The Talmud becomes more challenging when we encounter rabbinic concepts that have no perfect analogue or translation into English. The concept of “like substances” on today’s daf is a good example. Unfortunately, we don’t have better English words to describe this concept, so as you read this piece, please hold onto the idea that the term “like substances” doesn’t necessarily mean exactly what your English-language brain thinks it means.
To make matters more complicated, even the rabbis don’t agree on what it means. The Talmud has been discussing nullification: When two items of different ritual statuses are mixed (permitted with forbidden, pure with impure, etc.), one substance can sometimes nullify the other, causing the mixture to take on a single status. For example, if one accidentally drops a tiny amount of milk into a vat of meat stew, the meat stew will nullify the milk and the stew is still considered kosher, even though mixing meat and milk is forbidden.
On yesterday’s daf, we encountered a debate between Rabbi Yehuda and the rabbis about nullification. Rabbi Yehuda stated that “like substances” can never nullify one another. The rabbis agreed that like substances cannot nullify one another so that the mixture can be offered on the altar, but stated that in other circumstances they might nullify one another.
Today’s Gemara offers a third perspective, from Rav Hisda, on whether like substances can nullify one another. Here is his opening statement:
Rav Hisda says: The meat of an unslaughtered animal carcass is nullified in meat of a slaughtered animal, because meat from a slaughtered animal cannot attain the status of a carcass.
An unslaughtered animal carcass (neveilah) imparts impurity, whereas properly slaughtered meat (shechuta) does not. Rav Hisda asserts that if a small amount of neveilah meat is mixed with a large amount of shechuta meat, the neveilah is nullified, and one who touches the mixture is not rendered impure.
Neveilah and shechuta are both meat, and therefore we might assume they are considered to be like substances. But Rav Hisda, in stating that neveilah can be nullified by shechuta, suggests the two are not like substances. Why would he think this? Because although both are meat, they have different ritual potential. Shechuta meat will never become impure like neveilah. But neveilah can rot and lose its impurity, rendering it more similar to shechuta. This ritual distinction is sufficient to consider these meats two different substances. The result, according to Rav Hisda: A large amount of shechuta meat can nullify a small amount of neveilah meat, rendering it pure.
Rav Hisda then presents the opposite case:
Meat of the slaughtered animal is not nullified in meat of the carcass, as it is possible for a carcass to attain the status of a slaughtered animal, because when a carcass rots, it loses its impurity.
If a small amount of shechuta meat is mixed with a large amount of neveilah, the neveilah meat cannot nullify the shechuta meat, assimilating the whole mixture to neveilah status. This is because, as previously explained, neveilah could “become shechuta” in the sense that if it rots beyond edibility it is no longer impure. Therefore, even in its fresh state, it is considered to be a like substance.
So, according to Rav Hisda’s view, the question of whether neveilah and shechuta are treated as like substances depends on which is present in larger quantity in a mixture of the two. This is mind-bending if you think that two things either are alike or they are not. But according to Rav Hisda, if the substance that could never take on the other’s identity is the majority (i.e., the shechuta), then it’s considered to be a mixture of different substances. And if the substance that could take on the other’s identity is the majority (i.e., the neveilah), then it’s considered a mixture of like substances.
The Gemara goes on to point out that Rav Hisda’s halakhah, at first glance, does not appear to follow either the rabbis or Rabbi Yehuda from yesterday’s daf. Let’s focus on the latter. Rabbi Yehuda thinks that like substances never nullify one another, and it turns out that he defines what constitutes “like substances” a little more intuitively. For Rabbi Yehuda, since shechuta and neveilah are both meat, he considers them like substances, regardless of the proportions in which they are mixed. Rabbi Yehuda is conceptualizing these mixtures by their physicality and appearance. By contrast, for Rav Hisda on today’s daf, the relevant factor is their ritual functions or potentials, leading to the possibility that their likeness is determined by the majority substance in the mixture. Ultimately, this gives us two very different definitions of “like substances.”
Read all of Menachot 21 on Sefaria.
This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on February 3, 2026. If you are interested in receiving the newsletter, sign up here.
