For the past three pages we have considered what to do if we find tefillin outside of the city on Shabbat. Now we address an even more fundamental question: how can we detect if the items that we have found are valid tefillin?
Well, for starters, they ought to have tefillin knots:
The father of Shmuel bar Rav Yitzchak taught that these are old tefillin: Any that have straps that are permanently tied.
New tefillin have straps that are not tied; everyone agrees that a person does not exert himself.
Shmuel bar Rav Yitzchak’s father reasons that because tefillin knots are difficult to tie, no one would bother making them except for bona fide tefillin — so you can trust that an object you find with these knots is in fact a used and loved pair of tefillin, and you can don it and wear it home.
It is possible, however, to find valid tefillin that are so new they are not yet knotted, in which case the finder has a problem: the unknotted tefillin cannot be worn (because without proper knots they are invalid), the knots cannot be tied (because it is Shabbat), and they cannot be carried instead of worn (again, because it is Shabbat). The Gemara attempts a work-around:
Let him simply tie a bow (which is not prohibited on Shabbat) and place the tefillin on his head and arm in that manner.
This opinion is quickly countered by Rav Hisda who argues that “a bow is invalid for tefillin.” A bow, Rav Hisda maintains, does not replace a knot. But Abaye rejects Rav Hisda’s view, citing Rabbi Yehuda who said that actually “a bow is a full-fledged knot.”
Unfortunately, whichever opinion we accept, this doesn’t solve our problem. Either a bow is not a knot, so the tefillin are unwearable (and therefore cannot be rescued because they cannot be carried on Shabbat), or a bow is a proper knot that cannot be tied on Shabbat. In either case, tying a bow will not allow us to rescue unknotted tefillin.
But wait a minute, you ask: isn’t it about the text inside the tefillin? Is a knot really such an integral part of the tefillin? Rav Yehuda, son of Rav Shmuel bar Sheilat, said in the name of Rav:
The form of the permanent knot of tefillin is a halakhah transmitted to Moses from Sinai.
You don’t want to mess with ritual law that is sourced from Sinai to Moses. So yes, you really do need those valid knots.
By the way, if you want to learn how to tie tefillin knots properly, Rabbi Dan Rosenberg has a lovely series of video tutorials on Youtube. You can view them all at his channel.
And, sorry, today’s daf never tells us how to rescue those unknotted tefillin — one should stay with them to protect them until Shabbat ends. So please don’t leave brand new tefillin lying around outside your city on Shabbat.
Read all of Eruvin 97 on Sefaria.
This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on November 14th, 2020. If you are interested in receiving the newsletter, sign up here.