Keilim, Chapter 27, Mishnah 11. This chapter is occupied with cloth and fabric and the minimum measurements by which they are able to receive tumah. Our mishnah takes up a related question: beyond size, what condition must a piece of cloth still be in for it to count as a usable article at all? And does it make a difference whether that cloth is sitting in a person's house or lying in a garbage dump?
Three by three tefachim in the ashpah
The mishnah opens: "Sheloshah al sheloshah ba'ashpot, bari vesored melach." A piece of cloth measuring three tefachim by three tefachim that was discarded into a garbage dump can become tamei only if it possesses two qualities together. First, it must be bari, whole and sound, without a tear in it. Second, it must be sored melach, still sturdy enough that salt could be wrapped up in it.
The logic is straightforward. If the cloth is still capable of holding salt inside it, it retains a use, and therefore it retains the standing of a keli that can receive tumah. Once it can no longer do even that, it has no use left whatsoever, and it forfeits its status as a keli. For a cloth that its owner has thrown away, both conditions are required together.
The same cloth in the house
The next clause turns to that very same cloth when it is sitting "babayit", indoors, having never been thrown out. Here the mishnah presents the two qualities as alternatives rather than as a pair: "o bari" or "o sored melach". It is enough that the cloth be free of tears, and it is equally enough that it be firm enough to hold salt; either quality on its own leaves it able to become tamei.
How much salt?
Now the mishnah fixes the amount: "Kama melach yehe sored?" Its answer is "Rova", a fourth of a kav, a volume that comes out to six beitzim, six eggs.
Here a machloket enters, not about the amount but about the kind of salt in which we measure it. "Rabbi Yehudah omer, badakah. Vachachamim omrim, bagasah." Rabbi Yehudah holds that we test the cloth with a rova of fine salt, while the Chachamim hold that we test it with a rova of coarse salt.
The mishnah then makes a remarkable comment: "Elu va'elu mitkavnim lehakeil": each of the two opinions is aiming at leniency. Rabbi Yehudah is persuaded that his standard is the lighter one, and the Chachamim are just as persuaded that theirs is. Neither side is arguing for stringency; the entire dispute is over which measurement actually comes out leniently.
Why each Tanna considers himself lenient
Rabbi Yehudah, who requires that the cloth be able to hold fine salt, reasons that fine salt is the harder test. Fine salt is denser, since there is less empty space between the grains, and so a rova of fine salt is heavier than a rova of coarse salt. The cloth must be able to bear that greater weight. On his view this is a leniency: if the cloth cannot support the heavier load, even though the volume is the same rova in either case, it does not become tamei at all.
The Chachamim reverse the calculation. To their mind, a cloth meant to hold coarse salt has to be more durable than one meant for the fine variety, since large grains have jagged points that pierce and rip fabric. It follows, in their view, that tumah takes hold only in a cloth robust enough to contain coarse salt, and they consider that the more lenient standard.
So each Tanna is convinced that he holds the lighter position, and the argument between them is only about which standard is in fact more demanding of the cloth.
Rabbi Shimon: the discarded cloth drops a level
Rabbi Shimon dissents. "Rabbi Shimon omer", he declares the two cases "shavim", equivalent: a cloth of "sheloshah al sheloshah ba'ashpot", three tefachim by three tefachim in the garbage dump, falls under the identical ruling as a cloth of "shalosh al shalosh babayit", three etzba'ot by three etzba'ot inside the house.
Just as a cloth of three fingerbreadths by three fingerbreadths cannot receive tumat midras even inside the house, because it is simply too small, so too a cloth cast into the garbage cannot receive tumat midras even when it does have the full minimum measurement and even when it is whole and strong enough to hold salt. In Rabbi Shimon's understanding, the very act of discarding it brings it down a level, and from that point it can no longer become tamei with tumat midras, whatever its size and condition.