Keilim, Chapter 16, Mishnah 8. Our mishnah takes up a long list of cases, sheaths and coverings made of wood and of leather, and asks about each one whether it is a kli that can become tamei. The distinction that runs through the whole mishnah is a simple one, and it is spelled out at the end: an article built to hold something inside it is a receptacle and is susceptible to tumah, while an article built merely to cover something is not a receptacle at all and stays tahor.
The list starts with weapons and with the tools of trades. "Tik hasayif vehasakin vehapigyon": each of these blades had its own leather sheath, the sword, the knife, and the pigyon, a dagger honed on both of its edges. "Tik misporet umisparayim vehata'ar": here we have holders for metal implements used for cutting, the misporet, a pincers; misparayim, a pair of shears; the ta'ar, a razor.
From there the mishnah turns to smaller personal items. "Tik mikchol uvet hakechol": the slim case that holds the mikchol, the applicator used for painting the eyes, something like a mascara wand, and the kechol container itself, in which the cosmetic powder was kept. "Tik machtev": the little leather case for a stylus used for writing. "Veteruntek": a case divided into many compartments, capable of holding a whole assortment of different items at once.
"Tik tavla veskurteya": a tavla was a writing tablet of metal and a skurteya a wooden panel on which charts and tables were ruled, and each of them had a leather holder made for it. "Bet hachitzim, bet hapagoshot": the first of these carried ordinary arrows, while the second was made for arrows whose heads were broad.
Of all of these the mishnah concludes: "harei eilu temei'in," they are all susceptible to tumah. The reason is uniform. Every one of them has a genuine cavity into which its contents are placed, so every one of them is a receptacle, and a receptacle is a kli.
When the Opening Decides the Halachah
Next the mishnah presents an object whose ruling shifts with its design. "Tik simponya": the simponya was an instrument of music, and this is the case made for it. "Bizman shehu noten milema'ala, tamei": if the instrument is dropped in through an opening at the top, the case does receive tumah, since the simponya descends into a hollow space and the case thereby functions as a receptacle.
"Misido, tahor": but if the instrument slides in through an opening along the side, the case is tahor. In that construction the case is not functioning as a vessel that contains, it is functioning as a sheath that wraps around the instrument, and a wrapping is not a receptacle.
"Tik chalilin": a holder for chalilin, flutes. Regarding this holder we are told, "Rebbi Yehuda metaher mipnei shehu notno misido." Rebbi Yehuda declares it tahor, since the flute enters through the side. Loaded sideways rather than downward, the holder wraps the flute like a sheath instead of containing it like a vessel, and tumah therefore does not take hold of it.
Coverings for Weapons
"Chipui ha'ala, hakeshet veharomach": the covering of an ala, a club-like weapon topped with a spiked ball, the covering of a bow, and the covering of a spear. "Harei eilu tehorin," all of these are tahor. Each of them is fitted over the weapon to shield it, and none of them serves as a case that holds something within a cavity.
The General Rule
The mishnah closes by formulating the principle behind every ruling in the list: "Zeh haklal: he'asui letik tamei, lechipui tahor." Whatever is made to serve as a tik, a case into which an object is placed and held, is susceptible to tumah, because it qualifies as a receptacle. Whatever is made only as a chipui, a covering laid over an object to protect it, remains tahor, because it never becomes a receptacle at all.