On today’s daf, the rabbis are considering whether a side post that extends from an alleyway into the public domain permits one to carry within the alleyway on Shabbat. The conclusion is that this sort of side post does permit one to carry within the alleyway on Shabbat.
The gemara reports that upon hearing this ruling, Rav Yosef exclaims: “I did not hear this teaching.”
Who was Rav Yosef and why should it matter if he remembers this teaching or not?
Rav Yosef was a leading scholar of the third generation of talmudic rabbis in Babylonia and was known for his ability to remember rabbinic teachings from the time of the Mishnah. He was an active participant in the deliberations in the academy in Pumbedita for decades, earning the respect of both peers and students. According to rabbinic tradition, Rav Yosef eventually became ill and forgot all that he had learned during his career.
Why would the Gemara feel the need to report a memory lapse of a revered sage? Perhaps, so that it could also share how his students responded.
Abaye, a student of Rav Yosef and a leading sage in his own right, informs his teacher that not only did he know this law, but it was he who had taught it in the first place:
Abaye said to him: You yourself told us this halacha, and it was with regard to this that you told it to us. As Rami bar Abba said that Rav Huna said: With regard to a side post that extends along the wall of an alleyway and beyond, in which case it appears from the inside to be a continuation of the wall but due to its narrow width it is clearly visible as a side post from the outside, if that side post is less than four cubits long it is considered to have the legal status of a side post. And one may use the alleyway up to the inner edge of the side post. However, if the side post itself extends four cubits, the alleyway has no side post and it is considered to have the legal status of an alleyway, and it is prohibited to utilize the entire alleyway.
Abaye goes on to remind Rav Yosef of the three laws that he had taught should be derived from this teaching:
Learn from it that in the area between the side posts it is prohibited to carry, as Rav Huna rules that one may use the alleyway only up to the inner edge of the side post. And learn from it that the minimal length of an alleyway is four cubits. And learn from it that a side post that is visible from the outside but appears to be even with the wall of the alleyway from the inside is considered to have the legal status of a side post.
When Rav Yosef has a moment of confusion, his students do not ignore him. Instead, they take the time to bring him into the conversation, to remind him exactly what the law is and give him credit for his contributions to the rabbinic endeavor. And ultimately, they choose to preserve this moment by including it in the Talmud.
Of the many rules that we encounter in Tractate Eruvin, this is one we would do well to remember, and to practice, for a long time.