Keilim, Chapter 23, Mishnah 4. Our chapter continues to examine which objects are candidates for tum'at midras, the tum'ah that a zav (and others like him) transmits by pressing his weight upon an item designated for lying or sitting. The question in each case is not what the object looks like, but what it is for: does it serve a person as a place to lie down (mishkav) or to sit (moshav)?
The Mishnah begins: "Hamitah vehakar vehakeset shel met, harei eilu temei'in midras" - the bier, the pillow and the cushion belonging to a corpse are susceptible to tum'at midras. These are the items prepared for a body that is being carried out to the funeral and to burial: the stretcher on which he is laid, together with the pillow and the cushion placed beneath him. Should a zav lean his weight on them, they contract tum'at midras.
Why should that be so? Here we reach the principle that drives the entire ruling. The fact that a dead body rests upon an object contributes nothing at all to its classification for the laws of tum'ah and taharah. Had these items been fashioned purely so that a corpse should lie on them and for no other purpose, they would never enter the category of mishkav or moshav in the first place. What determines the matter is the service the object renders to a living person.
And that service exists here. When the women gather to mourn, they lean upon the bier and upon the pillow and cushion that lie on it. Through that ordinary human use, these very items become objects upon which a living person supports himself, and once that is true they take their place among the utensils designated for lying and sitting. That is precisely why the zav who presses upon them renders them tamei with tum'at midras.
Three seats are now listed. The first is "kisei shel kallah", the chair on which a bride is seated during her wedding. The second is "mashber shel chayah", the stool used by a woman in labor, on which she sits while her child is born. The third is "kisei shel koves", the seat belonging to a launderer, which the Mishnah identifies by the words "shekormim alav et hakeilim". Its construction resembles a low table fitted with a flat plank across its top, and once the washing is finished the launderer lays the garments out on that plank, folding them and pressing them into shape.
Of all three the Mishnah records a ruling: "amar Rebbi Yose", and his verdict is "ein bahem mishum moshav", none of them carries the status of a seat for these laws. They simply are not seats in the plain sense of the word, for a person does not lower himself onto any of them in order to rest. In each case the sitting serves a goal outside itself: the bride is placed on her chair as part of the proceedings of the wedding, the woman in labor uses the mashber to assist the birth, and the launderer takes his place on his seat only because the work demands that he bring his weight down upon the fabric.
Since sitting on these objects is a means to an end rather than the resting that defines a seat, Rebbi Yose holds that they are not counted as utensils made for sitting. Consequently, even if a zav sits upon them, they do not become tamei as a moshav. The two halves of our Mishnah thus teach one lesson from two directions: a bier made for the dead can still be a mishkav because living people lean on it, while a chair that living people certainly sit on may still not be a moshav, because that sitting is not the restful use for which seats are made.