At the bottom of 18a Rava questions the statement attributed to Rabbi Yohanan that all flaxen garments may be laundered during Hol HaMoed. On the top of 18b Abaye explains, defending the position of Rabbi Yohanan; yet when Bar Hidya offers support to Rabbi Yohanan (- to Abaye) from the practice of people in Tiberia to launder flaxen clothes during Hol HaMoed - Abaye himself rejects the support, saying that perhaps the practice of people in Tiberia was contrary to the wishes of the rabbis.
Two questions:
(a) after all - Rabbi Yohanan was Rabbi in Tiberia! And we have learned that Rabbi Yohanan DOES permit laundering flaxen clothes during Hol HaMoed! Obviously what the people did was in accordance with Rabbi Yohanan!
(b) Why does Abaye reject this support of his position?
Do you think it reasonable to suppose that Abaye was acting here as a teacher, telling Bar Hidya that - although in this case the practice is supportive - in general we cannot prove from common practice what a ruling should be: we must confirm that the practice was accepted by the Rabbis before taking the practice as normative!?
Thank you for this "discussion net"
Yeshayahu HaKohen Hollander
Tosefos [Dibur Hamaschil Maschil] and the Ritva there ask your very question.
The Ritva gives 2 answers. His 1st answer is like yours. In his 2nd answer he says that maybe Abaye holds that even though it is permitted to wash flax in private, nevertheless, it should not be done in public for this could cause one to transgress and do it on Yom Tov as well.
Tosefos says that Abaye forbids kibus of flaxen clothes even though the Mishnah, according to Rav Yochanan, permits it.
Your question regarding the fact that Rabbi Yochanan was the Rav in Tiberias is answered by both answers of the Ritva. According to Tosefos, though, your question remains.
The answer might be that clearly, Abaye would not argue with Rebbi Yochanan. Tosfos must hold that according to Abaye, Rebbi Yochanan never said that it is permitted to wash flax garments on Chol ha'Mo'ed.
-Mordecai