Introduction Mishnayoth seven and eight both list cases in which one Sage declares something pure and the other Sages declare it impure.
Four cases of doubt Rabbi Joshua pronounces impure, and the Sages pronounce them pure. How is this so? If the impure person stands and the pure person passes by him; or if the pure person stands and the impure person passes by him; or if impurity is in the private domain and something pure is in the public domain; Or if something pure is in the private domain and something impure is in the public domain; If it is doubtful [in all of these case] whether one touched or did not touch the other, or if it is doubtful whether one formed a tent over the other or did not form a tent over the other, or if it is doubtful whether one moved or did not move the other Rabbi Joshua pronounces such a case impure, and the Sages pronounce it pure. In this mishnah are listed four situations in which there is a doubt whether or not the pure person was touched by the impure person, or one of them formed a tent over the other (which would cause impurity to be transmitted, even without contact) or one of them moved the other (which would also transmit impurity, even without contact). In all of these situations Rabbi Joshua rules that the previously pure person is now impure, whereas the Sages hold that he is still pure. The cases are: i + ii) A case where one of the people is moving and one is stationary. In this case Rabbi Joshua pronounces the person impure due to the general rule that doubtful cases of impurity which occur in the private domain are ruled impure. The Sages say that he is pure. Although there is a general rule that doubtful cases of impurity that occur in the private domain are ruled impure, this is true only when the pure and the impure are either both moving or both stationary. If their status is different, then the rule is not applicable. iii + iv) The pure and impure are in different domains, one in the public domain and one in the private domain. According to Rabbi Joshua, since at least one of the two is in the private domain, he is impure, due to the above mentioned rule. According to the Sages, since one is in the public domain, the rule that doubtful cases of impurity in the private domain does not apply.