Taharos, Chapter 4, Mishnah 10. Our chapter has been working through lists of sfeikos: first a list of doubtful cases that we rule tamei, and then a list of doubtful cases that we rule tahor. In the middle of that second list the Mishnah pauses for a moment. Before continuing the enumeration, it records a dissenting voice: Rabbi Yose, who takes issue with a ruling stated earlier in the chapter. There we learned that liquids convey tumah only on the level of d'rabbanan. Rabbi Yose disagrees, at least in part, and this Mishnah is his brief detour.
The Rule of Rabbi Yose
Rabbi Yose's principle comes in two short clauses, and everything depends on the object that the liquid may have reached. "Safek mashkin," a doubt involving liquids, is ruled one way when the item in question is food and another way when it is a utensil. Picture liquids that are tamei, and now a question arises: did they or did they not make contact with a person's foodstuffs? For such a case the ruling is "la'ochlin tamei": the food is declared tamei. The reasoning is that Rabbi Yose holds the power of liquids to impart tumah to food to be Torah law, d'oraisa, and an unresolved doubt in a d'oraisa matter is decided by the stricter possibility.
"La'kelim tahor." Where the question is whether those same liquids touched a vessel, Rabbi Yose concedes that the tumah of liquids toward kelim is only rabbinic. A doubt in a matter of d'rabbanan is treated leniently, and the vessel remains tahor.
The Illustration
"Keitzad? Shtei chaviyos, achas t'mei'ah v'achas tehorah." How does this work in practice? A person has two jars standing before him. One is filled with water that is tamei, the other with water that is tahor.
"V'asa isah me'achas meihen." He took water from one of the two jars and used it to knead dough. "Safek min hat'mei'ah asah, safek min hatehorah asah." Afterward he cannot recall which jar he drew from. It may have been the tamei water and it may have been the tahor water; the matter is a complete doubt.
"Zehu safek mashkin la'ochlin tamei v'la'kelim tahor." This, says the Mishnah, is precisely the case Rabbi Yose has in mind. The doubt concerns liquids and food, and therefore it is decided stringently. The practical outcome for the person standing with his mixing bowl is that his dough, the challah he is preparing, is treated as tamei. Had the identical doubt arisen regarding a vessel rather than food, the ruling would have gone the other way, and the vessel would have stayed tahor.
With that, Rabbi Yose's dissent is recorded, and the Mishnah is ready to return to its list.