Ohalot, Chapter Eleven, Mishnah One
1) A house, which has been split [into two]:
2) If there is uncleanness in the outer [part], vessels in the inner [part] remain clean.
3) If the uncleanness is in the inner [part], vessels in the outer [are clean]:
a) Bet Shammai says: when the split is four handbreadths wide;
b) But Bet Hillel says: [when the split is of] any size.
c) Rabbi Yose says in the name of Bet Hillel: [when it is] one handbreadth wide.
Section one: Our mishnah deals with a house that has been split entirely into two.
Section two: If there is impurity in the outer part of the house, in the part that is closest to the doorway, it doesn’t travel in and defile the vessels that are in the inner part of the house. This is because of the rule that impurity goes out but does not come in.
Section three: If the impurity is in the inner part of the house, the two houses debate how large the split must be for it to escape and not defile the vessels that are in the outer part.
Beth Shammai says that the opening must be at least four handbreadths wide for impurity to escape.
Bet Hillel says that the split can be of any size.
Rabbi Yose presents a different version of Bet Hillel’s opinionthe split must be at least a handbreadth. Smaller than that and the impurity will travel through the outer part of the house and defile the vessels there as well.