Ohalos, Chapter 9, Mishnah 14. This is the closing mishnah of the entire sugya of the kveres, the beehive, which has occupied a long stretch of this perek. Like several other mishnayos here, it opens with the words "Bameh devarim amurim," in what circumstances was the previous ruling stated? In other words, the Mishnah now comes to limit the halachah we learned until now and to tell us that under different conditions the outcome changes entirely.
To grasp what is being narrowed here, we have to recall the case that came before it. The perek has been discussing a beehive left outdoors, standing on its base with its opening turned toward the sky, and, most importantly, one that is still a complete, usable vessel. About such a kveres we learned: as long as it sits flush on the ground without a tefach of clearance under it, then no matter where the tumah is located (below the kveres, within it, or resting on its top) the tumah is bokaas v'olah and bokaas v'yoredes, it breaks through upward and it breaks through downward. Tumah lying below rises vertically, and anything standing in that vertical column becomes tamei, an object placed inside the hive included. Tumah resting above descends vertically, and once again whatever is caught in that column, even within the hive, becomes tamei. Objects to either side, however, are left untouched.
Change any of those details and the halachah shifts. Suppose this upright hive was propped up so that a tefach separated its floor from the earth, creating an ohel below; or a cover was laid across its opening; or it was inverted, so that its base now served as a roof overhead. In each of these arrangements, tumah below, tumah within, or tumah above no longer moves in a bare vertical column. The ohel carries it laterally, and as soon as the tumah has filled the entire breadth of the hive it rises and drops throughout. All of this held true precisely because the object under discussion was a real vessel, and a vessel offers no barrier to tumah.
The Mishnah's Limitation
Now our Mishnah opens: "Bameh devarim amurim, bizman shehu keli," all of the above was taught only when the kveres has the status of a functioning vessel. "Aval hayesa pechusa u'fekukah bekash" - but if it was breached at the bottom, and even though he plugged up the hole with straw, that stopping-up does not restore it to being a keli. "O machzekes arba'im se'ah k'divrei chachomim" - or it holds forty se'ah, which brings us back to the principle we met earlier: a vessel of that capacity is not susceptible to tumah at all, and the chachomim hold that just as it is not a keli for becoming tamei, it also does not carry the din of a keli that fails to block tumah. Such a kveres can indeed block tumah.
What follows in either of these cases? "Tumah tachtehah, b'sochah, o al gabah" - whether the tumah is beneath the kveres, inside it, or on its top, once again the tumah is bokaas v'olah and bokaas v'yoredes. It cuts straight through, rising or descending, and renders tamei whatever lies directly in its path, but it does not spread off to the sides.
The first Tanna, then, arrives at exactly the result we already had. Whether the hive still qualifies as a vessel or has lost that status, once it is standing on its base outdoors, seated directly on the earth with no clearance of a tefach below, the tumah drives a vertical path up or down and defiles whatever it meets along that path.
A Dissenting Ruling: Reb Shimon and Rebbi Eliezer
The chiddush of this Mishnah lies in the second opinion recorded at its end: "Rebbi Eliezer v'Reb Shimon omrim." Speaking of that same hive, one that has forfeited the standing of a vessel and whose base rests directly on the earth, these two Tannaim rule: "ein tumah olah lah v'af lo yoredes mimena." Should a kezayis of a corpse lie below the hive, the tumah will not ascend into its interior; and should the kezayis be lying within the hive or upon its top, the tumah will not travel down past the floor of the hive.
They rule this way even where not a single tefach separates the hive from the earth. Since this kveres has forfeited the status of a vessel, either through the breach in its bottom or, as the chachomim maintain, because of its forty-se'ah capacity, it takes on something of the nature of an ohel, and it therefore seals off the tumah, preventing it from moving between the space below and the space within.
When There Is a Tefach Beneath
The Mishnah continues: "Hayesa gevohah min ha'aretz tefach." Now picture this same kveres, standing upright in the open air, one that is not a keli (either breached or, according to the chachomim, holding more than forty se'ah), but this time it is not resting directly on the ground. There is a full tefach of space between the floor and the bottom of the kveres.
"Tumah tachtehah, tachtehah tamei." With the tumah lying below, the entire area below is rendered tamei, since that tefach of clearance constitutes an ohel by itself, and an ohel distributes tumah across its full extent. Whatever rests above the hive, though, stays tahor: the same ohel that carries the tumah sideways beneath also does the work of a true ohel in pinning the tumah down so that it cannot climb.
"B'sochah o al gabah, knegdo ad harakia tamei." Where the kezayis lies within the hive or upon its top, everything in the column above the tumah, right up to the heavens, becomes tamei, since there is nothing overhead to press it down. Only that column is affected, though. Whatever stands to one side, including items sitting in the hive itself, is tahor: the tefach of clearance produces an ohel underneath the hive alone, whereas the interior of the hive, whose top is open, and all the more so the space overhead, has no covering to carry the tumah outward.
One detail deserves to be filed away: that tefach separating the earth from the underside of the ohel works in two directions, both stringently and leniently. Stringently, in that tumah situated below is diffused across the whole space under the hive. Leniently, in that tumah situated in the hive makes no descent whatsoever, not so much as a vertical one. A vessel placed squarely under the kezayis that lies in the hive, provided it is positioned beneath the hive, is tahor, for a legitimate ohel stops tumah in its tracks.
Reviewing the Cases
Every case here involves a hive left outdoors with its opening turned upward. Where it remains an intact vessel and sits on the earth with no tefach of clearance, the tumah moves along a single vertical column, up or down, and items to the sides are tahor. Where it remains an intact vessel but a tefach separates its base from the earth, everything is rendered tamei, the areas to the sides included.
To these our Mishnah appended a hive whose bottom was broken through; stuffing the hole with straw does not win back its status as a vessel, though it still stands on its base on the earth in the open. For the first Tanna, with no tefach of clearance below, only whatever falls within the vertical column of the tumah contracts tumah.
Reb Shimon and Rebbi Eliezer chart a different course. When the tumah is under such a hive, the space under it is tamei, yet whatever sits in the hive is tahor even if it stands squarely over the tumah. In the reverse case, a kezayis within the hive or upon it renders tamei only what is aligned with it, in the hive or overhead, while the space below is tahor, even the spot immediately under the kezayis. And they say this even in the absence of any tefach of clearance underneath.
Lastly, when a tefach of clearance does lie beneath such a hive, one lacking the standing of a proper vessel, every opinion converges. A kezayis below defiles the whole space under the hive, the sides as well, since the ohel disperses it, while the interior and the area overhead stay tahor even where they face the kezayis directly. And a kezayis within the hive or upon it defiles whatever is aligned with it inside or above, leaving the space below tahor even at the point right under the kezayis, because the tefach underneath creates an ohel that holds the tumah in check.