The Gemara asks: But with regard to sacrificial animals it is also stated in the first part of the verse: “A bull or a sheep” (Leviticus 22:27), which are two animals from which you cannot produce diverse kinds. And accordingly, let us include an animal of diverse kinds as being fit for sacrifice on the altar on that account. The Gemara answers: From the fact that the latter clause of the verse: “Or a goat,” serves to exclude a type of animal from being fit for sacrifice on the altar, it may be inferred that the first clause: “A bull or a sheep,” also serves to exclude a type of animal from being fit for sacrifice on the altar. The Gemara asks: On the contrary, one could equally argue that from the fact that the first clause of the verse serves to include a type of animal as being fit for sacrifice on the altar, the latter clause also serves to include a type of animal as being fit for sacrifice on the altar.

The Gemara rejects this argument: What is this comparison? Granted, if you say that both expressions serve to exclude types of animals from being fit for sacrifice on the altar, this is why two exclusions were necessary: One exclusion is referring to diverse kinds and the other is referring to an animal that resembles another species, as even though an animal of diverse kinds is excluded, it was still necessary to exclude an animal that resembles another. But if you say that both phrases serve to include types of animals as being fit for sacrifice on the altar, why are two inclusions required? Now that an animal of diverse kinds has been included, in the first inclusion, is it necessary to say that an animal that resembles another is also included? There is more justification for including an animal that resembles another, whose parentage is entirely of one species, than for including an animal of diverse kinds.

The Gemara has established that when the Torah uses the word seh (Exodus 21:37) in the context of theft it does not serve to exclude animals of diverse kinds. The Gemara asks: If so, what is meant by this statement that Rava says with regard to the verse: “The ox, the seh of a sheep, and the seh of a goat” (Deuteronomy 14:4), that this establishes a paradigm for other cases, teaching that wherever the word seh is stated in the Torah, it serves to exclude only an animal of diverse kinds. With regard to what halakha did Rava state this principle? If this principle is referring to the halakha concerning sacrificial animals, it is written explicitly with regard to them: “A bull or a sheep” (Leviticus 22:27), which, as taught in the aforementioned baraita, serves to exclude diverse kinds.

If this principle is referring to the halakha concerning animal tithe, concerning which it is written: “And all the tithe of the herd or the flock [tzon], any one that passes under the rod, the tenth shall be sacred unto the Lord” (Leviticus 27:32), this principle is not necessary either. The reason is that the exclusion of diverse kinds can be derived by means of a verbal analogy from the term “under” in this verse, and the word “under” in a verse that deals with sacrificial animals: “When a bull, or a sheep, or a goat is born, it shall be seven days under its mother” (Leviticus 22:27). This verbal analogy, from which many halakhot of animal tithe are derived, indicates that diverse kinds are not subject to animal tithe, just as they cannot be used for an offering.

If this principle is referring to firstborn animals, concerning which it is written: “However, the firstborn among animals, which is born as a firstling to the Lord, no man shall sanctify it; whether it be ox or seh, it is the Lord’s” (Leviticus 27:26), it is not necessary in that context either. The reason is that this can be derived by a verbal analogy between the term passing, in the verse: “And you shall cause to pass to the Lord all that open the womb” (Exodus 13:12), and the same term passing, from a verse concerning animal tithe: “And all the tithe of the herd or the flock, any one that passes under the rod, the tenth shall be sacred unto the Lord” (Leviticus 27:32). This verbal analogy teaches that if the firstborn of a ewe or a she-goat is an animal of diverse kinds it is not considered a firstborn with regard to the halakhot of firstborn animals, which means that Rava’s principle is not necessary here.

Alternatively, you must say that an animal that resembles another is not subject to the halakhot of a firstborn, as it is written: “But the firstborn of a bull, or the firstborn of a sheep, or the firstborn of a goat, you shall not redeem; they are holy” (Numbers 18:17). This indicates that the halakhot of the firstborn are not applicable unless the fathering animal is a bull and its firstborn is also a bull. This excludes an animal that resembles another species, rather than its father. Once it is established that an animal that resembles another is not subject to the halakhot of a firstborn, is it necessary for the Torah to state the same with regard to diverse kinds? Since it is evident that firstborn status does not apply to diverse kinds, Rava’s principle is not required here either.

Rather, Rava’s principle was stated with regard to the redemption of a firstborn donkey, concerning which it is written: “And every firstborn of a donkey you shall redeem with a seh” (Exodus 13:13), as we learned in a mishna (Bekhorot 12a): One may not redeem a firstborn donkey neither with a calf, nor with a non-domesticated animal, nor with a slaughtered animal, nor with a tereifa animal, nor with diverse kinds, i.e., a sheep-goat hybrid, nor with a koy. Rava’s principle is referring to the source for the prohibition against using an animal of diverse kinds for the redemption of a firstborn donkey.

The Gemara asks: But what about according to the opinion of Rabbi Elazar, who disagrees with this ruling and permits the use of an animal of diverse kinds for the redemption of a firstborn donkey? As we learned in the same mishna: Rabbi Elazar permits diverse kinds for use in the redemption of a firstborn donkey because it is considered a seh. Accordingly, with regard to what halakha is Rava’s principle relevant?

Rabbi Elazar could have said to you: Rava’s principle was stated with regard to a non-kosher animal that was born from a kosher mother, whose impregnation was from a non-kosher animal. Rava is saying that this animal is not kosher. And this is not in accordance with the opinion of Rabbi Yehoshua, as, if it were in accordance with the opinion of Rabbi Yehoshua, although he would agree with this halakha, he derives this halakha (see Bekhorot 7a) from the phrase: “The seh of sheep [kevasim], and the seh of goats [izzim]” (Deuteronomy 14:4). The plural forms “kevasim” and “izzim” indicate that a lamb is not kosher unless both its father is a sheep and its mother is a ewe, and the same halakha applies to a kid.

The Gemara asks with regard to the case under discussion: But can a kosher animal become impregnated by a non-kosher animal in the first place? Is it even possible for this to occur? Why did Rabbi Yehoshua and Rava have to find a biblical source to deem this offspring as non-kosher? The Gemara answers: Yes, it is possible. As we maintain elsewhere (Bekhorot 7a)