“Can I get credit for that?” It’s a question you might have asked as a student or posed to your accountant during tax season. While we often do things intentionally, sometimes we seek credit for them only retroactively. This is the crux of the conversation on today’s daf.
Yesterday, we encountered a mishnah which taught that one could construct a conditional eruv. Basically, you set up two eruvim in two different locations before Shabbat, and then on Shabbat itself you can decide which of those two you wish to use. Today, the rabbis consider whether this principle of retroactive designation applies in all cases. Do you need to determine at the time you undertake an action the particular mitzvah it is intended to fulfill? Or can you decide after the fact?
The daf plays out various scenarios in which one might want to do this. Can you consume some wine that was not tithed and then decide later that the part left over counts for the tithing? What if two birds were brought to a priest for two types of sacrifices, but it wasn’t specified at the outset which bird was for which? In the latter case, one might imagine that if an animal is giving its life for a specific purpose, that would need to be specified at the outset. But the Talmud records the opinion of Rabbi Yosei, who was a bit flexible in this case and allowed the Temple priest to decide which bird should be used for which purpose.
Eventually we get back to our favorite topic, that of the eruv, with this teaching.
If a person were to declare, “I am hereby establishing an eruv for the Shabbatot of the entire year, so that if I want to make use of it, I will be able to walk 2,000 cubits from the eruv, and if I do not want to do so, I will not walk.” If he wanted to make use of the eruv for a particular Shabbat while it was still day, his eruv is a valid eruv for that Shabbat. However, if he only decided after nightfall that he wanted the eruv to be in effect, the tanna’im disagree: Rabbi Shimon says: His eruv is a valid eruv; and the rabbis say: His eruv is not a valid eruv.
In this case, someone wants to establish a permanent eruv and then decide on each particular Shabbat if they wish to make use of it. If the person made the designation during the day, there’s no dispute the eruv is a valid one. But if he waits until later to decide, the rabbis disagree. And there the matter rests, with no broad agreement about whether the retroactive principle can be universally applied.
It’s in the nature of rabbinic discussion to leave certain questions unanswered, which helps explain why we see so many ways of practicing Judaism today. Nonetheless, the Gemara concludes that whichever position you do adopt on this question, you need to stick with it. As we’ve seen already in Tractate Eruvin, consistency is a requirement.
Rav Yosef holds that one who accepts the principle of retroactive designation accepts it in all cases; there is no difference between Torah law and rabbinic decrees. And one who does not accept the principle of retroactive designation does not accept it at all; there is no difference between Torah law and rabbinic decrees.
Sometimes it seems that the rabbis of the Talmud lack flexibility in their interpretation of Jewish law, while other times the laws are quite malleable. But this call for consistency instills a sense of confidence in the overarching Jewish legal system.
Read all of Eruvin 37 on Sefaria.
This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on September 15, 2020. If you are interested in receiving the newsletter, sign up here.