Majorities, Presumptions, and Firstborn Animals

How Tosafot clarifies when halakhah follows statistical majorities and when an existing presumption forces us to consider the minority.

Purchasing an Animal From a Gentile

When an Israelite buys an animal from a gentile, the status of its future offspring is uncertain. If the mother already gave birth in the gentile's domain, the next newborn is not a firstborn (bekhor). Most animals conceive in their first year, so statistically the animal likely gave birth already.

Yet the Sages treat the offspring as an uncertain firstborn. Ravina explains that the Sages do not follow a majority dependent upon an action. As Rashi clarifies, animal pregnancy requires copulation, and we suspect that a male never mounted her.

כגון עיבור הבהמה דתלי בהרבעה ואיכא למיחש שמא לא עלה עליה זכר הילכך ספק

For example, the pregnancy of an animal, which depends on mating, and there is reason to be concerned that perhaps a male did not mount her; therefore, it is uncertain. (Rashi on Bekhorot 20a:2:1)

Human Intercourse Versus Animal Mating

Tosafot is troubled by a sugya in Yevamot. A widow must wait before marrying because her deceased husband's co-wife might be pregnant. Why did the Gemara not resolve that case by saying pregnancy depends on an action?

Tosafot answers that human intercourse occurs naturally without external intervention. By contrast, animals often require human assistance to mate properly. Therefore, human pregnancy is not categorized as dependent upon an action.

דתשמיש דאדם לא חשיב תלי במעשה כמו תשמיש דבהמה דפעמים דבהמה צריך להרביע

Human intercourse is not considered dependent upon an action in the same way as animal intercourse, for sometimes an animal requires human intervention to mate. (Tosafot on Bekhorot 20a:2:1)

Rabbi Yehoshua and Murky Discharges

The Gemara notes that an early murky discharge (tinuf) exempts subsequent births from firstborn status. Rabbi Yehoshua suspects that such a discharge occurred. Tosafot asks how Rabbi Yehoshua could suspect this outcome. Most animals do not discharge murkily, and this animal has a presumption (chazakah) of never having given birth.

Against both a majority and a presumption, a discharge is a minority of a minority. Even Rabbi Meir ignores such a slender possibility. Tosafot answers that the owner holds a monetary presumption is stronger than the majority, placing the burden of proof on the priest. Alternatively, because most animals conceive once mature, that general fertility supports the suspicion of discharge.

דהיכא דאיכא רובא וחזקה הוי המיעוט מיעוט דמיעוטא והכא איכא רובא דאין מטנפות וחזקה שהיא בחזקת שלא ילדה

Wherever there is a majority and a presumption, the minority is a minority of a minority; and here there is a majority that do not expel a murky discharge, and a presumption that it has not given birth! (Tosafot on Bekhorot 20a:7:1)

Presumption Supporting the Minority

The Gemara asks whether milk production alone exempts the subsequent newborn from firstborn sanctity. Most animals produce milk only after giving birth, but a minority lactates without having given birth. Rabbeinu Tam rules that milk alone does not exempt the offspring.

Rabbeinu Tam explains that a presumption supports the minority here, because the mother starts with a presumption of never having given birth. When an existing presumption reinforces the minority, we must fear a minority status stringently. Consequently, the newborn remains an uncertain firstborn rather than fully exempt.

והכא איכא חזקה דהעמד בהמה בחזקת שלא ילדה וסמוך מיעוטא דחולבות ואע"פ שאינן יולדות לחזקה

And here there is a presumption: establish the animal upon its presumption of not having given birth, and join the minority of those that lactate even though they do not give birth to the presumption. (Tosafot on Bekhorot 20b:4:1)

When an established legal presumption reinforces a statistical minority, halakhah treats that minority with strict stringency.

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