rely on dofen akuma and view the wall as if it was bending and touching the schach.
The Gemara earlier (4a) discusses another case that also ultimately relies on dofen akuma.We started the masechet by learning that the maximum height of a sukkah is twenty amot. The Gemara discusses the case of a three-walled sukkah that is taller than twenty amot and teaches that one can build a platform, thereby raising the floor of the sukkah to within twenty amot of the schach. This is true even the platform is adjacent to only two of the walls, provided that it is within four amot of the third since we can rely on the dofen akuma. The question there is how does dofen akuma help?
Once again the two understanding can be applied in this case. The Ran explains that we view the space between the wall and the platform, including the schach above, as the thickness of the wall. However as walls are naturally bent, we consider this “thick” wall to have bends as well. This understanding aligns with Rashi’s first explanation above. The Ran also rejects the second understandings for the same reason as Rashi earlier.
Interestingly, the Ran and Ritva there cite Rashi who explains that we view the wall as if it is bending toward the platform. Such an explanation is one that Rashi rejected earlier. We do not have this explanation of Rashi printed in our Gemara but rather have Rashi explaining in a similar manner cited earlier, that aligns with the Ran.
Even though our text of Rashi does not present this contradiction it is nonetheless worth addressing. The reason is that the Rambam appears to provide a different explanation in our case and the case of the platform. In our case he explains (Sukkah 5:14): “…we consider the wall to be bent and the pasul schach to be part of the wall.” This aligns with the first explanation. In the case of the platform, the Rambam explains (Sukkah 14:14): “…it is as if the walls are touching the platform...” The Maggid Mishnah understands that the Rambam here is consistent with the second understanding – the wall is consider bending in.
Rav Soleleitchik (Harerei Kedem 102) answers that there are two dinim in dofen akuma. In the case of the platform, bending the wall at the top would not help as it the wall is still too far from the platform. The schach itself is fine, albeit too high from the ground. It is bringing the wall closer to the platform helps. In our case however we cannot bring the wall closer to the kosher schach as there is pasul schach that prevents it from doing so. The issue however is resolved if the pasul schach becomes considered part of the wall. The Rav notes both methods cannot be applied at the same time. For example if there was also pasul schach in the space between the platform and third wall, the sukkah would be pasul.
The Kesef Mishnah finds it difficult to suggest that the Rambam understands that dofen akuma acts differently in the different cases. Instead he suggests that we have misunderstood the Rambam in the case of the platform. Instead the Rambam holds the same position as the Ran that the walls are considered as if they are touching the platform in combination with the schach in that space.
The Aruch Hashulchan (632:3) resolves the apparent contradiction by combining both explanations. The first step in the halacha of dofen akuma is that we consider the pasul schach as if it is part of the wall. He understands that this alone is insufficient as the kosher schach is still at a distance from the (upright) wall. He continues to explain after the first step is achieved, we then view the wall as if it is bending towards the kosher schach. Both steps however are required.
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