Clarification: The Ri explains that this is a Machlokes in'ha'Techeiles' (Menachos 49.).

Clarification: Why does Rebbi Yehoshua then say that he changed its name to something that is forbidden'? Even if he changed it to something that is permitted, he ought to be Chayav, since he has uprooted it?

Question: The Rashba asks, that even if we were to establish it entirely by where he erred, Rebbi Yehoshua would have to be referring to the words of Rebbi Eliezer, since, according to him (Rebbi Yehoshua), in the Reisha he would be Chayav, even if he changed to something that ist permitted, since he did not perform a Mitzvah ...

Question (cont.): Seeing as we establish our Mishnah like Rebbi Shimon, who holds in Perek RebbiEliezer de'Milah (Shabbos, Daf 137.) that according to Rebbi Yehoshua, if one did not perform a Mitzvah, one is Chayav ...

Source: Because Rebbi Shimon states that 'Rebbi Eliezer and Rebbi Yehoshua do not argue over two babies, one to circumcise after Shabbos, and the other, on Shabbos, and he forgot and circumcised the Sunday baby on Shabbos, that one is Chayav, since he did perform a Mitzvah'.

Question (Concl.): That is why the fact that one needs to say that the Reisha speaks where he changed to something that is Asur, it must be according to Rebbi Eliezer, because, according to him, in the Seifa too, he did not perform a Mitzvah, since he invalidated earlier, where one Shechts another Korban as a Pesach.

Answer #1: The Ri explains, that there are many occasions, one could retort 've'li'Ta'amech' (According to you it is still a Kashya!', but doesn't).

Answer #2: Moreover, it is not comparable to the case of the two babies - since there, he is certainly Chayav when he circumcises the Sunday baby on Shabbos, because neither did he perform a Mitzvah nor does Shabbos stand to be overridden on account of the second baby ...

Answer #2 (cont.): As opposed to the case of Pesach, where he changed to something that is permitted, where he is Patur, since Shabbos does stand to be overridden by that Pesach, if he would Shecht it li'Shemo.

Question: The Rashba asks why Rebbi Yehoshua asks on Rebbi Eliezer 'Say by Shelamim which he changed to something that is permitted'?

Question (cont.): Since Rebbi Eliezer does not differentiate between someone who uproots (Oker) and someone who errs (To'eh), how will the fact that he changed to something that is permitted make any difference?

Question (cont.): Seeing as, according to Rebbi Yehoshua Oker to something that is permitted renders one Chayav? If so, the same will apply to To'eh according to Rebbi Eliezer?

Answer: What Rebbi Yehoshua is saying to Rebbi Eliezer is as follows: 'Granted that you do not differentiate between Oker and To'eh; nevertheless, there is reason to differentiate - since in the Reisha, there are two disadvantages, 1. Oker; 2. To something that is Asur; whereas, in the Seifa, there are two advantages; 1. To'eh; 2. To something that is permitted.

Implied Question: He could have differentiated in that itself, between where he circumcised it first and the other, where he did not.

Answer: Only he mentions a Chidush in the Seifa, where he circumcised the Sunday baby on Shabbos, where he is Patur, even though he did not perform a Mitzvah, seeing as Shabbos stands to be overridden.

Answer (cont.): In fact there is a Chidush in the Reisha too, where it mentions Erev Shabbos, and where he is Chayav, even though he performed a Mitzvah, seeing as Shabbos does not stand to be overridden.

Clarification: The Gemara will also ask shortly that there is the Simchah of Onah (intimacy)

Question: But we are talking about one's wife who is a Nidah, where there is no Mitzvah, and no Simchas Onah?

Answer: The Ri explains that the Gemara is asking according to latter Lashon, which exempts someone who errs in a D'var Mitzvah, even if he did not perform a Mitzvah. Hence it asks that since there is Simchah, it is considered 'Ta'ah bi'D'evar Mitzvah?

Answer (cont.): And the Gemara answers - that he (is Chayav because he) ought to have asked a She'eilah and presents an alternative one).

Refuted Explanation: We cannot explain that it speaks where he knows that it is close to her period, and that he not sure whether she is really a Nidah or not ...

Refutation: Because why is he then Patur in the case of his Yevamah, seeing as he knows that she is close to her period - which involves an Isur d'Oraysa, which we learn from the Pasuk "ve'Hizartem es B'nei Yisrael".

Explanation: It must therefore be speaking where he does not know whether she is close to her period or not, in which case he ought to have asked her.

Implied Question: And when the Gemara says in the second Perek of Nidah (Daf 15.) that 'All women have a Chezkas Taharah to their husbands' ...

Answer: It speaks specifically where he knows that she is not close to her period, in which case we do not suspect that she may have changed her period.

Implied Question: In fact, the Gemara could just as well have said that he does not know whether she is actually a Nidah or not ...

Answer: But it opted to mention a case even where he knows that she is not, yet since he has doubts as to whether she is close to her period, in the case of a wife, he is nevertheless Chayav.

Alternative Explanation: The Gemara could however, have referred to a case where he is not certain whether she is actually a Nidah or not, to teach us that nevertheless, he is Patur in the case of a Yevamah.