Explanation: The Gemara implies that even though he found out in the middle that he is having relations with a Nidah, being that he did not know that he is liable to bring a Chatas because he thinks he is a victim of forced circumstances, he is considered to have only one lapse of knowledge. This is also how Rashi explains the Gemara.

Question: In Shabbos (71a), Rebbi Yirmiyah asks Rebbi Zeira what the law would be if a person harvested and ground an amount equal to half a fig while forgetting it was Shabbos, but knowing that this action would be forbidden on Shabbos, and he then ground another half fig with the opposite mindset? (He knows it is Shabbos, but forgets this is forbidden.) Do these two amounts of half of a fig combine to make him bring a Korban? Rebbi Zeira answered that they are separate regarding having to bring a Korban, and do not combine. This means that if each time he would have harvested and ground a size of a fig he would indeed be liable for two Korbanos Chatas, even though he did not realize that he had done anything wrong in between the two actions. (In this case he also did not realize he did anything wrong, yet he must bring two Chataos. How is this different from our Gemara where he only must bring one?)

Answer #1: It is possible to answer that Rava is basing himself on his opinion there that he is only liable for one Chatas in such a case (unlike Rebbi Zeira).

Answer #2: Alternatively, in Shabbos this is considered knowing, being that he now knows whatever had previously been in doubt at the time he transgressed Shabbos. (In other words, after everything is done on Shabbos, he realizes that the entire time he had not acted properly, and would have done things differently. However, he would not have refrained from having relations in that same situation a different time, as he does not know it is forbidden to have such relations close to the time when a woman will be a Nidah.)

Observation: The Gemara also could have said the case is when it is near her period and it is referring to pulling away.

Question: This is difficult. The Gemara could have asked a better question from the second part of the Mishnah (Nidah 14a) which states that if blood was found on her cloth, they are doubtfully impure and exempt from a Korban. Why is he exempt from bringing a Korban (if it is referring to him pulling away) if she said that she became impure?

Observation: The Mishnah in Nidah (14a) states that if blood is found on her cloth immediately after relations they are liable to bring a Korban. The Gemara (14b) explains that this is the amount of time in which the member leaves and the cloth immediately enters.

This must be referring to a case where the person's member was hard when pulling away. If it was soft, this is not deemed checking immediately. [Waiting to soften is an interruption between the checking and the supposed transgression. This interruption means that he would not be liable to bring a Korban.]

Explanation: Whatever Rava is deducing from the Mishnah can be deduced from the Pasuk. This is as we derive later (18b) that a warning prohibiting someone who is having relations with a woman who suddenly says she has become impure from continuing is found in the Pasuk, "And to a woman in the impurity of Nidah do not come close." (Tosfos seemingly means, "And her Nidah is on her," as stated by the Tosfos Ha'Rosh.) This also implies that one should not pull away. This teaches us that one is not liable for having relations while dead (i.e. soft), as being that he was commanded not to pull away he is supposed to wait until his member becomes soft.

Question: This is difficult. In Yevamos (55b), Rava understands from the words, "Shichvas Zera" -- "semen" stated by the prohibition against having relations with a married woman that if one has relations while soft he is exempt. (This is because the prohibition is specifically when he is in a state when he can emit semen. Which Pasuk is this derived from, the one quoted above from our Gemara or the one quoted in Yevamos?)

Opinion #1: Some commentaries say that this "if so" means if we hold like Rav Huna who says one must dig his fingernails into the ground etc.

Question: This is difficult. Rabah bar Chanan should be asking regarding the Mishnah, as the Mishnah implies that it is possible to fix the situation if he did not separate immediately! (The Mishnah says that if he pulls away immediately he is liable, implying that as long as he does not do so immediately he may not have to bring a Chatas!)

Opinion #2: Rather, it is possible to explains that the question is on Abaye. It is understandable if one is exempt if he is soft when he pulls away, as it is no longer possible to say "long" (waiting) and "short" (not waiting), being that there is no prohibition of having relations with a Nidah regarding either one (as long as he is soft). This is unlike Tumas Mikdash, as Tumas Mikdash is present whether one waits or not.

This is why the Mishnah did not mention "long" and "short" regarding Nidah like it did regarding the Mikdash, as the exemption regarding Nidah is not because the relations are short, but rather because it is deemed that there are no further relations.

Rather, according to Abaye who says that he is liable, and it is considered having relations when one pulls away when soft, the Mishnah should have stated the following difference. "Taking a long time to pull away," meaning doing so with great pleasure, makes one liable. "Taking a short time to pull away," meaning doing so with little pleasure, makes one exempt. We would not mistakenly think that being soft makes one exempt, as we are leaving aside the exact terms used in the Mishnah regarding the Mikdash ("long" and "short").

The Gemara answers that this difference would not be understood well, being that the term "long" used regarding Mikdash is actually similar to the term "short" used regarding Nidah (as both mean that he waits longer until he leaves).

Question: Perhaps it should say the opposite, that if he takes a short time (pulls out immediately) he is liable, but if he takes a long time he is exempt?

Answer #1: Being that the Mishnah cannot use the same terminology as by the Mikdash, it abandons this terminology entirely.

Answer #2: Additionally, if it would say this, it would not be implying the reason for the exemption and the liability. On the contrary, "long" implies more reason for liability and "short" implies less reason for liability.

Explanation: Rashi explains that if the case is when it is close to her period, being that having relations while soft makes one liable, so too withdrawing while soft makes one liable. Rashi implies that he would be liable for two Korbanos, even if he withdrew while soft. Accordingly, even though he is liable for entering he is also liable for exiting.

This is also how Rashi explains the Gemara later. When the Gemara says that Abaye said his statement in general, Rashi explains that he was not addressing another statement. He merely said that if someone is having relations with a woman when she is close to getting her period, mistakenly thinking he could have relations with her before her period arrived, if she tells him in the middle that she received her period he is liable for two sins. It does not make a difference (Rashi according to Abaye) if he withdrew when hard or soft.

It seems like this is indeed his opinion. Being that he had relations with her close to the arrival of her period, he originally is considered to have accidentally done two sins, namely entering and withdrawing. When she says that she became impure, there is knowledge between accidentally going in and accidentally going out. Going out is considered accidental, even though he knows when he withdraws that he is having relations with a Nidah, being that this happened because he entered when he should not have done so.

Question: This is difficult. The Gemara earlier implies that the only time a person is liable for two sins is if he is a Talmid Chacham (i.e. he knows about the prohibition) for one and not the other. According to this opinion, however, the case could be where he is a Talmid Chacham for both, and he withdrew when soft.

Answer: It is possible to answer that the only reason that the Gemara earlier established the case as involving a Talmid Chacham for one and not the other is because it held that having relations when soft exempts one from a Korban. The only time he is liable to bring two Korbanos is when he withdrew immediately.

Implied Question: Rashi here mentions that the case is when one is a Talmid Chacham for one and not the other. (Didn't we just say that this does not have to be the case according to Abaye?)

Answer: He explained this because of the case of one who withdraws when hard.

Question: However, there is a difficulty. In Shabbos (102a), the Mishnah states, "The rule is that all obligations to bring a Chatas are only if the beginning and conclusion were by accident." It is apparent there that if a person threw a stone, and only realized after it left his hand that it was Shabbos, he is exempt from bringing a Korban. This is despite the fact that when it originally left his hand he did not know that it was Shabbos, and he was powerless to return the stone (as he had thrown it). (How, then, can one be liable for withdrawing, when he knew before he entered that this is forbidden according to Torah law if she indeed becomes a Nidah?)

Answer: Our Gemara deduces that if Abaye calls him an "Anus" -- "victim of forced circumstances," the case must be when she is not expecting her period. If she was expecting her period it is not possible to call him an Anus, as he was negligent by entering in the first place. The only reason he is exempt is because there is one accidental sin, as both entering and withdrawing are do to his accidental entering.

Question: Who pressed Abaye to establish the Mishnah as being a case where she was not expecting her period, and to say that he is totally exempt if he withdrew while soft? Why don't we say that it is when she is expecting her period, and when the Mishnah says he is exempt it means he is exempt from bringing a Korban due to his withdrawal?

Answer: It is possible to answer that the terminology of the Mishnah implies that he is totally exempt if he did not immediately withdraw.

Explanation: The derivation is from the word, "Alav" -- "on him." However, from the word, "va'Tehi" one cannot derive, as it is needed for the teaching stated in Yevamos (49b) that a person can effectively be Mekadesh a woman even when she is a Nidah.

Explanation: The Gemara asks about a Lav because one cannot be liable to bring a Chatas unless there is a Lav, just as accidentally transgressing Pesach and Milah do not make one liable to bring a Chatas (even though they are punishable when done on purpose with Kares).