Keilim, Chapter 12, Mishnah 5. Throughout this chapter the Mishnah takes up small pieces of metal, many of them components of larger objects, and asks in each case whether the piece carries the status of a utensil on its own. Ordinarily a nail bears no tumah whatsoever: it performs no task by itself and is nothing more than an appendage to whatever it has been hammered into. Our Mishnah therefore turns to the exceptions: nails that their owner reshaped or set aside so that they now do a job independently, and a metal rod that served a moneychanger at his table.
A nail reshaped into a key
The Mishnah begins with a "masmer shehitkino", a nail whose owner bent or filed it "lihyot pote'ach veno'el bo", so that he could unlock and lock a door with it. Such a nail is tamei, that is, capable of receiving tumah. It entered the world as a common nail, but its form was altered to serve a fresh purpose, and through that reworking it became a utensil in its own standing, a key that carries out real work.
A nail used as a marker
"He'asui lishmirah, tahor." If the nail was set up for the sake of watching over a room, it remains tahor. Picture a nail placed in the doorway in a particular position, so that its owner can later check whether it has shifted; if it moved, someone entered the room. That nail is a marker and nothing more. Since it does no active work, it never becomes a keli, and it cannot receive tumah.
A nail designated for opening a barrel
Next comes a "masmer shehitkino", a nail earmarked by its owner "lihyot pote'ach bo et hechavit", to be the implement with which he taps open a wine barrel. On this the Tannaim differ. "Rabbi Akiva metamei": in his opinion the nail is susceptible to tumah, since its owner has appointed it as an instrument that does a job. "Vachachamim metaharin ad sheyitzrefenu": according to the Chachamim it stays tahor until he has tempered it in fire.
Tempering means heating the metal until it is very hot and then plunging it swiftly into water. The metal hardens and the tool becomes considerably stronger. The Chachamim reason that before the nail has been treated this way it is not really fit for the job, because it is liable to crack the barrel. A thing that cannot yet do its work is not yet a keli, and only the tempering brings it to that stage.
Rabbi Akiva disagrees. In his view the nail can already be used to open the barrel al yedei hadechak, with difficulty, even before it has been hardened. Since the job is possible, the owner's designation by itself is enough to transform the nail into a keli that is susceptible to tumah.
The money changer's bar
The Mishnah now moves to a metal rod sunk into the wooden pillar that stood before a moneychanger's booth. The booth's opening was sealed by a board that served as its door. When the moneychanger opened for business he would take that board down and rest it horizontally upon the pillar, where it became his counter, and the rod was the support that held the board up. That rod never left the pillar; it stayed in place even once the board had gone back to serving as a door.
"Masmer shel shulchani, tahor." According to the Tanna Kamma such a rod cannot receive tumah. Its whole function is to remain fastened to the pillar, and the pillar in turn is planted in the earth, and nothing joined to the earth is susceptible to tumah.
"Rabbi Tzadok metamei." In Rabbi Tzadok's opinion the rod is susceptible to tumah, since its connection is not truly permanent: now and then the moneychanger pulls it out and employs it for other needs, and that alone suffices, in his view, to prevent it from being counted as part of the ground. The Chachamim answer that such removals occur only seldom, and an object whose normal place is fixed is judged as joined to the earth and consequently remains tahor.
Three cases of Rabbi Tzadok
Disputes between Rabbi Tzadok and the Chachamim appear in various places in these mishnayot without being gathered in one spot, so the Mishnah now lists them together: "sheloshah devarim Rabbi Tzadok metamei vachachamim metaharin." There are three items about which Rabbi Tzadok rules that they are susceptible to tumah while the Chachamim rule that they always remain tahor.
- "Masmer shel shulchani", the moneychanger's rod, the case our Mishnah has just examined.
- "Ve'aron shel garosot", the box belonging to a grinder of beans.
- "Umasmer shel even sha'ot", the pointer of a sundial.
In all three, "Rabbi Tzadok metamei vachachamim metaharin": Rabbi Tzadok considers each of them a keli that can receive tumah, and the Chachamim hold that all of them stay tahor.
The thread running through the entire Mishnah is a single question: when does a piece of metal stop being a part of something else and start being a utensil of its own? Reshaping it into a key achieves that. Designating it to open a barrel achieves it according to Rabbi Akiva, and only after tempering according to the Chachamim. Setting it up merely as a marker does not achieve it at all, and neither does a bar whose place is in a post fixed to the ground.