SHOGEG IS CONSIDERED A TRANSGRESSION [Shogeg]
According to R. Yishmael, the outer goat atones for one who did not know at the beginning, nor at the end.
Bechoros 37a (Mishnah): If Reuven slaughtered a cow (and sold it to Shimon), then it became known that it is a Tereifah, what was eaten was eaten, Shimon returns the meat that was not eaten, Reuven returns the money.
Kidushin 42b - Question: Why does a Beraisa teach that if Reuven's Shali'ach bought something with Hekdesh money, Reuven transgressed Me'ilah? We should say that the Shelichus is invalid!
Rambam (Hilchos Shegagos 5:6): If a couple had relations not at the time of her Veses (when she expects to become Nidah) and she became Nidah, they are exempt from a Korban. This is like Ones, not Shogeg. Shogeg is one who should have checked and been careful, and because he was not careful before acting, he came to err. Here, he did nothing wrong.
Rambam (Hilchos Isurei Bi'ah 1:12): If one had Bi'ah with Ervah (a woman forbidden to him with Kares) k'Mis'asek (he did not intend for the action), even though he did not intend, he is liable. The same applies to Chayvei Lavin and Sheniyos (Arayos mid'Rabanan).
Rebuttal (Ra'avad): What liability for a Korban applies (to Chayvei Lavin and Sheniyos)?!
Kesef Mishneh: The Magid Mishneh said that this must be a printing mistake in the Rambam. I say that the Rambam means that even though he is not lashed, he is liable to Shamayim like one who transgressed.
Rambam (Hilchos Ma'achalos Asuros 14:12): If one ate an Asur food in jest or Mis'asek, even if he did not intend to eat, since he benefited, he is liable only one who intended to eat.
Tosfos (Shevuos 19a DH Harei): R. Tam says that Helam Mikdash exempts from Oleh v'Yored (i.e. a rich person brings an animal, a poor person brings birds, and a very poor person brings a Minchah flour offering), but he is liable to bring Chatas Kavu'a (it must be an animal). We learn from Avodah Zarah that whenever one is Chayav Kares b'Mezid, he brings Chatas for Shogeg. We said (2a) that the inner goat atones for Aveiros of Tum'as Mikdash in which there was no Yedi'ah (knowledge) at the beginning. This connotes that there is no Chatas for it, for if there were, the goat would not atone for it! There, surely it atones totally, for we should not be more stringent when there was Yedi'ah only at the end than when there was Yedi'ah at the beginning and at the end. However, 'exempt' connotes totally exempt. Also, the Gemara found Chatas Kavu'a for Tum'as Mikdash only regarding a Nasi (24b). Rather, he is totally exempt.This was a matter that was in a general rule (Chatas Kavu'a), and left for a Chidush (Oleh v'Yored), and it does not return to the rule even when there is no Oleh v'Yored.
Tosfos (Kidushin 42b DH Amai): Why did the Gemara ask why the Meshale'ach is Mo'el through his Shali'ach? Surely we discuss Shogeg, for there is no Me'ilah b'Mezid. If so, there is Shali'ach l'Devar Aveirah, for we cannot say 'you should listen to the Rav (Hash-m), and not the Talmid!' The Ri says that we ask why the Meshale'ach is liable even if the Shali'ach was Mezid.
Nesivos ha'Mishpat (348:4): I say that since one who was Shogeg must bring a Kaparah for Me'ilah, he is considered liable, for he should have checked. Therefore, it is more appropriate to say that the Shali'ach was Mo'el, since he did the action. Because 'you should listen to the Rav...', he should have checked better. We find that a woman who remarried based on one witness that her husband died must bring a Korban (if he was really alive). Yo'av should not have relied on David to cause Uriyah's death, just like Sha'ul's servants did not rely on Sha'ul.
Ohr Some'ach (Hilchos Gerushin 1:1): R. Gershom's Cherem not to divorce Bal Korchah (against her will) applies also to the witnesses and scribe. If they knew that he divorces Bal Korchah, they are Pasul and the Get is Pasul. If they were Shogeg, perhaps their Shlichus is Batel, for had they known, they would not have signed. However, if the Cherem is mid'Rabanan, like Acharonim wrote, perhaps Shogeg about a mid'Rabanan is not an Aveirah at all. Isurim mid'Rabanan are not intrinsically forbidden. One must guard them due to Lo Sasur. If one was Shogeg, his transgression was not due to disobeying Chachamim, rather, because he did not know, and this is not an Aveirah at all. If one bought Isur, and found out that it was Asur only after he ate it, it is a Mekach Ta'os (mistaken sale) and he gets back his money. He does not deduct for what he ate. The Rambam connotes like the Shach, that if it was Asur mid'Rabanan, he deducts the full value. This is because eating an Isur mid'Rabanan is not considered an Isur at all, like the Nesivos ha'Mishpat explained. However, if so one may give an Isur mid'Rabanan to another if the other does not know! Surely one may not say so! Rav said 'Shmuel would not stumble by giving to me something that I forbid (even mid'Rabanan)' (Chulin 111b). The Rambam says that if one had Bi'ah with Sheniyos k'Mis'asek (he did not intend for the act), he is liable, i.e. to Shamayim (Kesef Mishneh), and he needs a Kaparah. Do not say that Mis'asek with Arayos is different because he benefited, for the Rambam said similarly about eating.
Note: Mis'asek with Chelev and Arayos is liable because he benefited! (Krisos 19a) The Radvaz and Kesef Mishneh (Hilchos Ma'achalos Asuros 14:12) say that the Rambam applies this to all forbidden food. It seems that the Ohr Some'ach disagrees.
Ohr Some'ach: This disproves R. Akiva Eiger, who said that Mis'asek transgressed and needs Kaparah. It also proves that one who transgressed a mid'Rabanan law b'Shogeg needs Kaparah. We can say that Mis'asek b'Chelev or Arayos, since he benefits, brings a Korban like one who was Shogeg. However, if Shogeg in a mid'Rabanan is not an Aveirah, Hana'ah is no reason to consider it like Mezid! Therefore, the Get is Pasul.
Nesivos ha'Mishpat (Bi'urim 28:8): The Ketzos ha'Choshen (8) says that if one swore 'I do not know testimony for you', and witnesses testified that he saw testimony, he is not disqualified from swearing, for perhaps he did not know. Often, one swears 'I do not know', and he is not disqualified. We do not say that presumably, he knew. However, if he swore 'I never knew testimony for you', and witnesses testified that he saw and knew testimony, he is disqualified from swearing. He is not believed to say that he forgot. Tosfos (Shevuos 37a DH Hezid) says that we can never know if witnesses transgressed Shevu'as ha'Edus b'Mezid, for perhaps they forgot. He refers to Stam Shevu'as ha'Edus, i.e. I do not know (now). However, if he swore 'I did not know', he must pay arouse himself to remember, for man is always Mu'ad, and even Shogeg requires Kaparah.
Mesovev Nesivos (8): This is not relevant to Shogeg requires Kaparah. He is not believed even if he says that he was Ones or Mut'eh (tricked), even though he needs no Kaparah. Rather, one who sins in front of us is not believed to claim Shogeg, Ones or Mut'eh
Eliyahu Rabah (524:13): The Shlah was astounded. Sukos is called the first day for the calculation of Aveiros (Tanchuma on Vayikra 23:40), for Stam one does not sin between Yom Kipur and Sukos, for he is busy with Sukah and Lulav, but surely if one sins, they are counted! Perhaps one who sins b'Shogeg does not need Kaparah during these days, for he is busy with Mitzvos.
Aruch ha'Shulchan (568:3): If one ate b'Mezid on a fast day, he should fast another day to atone for this. He need not do so if he was Shogeg.
Aruch ha'Shulchan (602:7): Shogeg comes from a lack of carefulness. Ones is different. No Teshuvah is required for Ones.
Igros Moshe (1:175): If one realized that he had Bi'ah with his wife b'Isur, he should tell her, so (also) she will repent. We find that one who never realized that he transgressed Tum'as Mikdash needs Kaparah even if he will never find out. Clearly, the same applies to all Mitzvos.