Siman - Eruvin Daf 42
- If one does not know where techum ends
Rav Nachman said in the name of Shmuel, היה מהלך ואינו יודע תחום שבת – if someone was walking on Shabbos and he does not know where the Shabbos techum ends, מהלך אלפים פסיעות בינוניות – he may walk two thousand average-sized steps in one direction, וזו היא תחום שבת – and this is the measure of the techum. Rashi explains that the distance traveled by a person with each step is one amah.
- Nochrim encircled one’s makom shevisa with a partitions
Rav Nachman also said in the name of Shmuel, שבת בבעקה והקיפוה נכרים מחיצה בשבת – if he made his Shabbos residence in an open field (thereby giving him two thousand amos from that spot), and nochrim encircled it with partitions on Shabbos, מהלך אלפים אמה – he may still walk only two thousand amos from his makom shevisa. Rashi explains that since the eruv took effect when it was an open area, we cannot consider the large enclosed area as dalet amos based on walls erected later. ומטלטל בכולה על ידי זריקה – However, he may transport objects within the entire enclosure by means of throwing. Since the field is enclosed it has the status of a reshus hayachid in which carrying is permitted.
Rav Huna agrees that he can walk two thousand amos in any direction from his makom shevisa, but he may only be מטלטל ארבע אמות, - carry four amos. He does not permit throwing the object beyond his techum, שמא ימשך אחר חפצו – out of concern that he might be drawn after his object and step out of his techum. He restricts carrying within the two thousand amos of his makom shevisa, משום דהוי כמחיצה שנפרצה במלואה למקום האסור לה – because this case is similar to a partition that was breached along its entire length, leaving it completely open to a place in which carrying is forbidden. Meaning, that since the enclosed area now has two areas, one in which he is permitted to walk and should be permitted to carry in, and another in which he is forbidden to carry in even by throwing, because it is beyond his techum limit, and these two areas are not partitioned off from each other, he is forbidden to carry even within his two thousand amos.
- Two reasons why halacha is like Rabban Gamliel regarding walking on a boat
In the Mishnah on Daf 41b, Rabban Gamliel and Rebbe Eliezer ben Azaryah were in a boat that had sailed beyond the techum, and they walked within the entire ship on Shabbos, whereas Rebbe Yehoshua and Rebbe Akiva did not move out of their four amos.
The Gemara brings two explanations why the halacha is like Rabban Gamliel. Rabbah says, הואיל ושבת באויר מחיצות מבעוד יום – because he established his Shabbos residence within the walls of the ship while it was still day, which enables him to treat the entire ship as his four amah area. Rebbe Zeirah said the reason is, הואיל וספינה נוטלתו מתחילת ארבע ומנחתו בסוף ארבע – because the ship is constantly in motion, he constantly gets a new dalet amos within which to walk. The Gemara addresses what the practical difference is between these two opinions.
