While the Mishna that was discussed on yesterday’s daf focused on someone who makes simultaneous statements sanctifying a pregnant animal and it embryo, the following Mishna presents a case where the owner of two sanctified animals – an ola (burnt offering) and a shelamim (peace offering) – tries to switch one (or both) of them by means of temura.
According to the Mishna, Rabbi Meir says that in such a case, where a single animal is positioned to replace one of the sanctified animals, and the person says “this animal is hereby the substitute of the ola, the substitute of the shelamim,” we accept his first statement and the animal becomes an ola. Rabbi Yosei says that if he really intended for the animal to substitute for both, recognizing the fact that a person cannot say both things simultaneously we give the new animal the status of half-ola, half-shelamim. Since such an animal cannot be sacrificed, we wait until it develops a blemish that would render it unfit for sacrifice. At that time, when halakha allows it to be redeemed, we will require that the owner redeem it and with half of the proceeds purchase an ola and with the other half purchase a shelamim. If, however, he changed his mind after making the first statement (and then said “this animal should substitute for the shelamim“), then only the first statement is meaningful, and the animal will become an ola.
Rabbi Yitzḥak b’Rabbi Yosei quotes Rabbi Yoḥanan as teaching that all would agree to the principle of tefos lashon rishon – accept the first statement – so if the person said “this animal should substitute for the ola, and then it should substitute for the shelamim,” even Rabbi Yosei would rule like Rabbi Meir.
It should be noted that when this Mishna is discussed in Massekhet Zevaḥim (30b) the Gemara does not raise tefos lashon rishon as significant, and, indeed, appears to assume that the principle is rejected by both Rabbi Meir and Rabbi Yosei. The assumption of that Gemara is that they differ on how to understand the intention of the person who is making these statements and the subjective question of whether or not the person changed his mind.