Machshirin, Chapter 2, Mishnah 10. The closing mishnayos of this chapter apply the principle of rov, following the majority, to items whose origin we cannot trace. Here the subject is produce, and the question is not whether it is permitted to eat, but whether trumos and maasros have already been separated from it.
"Hamotzei peiros baderech": one who comes upon produce lying on the road. If "rov machnisin l'bateihen," most people take such produce into their houses, then he is "patur." But if "k'vod hashuk," the local practice is to bring it to the marketplace, he is "chayav."
The case
A person finds produce lying along the road. The Mishnah is speaking of produce that carries no siman, no identifying mark by which an owner could claim it, so it need not be returned and the finder may keep it. The only issue left is its maaser status.
The Torah obligation and the rabbinic expansion
By Torah law the maaser obligation takes hold only once the produce has been brought inside the owner's home; before it crosses that threshold there is no d'oraisa duty to tithe. The Chachamim, however, extended the obligation to an earlier stage. From the moment produce is removed from the field, its treatment depends on where it is headed. Produce on its way to the marketplace to be sold may not be eaten at all before trumos and maasros are taken from it. Produce on its way home may still be nibbled at casually, though not eaten as part of a set meal.
Applying the majority
With that in mind, the Mishnah's ruling follows naturally. If most people in that place bring their produce home rather than to the market, we assume this produce was on its way to someone's house. Maaser had not yet been taken from it, but it had also not yet entered a house, so the finder is patur and may snack from it.
With this in place, the ruling of the Mishnah is straightforward. Where the practice of the majority is to carry produce home rather than to sell it, we presume that this produce too was en route to somebody's house. Maaser had not yet been removed from it, but neither had it ever crossed a doorway, so the finder carries no obligation and may snack on it.
"Mechtzah l'mechtzah, demai." Where the two practices are evenly divided, the produce falls into the status of demai: produce about which we cannot determine whether trumos and maasros were separated. There is an entire masechta devoted to this category and its halachos.
A storehouse used by Yisroel and nochri together
"Otzar," a storehouse, "sheYisroel v'nochri matilin l'socho," into which both a Yisroel and a nochri deposit produce. "Im rov nochrim, vadai." "Im rov Yisroel," the ruling is "demai." And "mechtzah l'mechtzah, vadai, divrei Reb Meir."
The case is a storehouse into which both a Yisroel and a nochri deposit their produce, and the contents have become mixed together so that one cannot tell whose is whose.
Reb Meir rules that if the majority of the produce came from the nochri, the whole store is vadai tevel, definitely untithed, and no one may eat from it until maasros are taken. This flows from Reb Meir's position elsewhere in the Mishnah that a nochri's acquisition of land in Eretz Yisroel does not remove the produce from the obligation of maaser. Produce grown in a nochri's field is therefore fully obligated, and the nochri certainly did not separate anything from it. Since the majority of the pile is his, we treat the entire mixture, by the principle of rov, as untithed tevel.
If the majority came from the Yisroel, the status is demai. Some of what is in the storehouse certainly requires maaser and was never tithed, and it has all been blended together, so we cannot say the produce is clean; we treat the whole of it as being in a state of doubt, with all the halachos of demai.
If it is half and half, Reb Meir rules vadai. There is no majority here to neutralize the nochri's portion, so the entire quantity is treated as certain tevel.
The view of the Chachamim
The view of the Chachamim
"V'Chachamim omrim": the Sages disagree. "Afilu kulam goyim," even where every one of the depositors is a nochri, "v'Yisroel echad matil l'socho," and just one solitary Jew has put produce inside, the ruling is "demai." In their view the status can never be worse than doubtful, no matter how lopsided the mixture is toward the nochri's grain.
Their position rests on the reverse premise: the Rabbanan maintain that when a nochri owns land in Eretz Yisroel, its crop is exempt from tithes altogether, so whatever he grows bears no maaser requirement. Had that storehouse contained nothing but his produce, there would have been nothing at all to separate. It is the single Jew's share that generates the uncertainty, and that uncertainty is sufficient to give the entire mixture the standing of demai. Certain tevel, though, it can never become, since nearly all of what is stored there was never subject to tithes in the first place.
So this Mishnah teaches us how the principle of rov shapes maaser obligations twice over: in deciding the likely destination of produce found on the road, and in resolving the status of a mixture whose owners cannot be sorted out.