While the Mishnah that was discussed on yesterday’s daf (=page) focused on someone who makes simultaneous statements sanctifying a pregnant animal and it embryo, the following Mishnah presents a case where the owner of two sanctified animals – an olah (burnt offering) and a shelamim (peace offering) – tries to switch one (or both) of them by means of temurah.
According to the Mishnah, 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 should switch the olah, should switch the shelamim,” we accept his first statement and the animal becomes an olah. Rabbi Yose says that if he really intended for the animal to switch both, recognizing the fact that a person cannot say both things simultaneously we give the new animal the status of half-olah, 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 halakhah allows it to be redeemed, we will require that the owner redeem it and with half of the proceeds purchase an olah and with the other half purchase a shelamim. If, however, he changed his mind when he made his second statement (“this animal should switch the shelamim“), then only the first statement is meaningful, and the animal will become an olah.
Rabbi Yitzhak b’Rabbi Yose quotes Rabbi Yohanan 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 switch the olah, and then it should switch the shelamim,” even Rabbi Yose would rule like Rabbi Meir.
It should be noted that when this Mishnah is discussed in Massekhet Zevahim (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 Yose. 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.