Siman - Eruvin Daf 51
- The source for two thousand amos of a techum
The Gemara seeks the source that a techum measures two thousand amos and brings a Baraisa with the passuk that states, אל יצא איש ממקומו – let no man leave his place, אלו אלפים אמה – this refers to the two thousand amah limit of the techum.
The Gemara asks how it is known that the passuk is alluding to a distance of two thousand amos, and Rav Chisda answers by bringing five gezeirah shavos that link makom from the passuk ultimately to the word chutz in the passuk regarding the open area that surrounds the ערי לויים, ומדתם מחוץ לעיר את פאת קדמה אלפים באמה – And you shall measure from outside the city on the east side, two thousand amos.
- כדי שיהיה נשכר לזוויות
In the Mishnah on 49b, Rebbe Chanina ben Antignos said the two thousand amos are עגולות, they form a circular area and the Chochomim said, מרובעות כטבלא מרובעת, they form a square, like a square board, four thousand amos on each side, כדי שיהיה נשכר לזוויות, - so that he may gain the corners. This means that the person can travel the diagonal of a square which is 1.4 times its side.
The Gemara brings a Baraisa that teaches according to Chochomim, that all measurements for Shabbos observers shall be like the square shape around the ערי לויים. Based on this, Rav Acha bar Yaakov said, המעביר ארבע אמות ברשות הרבים – One who transfers an object a distance of four amos in the reshus harabim, אינו חייב עד שמעביר הן ואלכסונן – is not liable unless he transfers it a distance equal to them and their diagonal, which means he is not liable unless he transfers it 5.6 amos, the diagonal of a four-amah square.
- עיקר עירוב בפת או ברגל
The Mishnah on 49b stated, העני מערב ברגליו – a poor man, meaning a traveler with no food, may make an eruv with his feet, meaning with his physical presence. Rebbe Meir said, אנו אין לנו עלא עני – This law is only for a poor man. Rebbe Yehudah said it applies to both a poor man or a rich man, meaning someone who has food at home, לא אמרו מערבין בפת אלא להקל על עשיר, - The Chochomim did not say for one to make an eruv with food except to make it easier for the rich man, שלא יצא ויערב ברגליו – so that he should not need to go out before Shabbos begins and make an eruv with his feet, meaning with his physical presence.
On our Daf, Rav Nachman and Rav Chisda dispute what the machlokes between Rebbe Meir and Rebbe Yehudah is about.
