Keilim, Chapter 12, Mishnah 2. This mishnah teaches one governing principle and then applies it to a whole series of everyday objects. The principle is this: when a metal hook is attached to a wooden object, we do not judge the hook on its own. We ask instead what the essential part of the keli is. If that essential part is susceptible to tumah, the hook that serves it is drawn in and becomes susceptible as well. If the essential part cannot receive tumah, the hook attached to it also remains tahor. All the cases in the mishnah are metal hooks fastened to objects of wood, and each one is decided by asking which part carries the identity of the utensil.
The rod of a comber's balance
The opening case involves a portable weighing device belonging to a soreik, a craftsman who combs raw fibers to prepare them for spinning. Picture a lengthy beam of wood with a ring fixed a little way in from one of its ends. That ring is the point from which the beam hangs, so it divides the beam unevenly: one stretch is brief, the other reaches far out. Metal hooks set on the brief stretch, close to the ring, held the fibers being weighed, while a counterweight rode along the extended stretch. The worker shifted that counterweight outward or inward until the beam settled horizontally instead of dipping down. A heavier bundle of fibers pushed the counterweight further from the ring, and the spot where it came to rest told the worker how much the fibers weighed. Words alone make this awkward to picture; a sketch conveys it at once.
The mishnah rules: "Keneh moznayim shel sorakot tamei mipnei ha'unkeliyot," the beam of a comber's balance is susceptible to tumah on account of its hooks. In this scale the metal hooks that hold the fibers are the heart of the instrument. A wooden object with no receptacle is not susceptible to tumah, so the rod by itself would have remained tahor. But since the metal hooks are susceptible, and they are what make this rod into a working scale, the assembled instrument as a whole can become tamei.
The householder's balance
"Veshel ba'alei batim tehorah," the beam of a balance used by householders in the home is tahor. Such a scale had no metal hooks at all. The item being weighed was tied to the beam with a cord, and cord is not susceptible to tumah, so nothing in the instrument draws in the wooden rod. "Im yesh bo unkeliyot, tamei," but if this beam did happen to have hooks fitted to it, it becomes susceptible to tumah exactly like the comber's balance.
The porter's pole and the peddler's pole
Two varieties of carrying pole come next. The katif was a porter, and he worked with a very long wooden pole fitted with a hook at either extremity. His bundles hung from those hooks while the pole lay across both of his shoulders, one load riding ahead of him and the second trailing behind. The rocheil was a traveling merchant who brought his goods from town to town. His pole balanced on a single shoulder, and it too had a hook at each extremity, except that his hooks were shaped as containers, so his merchandise was placed inside them rather than suspended from them.
"Unkelin shel katafin tehorah": a porter's pole keeps its hooks tahor. Here the wood is the dominant element, and a wooden pole that encloses nothing lies outside the reach of tumah. The hooks are no more than accessories to it, so they remain tahor as well. It is worth marking exactly where this case diverges from the comber's scale. There the metal hooks did the work; they were what converted a plain beam into a weighing instrument, so the metal set the ruling and susceptibility spread through the entire device. Here the reverse holds: the pole is the utensil and the hooks are additions to it, so the wood sets the ruling and nothing becomes susceptible.
"Veshel rochlin teme'ah," but the hooks on a peddler's pole are susceptible to tumah. These hooks are genuine receptacles, and they are treated as the principal part of the utensil, so the wooden pole joined to them becomes susceptible on their account. And because a receptacle is susceptible in its own right, without needing to borrow an identity from anything else, the peddler's hook can receive tumah even after it has been detached from the pole.
Rabbi Yehudah on the peddler's pole
Rabbi Yehudah is unwilling to treat the merchant's two hooks alike. "Rabbi Yehudah omer, shel rochlin, shel lefanav teme'ah, shel achorav tehorah." The forward hook, he holds, is susceptible, since that is where the merchant loaded his goods. The rear hook stays tahor, because nothing was ever stored in it. It existed purely as a counterweight, so that the load ahead would not drag the pole off his shoulder. Serving no purpose beyond steadying what hung in front, it never becomes a working part liable to tumah. On Rabbi Yehudah's reading, then, susceptibility on the merchant's pole belongs to the front hook alone.
Six further cases of hooks on wooden objects
Six further illustrations follow, all of them metal hooks fixed to wooden articles in which the wood carries the identity of the utensil while the hook is merely ancillary. Each case has to be weighed separately to determine the outcome regarding tumah and taharah.
"Unkeli dargash teme'ah": a dargash and its hooks alike are susceptible to tumah. The dargash was a couch built from a wooden frame with a leather sleeping surface. Straps extended out of that leather, and a hook at the end of each strap secured it to the frame. Because the couch itself falls under tumah, so do the hooks fastened to it. One may wonder how the wooden frame becomes susceptible when it contains no beit kibul, no cavity for holding anything. The answer lies in its function: it is built to be reclined upon, and whatever is made for reclining or sitting falls under tum'at midras, the tumah transmitted by a person who lies or sits on it. Midras attaches to a keli whether or not it holds anything. The dargash is therefore susceptible, and its hooks share that status while joined to it. Once removed from the couch, those hooks are no longer susceptible, since they have no standing as utensils in their own right; they are simply a dargash's hooks and nothing more.
"Veshel naklitin tehorah": on the bedposts, by contrast, the hooks stay tahor. Naklitin were a pair of upright poles, one placed at the head of the bed and one at its foot, each carrying a hook. A crossbar rested between the two hooks, and a canopy was spread over that crossbar. These poles are wooden utensils with no cavity, and they also lie outside tum'at midras, since nobody reclines on them. They can never contract tumah, and consequently their hooks are tahor even while still attached to them.
"Shel shiddah teme'ah": a chest's hook, the one from which the chest was suspended, is susceptible to tumah. A wooden chest is a straightforward container and is fully within the laws of tumah, so the hook that belongs to it becomes susceptible together with it.
"Veshel akon tehorah": with a fish trap the hook remains tahor. The akon was a wooden box with hooks mounted inside it; fish swimming in would snag themselves on those hooks. One might suppose that such a box counts as a keli kibul, yet as the close of the masechet clarifies, it was never meant to contain anything. Its only role is to hold the hooks in position so that fish get caught. Since the box lies beyond the reach of tumah, the hooks on it lie beyond it too.
"Veshel shulchan tamei": a table's hook, on which the table was hung while it stood unused, is susceptible to tumah. Even though a table is wooden and encloses nothing, it does become susceptible, because it renders direct service to people and to the vessels resting on it, and an object of that kind is susceptible without needing a cavity. Once the table is susceptible, the hook attached to it is susceptible along with it.
"Shel menorat ha'etz tahor": a wooden menorah's hook, used for hanging it up, is tahor. Since the menorah is beyond tumah, so is its hook. The menorah encloses nothing: the oil cups are separate items set on top of it. Nor does it resemble the table just discussed. The table acquired its susceptibility by serving people directly, whereas a menorah serves neither people nor vessels; it merely supports the lamp resting upon it. Wooden, without a cavity and without direct service, it stays tahor, and its hook with it.
The closing rule
The mishnah now states the principle on which every one of these rulings rests. "Zeh haklal: kol hamechubar letamei tamei," whatever is joined to something susceptible to tumah is itself susceptible, "vehamechubar latahor tahor," and whatever is joined to something that stays tahor remains tahor as well.
"Bechulan achat achat bifnei atzman tehorot," and in all these cases, each hook taken by itself is tahor. Even the hooks the mishnah declared susceptible hold that status only as long as they are joined to their keli. A hook standing alone has no name of its own; its whole identity is that it is the hook of a particular utensil, and once separated it carries no susceptibility. That is why these pieces of metal, on their own, are not subject to tumah at all.