- Two additional explanations of the eruv locked in the closet and the lost key
The Gemara brings two more explanations for the machlokes between the Tanna Kamma and Rebbe Eliezer regarding an eruv locked in a closet and the key is lost.
Rabbah and Rav Yosef both say, הכא במגדל של עץ עסקינן – we are dealing with a closet made of wood. The Tanna Kamma holds that it is a כלי, and אין בנין בכלים ואין סתירה בכלים – and the melachah of building and destroying does not apply to utensils. Therefore, the person may break open the closet even on Shabbos. Rebbe Eliezer holds the closet is an ohel, which may not be demolished on Shabbos or Yom Tov. The eruv is invalid because it is inaccessible.
Abaye and Rava both say, במנעול וקטיר במתנא עסקינן – We are dealing with a closet that has a lock, which is tied with a rope, and a knife is needed to cut the rope. The Tanna Kamma held like Rebbe Yose who said, כל הכלים ניטלין בשבת – All keilim may be taken on Shabbos except for מוקצה מחמת חסרון כיס. Therefore a knife can be used to cut the rope. Rebbe Eliezer holds like Rebbe Nechemyah who holds that keilim can only be taken, לצורך תשמישן – for their primary use. Therefore, the knife cannot be used.
- An eruv becoming inaccessible
The next Mishnah states, נתגלגל חוץ לתחום – If the eruv rolled beyond the techum, ונפל עליו גל, - or a heap of rubble fell on it, if this occurred while it is still day, it is not a valid eruv. If it occurred after dark, it is a valid eruv. The Gemara clarifies that in the first case, the eruv rolled beyond four amos from the edge of the techum, and in the second case, according to Rebbe, it was a case where he needed a hoe and a pick to excavate the eruv, which is the issur d’Oraysa of digging. If it was just a case of moving the muktzeh rocks by hand, it would be permissible to do according to Rebbe during bein hashemashos.
The Gemara explains that both cases are needed. The case of נתגלגל חוץ לתחום teaches that even if a wind could blow it back inside the techum, the eruv is still invalid. The case of נפל עליו גל teaches that even though it is physically within the techum, the eruv is not valid.
- Rebbe Meir goes l’chumroh in a case of a safek eruv
The Mishnah introduces a machlokes when it is a safek when the eruv became inaccessible, with Rebbe Meir going l’chumrah and prohibiting use of the eruv. The Gemara clarifies that Rebbe Meir goes l’chumrah because he holds techumin are a d’Oraysa. The Gemara questions this based on Rebbe Meir saying that one may use the lenient method of מקדרין בהרים for measuring the techum. This method involves viewing a mountain as if it was drilled through, and is only permitted in d’Rabbonan cases. How could Rebbe Meir permit this if he holds techumin are d’Oraysa? The Gemara answers that Rebbe Meir himself holds that techumin are d’Oraysa and he was only quoting his Rebbeim who permitted מדקרין בהרים because they held techumin are a d’Rabbanon.