Nullified Impurity and the Threshold of Decomposition

How the Rambam defines the limits of ritual impurity in mixtures and decaying carcasses based on Bekhorot 23.

The Mixtures and the Putrefaction Debate

The Gemara on Bekhorot 23 explores two fundamental questions regarding ritual impurity. First, when an impure substance is nullified by a majority of pure substance, does it still transmit defilement through carrying without direct contact?

Second, at what stage of decay does an animal carcass lose its impurity entirely? Bar Padda maintains that severe impurity departs once the meat is unfit for a גֵּר תּוֹשָׁב (resident alien), while Rabbi Yoḥanan rules that it remains impure until unfit even for a dog.

Nullified in Touch but Defiling in Carrying

The Rambam rules that when meat of a carcass is mixed into a majority of ritually slaughtered meat, touching the mixture is pure. However, one who carries the entire mixture becomes impure.

He applies this identical principle to the ashes of the red heifer. If heifer ash is mixed into a majority of ordinary stove ash, the mixture does not defile through touch, but it defiles when carried.

נְבֵלָה שֶׁנִּתְעָרְבָה בִּשְׁחוּטָה אִם רֹב מִן הַשְּׁחוּטָה בְּטֵלָה הַנְּבֵלָה בַּשְּׁחוּטָה וְאֵין הַכּל מְטַמֵּא בְּמַגָּע. אֲבָל אִם נָשָׂא הַכּל נִטְמָא

When a carcass is intermingled with slaughtered meat, if the majority is slaughtered meat, the carcass is nullified and the whole mixture does not defile by touch; but if one carried everything, he is defiled. (Mishneh Torah, Other Sources of Defilement 1:17)

Defending the Distinction in Mixtures

The Ra'avad challenged the Rambam's rationale regarding mixtures, noting that the Talmudic discussion reflects the minority opinion of Rabbi Yehuda. The Kessef Mishneh answers that the Rambam wrote this to demonstrate that even according to Rabbi Yehuda nullification applies here, following Rav Ḥisda who was a later authority.

The Ri Korkos explains why carrying defiles while touching does not. In touching, each contact is isolated to an individual olive-bulk, but carrying lifts the entire volume simultaneously, thereby carrying the dispersed impurity.

The Threshold of Canine Inedibility

Regarding decomposing carcasses, the Rambam rules strictly in accordance with Rabbi Yoḥanan. Spoiled carcass meat remains impure until it is completely unfit for a dog to eat.

The Kessef Mishneh observes that although the Gemara leaves Rabbi Yoḥanan's view with a difficulty, it does not conclude with a refutation. Kiryat Sefer adds that consumption by a dog is halakhically deemed eating based on Scripture.

בְּשַׂר נְבֵלָה שֶׁנִּפְסַד וְהִבְאִישׁ וְנִפְסַל מִלֶּאֱכל הַכֶּלֶב טָהוֹר.

Carcass meat that decomposed, became putrid, and became unfit for a dog to eat is ritually pure. (Mishneh Torah, Other Sources of Defilement 1:13)

Exceptions and Wider Applications

If carcass meat decomposed before the animal died, it is pure from the start. The Rambam derives this from Deuteronomy 14:21, requiring the meat to be initially fit for human consumption.

This canine-edibility standard governs all other forms of defilement. The Rambam extends it to the carcasses of kosher fowl, dead creeping animals, and defiled foodstuffs.

Presumptions of Motherhood and Practice

In the concluding Mishnah, Rabban Shimon ben Gamliel teaches that mothers only nurse their own young. Codifying this rule, the Rambam states that one who discovers nursing mothers in a herd follows the presumption of maternal identity.

In practical halacha, ritual impurity persists in spoiled flesh as long as a dog would consume it. Furthermore, a majority nullifies impurity for contact, but carrying a mixture preserves liability for carrying defilement.

Impurity in mixtures is nullified for touch but remains active for carrying, while decaying carcasses retain defilement until completely rejected by dogs.

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