The Gemara suggests: Come and hear a challenge to this principle from a mishna in tractate Kinnim (24a). A woman after childbirth must bring two bird offerings: A burnt offering and a sin offering. The mishna discusses a case where two women after childbirth, one of whom already brought her burnt offering and one of whom already brought her sin offering, bring their remaining offerings to the Temple, a sin offering for this one and a burnt offering for that one, but confusion has arisen as to which bird is which.

If the priest sacrificed both of them above the red line, half of the birds, i.e., one of them, is fit, as in any event the burnt offering has been sacrificed properly, and half of the birds, i.e., the other one, is disqualified. Likewise, if he sacrificed both of them below the red line, half are fit, as in any event the sin offering was sacrificed properly, and half are disqualified. If he sacrificed one above the red line and one below, they are both disqualified, as I say that perhaps the sin offering was sacrificed above, and the burnt offering was sacrificed below.

But according to Rav Adda bar Ahava’s explanation of Rabbi Yehoshua’s principle, the sin offering should be deemed fit in any event; even though the burnt offering was indeed sacrificed below the red line, it should be removed from its status as a burnt offering and become a bird sin offering.

The Gemara rejects this claim: It is reasonable to say that Rabbi Yehoshua stated his principle with regard to one person, whose offering the priest sacrificed below the red line instead of above it; but did he state it with regard to two people, one of whose offering the priest sacrificed for the sake of the other person? In the case of the two women, the priest sacrificed the offering for the sake of a different person altogether, and Rabbi Yehoshua would concede that such an offering does not become a sin offering.

The Gemara suggests: Come and hear another challenge from a mishna in tractate Kinnim (24a). The mishna discusses a case of two women who jointly brought three pairs of birds, as follows: The birds of one pair were designated as a sin offering and a burnt offering respectively, but it was not specified which woman’s obligation they were to satisfy; and the second pair was unspecified as to which bird was to be which offering; and the third pair was specified as to both the type of offering of each bird and whose obligation each bird was to satisfy.

If the priest sacrificed all of them above the red line, half of the birds are fit, as in any event the burnt offerings have been sacrificed properly, and half are disqualified. Likewise, if he sacrificed all of them below the red line, half are fit, as in any event the sin offerings were sacrificed properly, and half are disqualified. If he sacrificed half of every pair above the red line and half of it below, but it is unclear which bird he sacrificed above and which he sacrificed below, only the unspecified pair is fit, as by sacrificing one above and one below the priest has in effect designated them. And since the women brought the birds jointly, the fit pair is divided between them, one bird counting toward the obligation of each woman.

The mishna teaches that only the unspecified pair is fit, while the specified birds are not, as perhaps each bird was sacrificed on the wrong side of the red line and disqualified. But why should that be the halakha? According to Rav Adda bar Ahava’s explanation of Rabbi Yehoshua’s principle, even if the burnt offering was indeed sacrificed below the red line, it should be removed from its status as a burnt offering and become a bird sin offering.

And if you would say that this mishna is not in accordance with the opinion of Rabbi Yehoshua, how can you say that?

The Gemara explains: Come and hear evidence that the mishnayot in tractate Kinnim are in accordance with the opinion of Rabbi Yehoshua from another mishna in the same chapter (24b): The mishna discusses the case of a woman who said: It is incumbent upon me to bring one nest, i.e., one pair of bird offerings, if I give birth to a male child. Since all women who give birth must bring one pair of birds in any event, if she ultimately gave birth to a male, she must bring two nests, one for her vow and one for her obligation.

If she gave them to the priest without specifying which bird is to be which type of offering, the priest must sacrifice three above the red line and one below. This is because the obligatory pair must consist of a burnt offering and a sin offering, while a pair of birds brought to fulfill a vow must consist of two burnt offerings.

If the priest did not do so, but rather, thinking that both pairs were obligatory, sacrificed two above and two below, and he did not consult the woman before sacrificing them, she must bring one more bird [perida] and sacrifice it above the red line to satisfy her remaining obligation.

This is the halakha only if both pairs were of the same species of bird, either doves or pigeons; but if the two pairs were of two different species, and the priest does not remember which pair he sacrificed first, she must bring two more birds, one of each species. Whichever pair was sacrificed first is deemed the obligatory pair, and the woman must bring a bird of the other species to satisfy her remaining obligation of a burnt offering. But since it is not known which species of bird that is, she must bring one of each.

If the woman initially specified which species of bird she would bring for her vow but subsequently forgot what species she specified, and she then brought two pairs of a single species, and the priest mistakenly sacrificed two birds above the red line and two below, then she must bring three more birds, all as burnt offerings. One must be of the species she brought, to replace the bird mistakenly sacrificed below, and the other two must be of the other species, in case that was the species she specified in the first place.

This is the halakha only if both pairs that she brought were of the same species. But if they were of two different species, and the priest does not remember which pair he sacrificed first, she must bring four, two of each species. This is because no matter which species she specified, the priest may have sacrificed the pair of that species first, leaving none of that species to satisfy even part of her vow. She therefore may still need to satisfy an entire vow of either species.

The mishna continues: If, besides forgetting which species of bird she specified to bring for her vow, the woman also committed to sacrificing the birds of her vow together with the burnt offering of the obligatory pair, but the priest mistakenly sacrificed two birds above the red line and two below,