Eiruvin 4:10-11

Eiruvin 4:10

If a person started out to make an eiruv techumin to the next town and someone turned him back because of inclement weather, he may go to the other town on Shabbos because he started out with the intention to make his Shabbos residence there. Other people in his town who might have relied upon that eiruv may not go to the next town because the eiruv wasn’t actually set. This is the opinion of Rabbi Yehuda; Rabbi Meir says that one who could have placed an eiruv but didn’t is like the “donkey driver/camel driver.” [This metaphor was used previously in mishna 3:4. Because of doubt as to whether or not the eiruv took effect, one is limited to the space from his home to the eiruv’s location. See our parenthetical note on 3:4 for full details.]

Eiruvin 4:11

If a person went outside the Shabbos boundary, even by a single cubit, he may not re-enter on Shabbos. Rabbi Eliezer says that if he overstepped the boundary by two cubits (about three feet) he may re-enter (because his personal four cubits still overlap the boundary) but not if he overstepped by three cubits. If a person is outside the Shabbos boundary even by a single cubit when Shabbos arrives, he may not enter. Rabbi Shimon says that even if one is outside by 15 cubits he may enter because the surveyors are imprecise; they leave this as a margin of error for those who accidentally overstep the boundary.

Editor's note: in the audio shiur, I originally misspoke and said 25 rather than 15. We have since dubbed "15" over "25" and it's (koff koff) barely noticeable.