In Mishnah 3 of chapter 2, the Mishnah continues to explain that the rules governing the court closely parallel the rules stated regarding the anointed Kohen. A ruling of the court obligates a sacrifice only under two conditions: that the ruling was mistaken, and that the people transgressed the Torah unintentionally on the strength of that mistaken ruling.
The same applies to the anointed Kohen, the anointed Kohen Gadol discussed in the previous Mishnah: if he issued a ruling for himself and acted according to his mistaken ruling, he brings his own special bull. So too with the sin of idolatry - neither the court nor the anointed Kohen becomes liable for their special sacrifice unless there was a mistaken ruling and the transgression was committed unintentionally.
The scope of the transgressions covered by the bull for a forgotten ruling:
The bull for a forgotten ruling is brought, and likewise the sacrifice of the anointed Kohen is brought, only for transgressions whose "zedonan kareis ve'shigegasan chatas" - that is, one who commits them deliberately, knowing that they are forbidden, is liable to kareis; and one who commits them unintentionally, without intending to transgress, brings a fixed sin offering. The identical rule applies to the anointed Kohen: it must be the type of transgression for which an ordinary person would be liable to kareis when deliberate and to a fixed sin offering when unintentional.
What are these transgressions? The Rambam opens by writing that there are forty-three transgressions for which a sin offering is brought, whereas the first Mishnah in tractate Kerisos lists thirty-six transgressions whose punishment is kareis. How do we reconcile the two lists?
The thirty-six kareis transgressions in the Mishnah in Kerisos:
Forbidden relations - fifteen.
The blasphemer - one who curses and reviles the Name.
Idolatry - three: actual idol worship, passing a child through fire to Molech, and the practice of ov.
Desecrating Shabbos - performing labor on Shabbos.
Tumah - two: entering the Beis HaMikdash while in a state of tumah, and eating sacrificial food while in a state of tumah.
Forbidden foods - four: blood; cheilev, the forbidden fat; piggul - sacrificial meat which, during one of the four essential services of offering the sacrifice, the kohen intended to burn or eat outside its designated time; and nosar - sacrificial meat left over past the final time allotted for that sacrifice.
Service outside the Beis HaMikdash - two: slaughtering sacrificial animals outside the Beis HaMikdash where they must be offered, and offering them up outside.
Eating chametz on Pesach.
Yom Kippur - two: eating on Yom Kippur and performing labor on it.
The anointing oil and the incense - three: making the anointing oil, making the incense according to its formula, and anointing oneself with the anointing oil.
Positive commandments - two: circumcision and participation in the Pesach offering. One who deliberately fails to fulfill them is liable to kareis. (The details of when exactly the liability to kareis takes effect for one who was not circumcised are complex, and this is not the place for them.)
The point of our Mishnah is that not all of those thirty-six are transgressions for which a bull for a forgotten ruling is brought, or for which the anointed Kohen brings his special sacrifice. Five of them, though their deliberate violation carries kareis, do not carry a fixed sin offering when committed unintentionally:
The blasphemer - one who curses the Name, since the matter consists of speech, and a sin offering is not brought for something that involves no action, no physical deed.
Eating sacrificial food while in a state of tumah and entering the Beis HaMikdash while in a state of tumah - even though their deliberate violation carries kareis, one who commits them unintentionally does not bring a fixed sin offering but rather an adjustable offering, which varies according to his means: an ordinary sin offering, a female goat or lamb, for one who can afford it; and for one who cannot afford it - two birds, or even a sinner's meal offering of flour alone.
Failing to perform circumcision and failing to participate in the Pesach offering - these are positive commandments, and not fulfilling them is not an action but the absence of an action; therefore no sin offering is brought for them, even though one who deliberately fails to fulfill them is liable to kareis.
These, then, are five transgressions whose deliberate violation carries kareis but whose unintentional violation carries not a fixed sin offering but something else, leaving thirty-one transgressions - and these are the ones our Mishnah is discussing.
The Rambam's count - forty-three:
The Rambam counts forty-three, because he itemizes more acts in the area of forbidden relations: instead of fifteen forbidden relations he counts twenty-six, an addition of eleven. The reason is this: sometimes a single prohibition includes several forbidden women. For example, the prohibition against relations with a woman and her daughter - one who is married to a woman is forbidden both to his wife's mother and to his wife's daughter, and both are included in that very same prohibition, and it extends further to grandmothers and the like. So even though it is a single commandment, several women are in fact forbidden through it. There is a further addition: the Rambam counts not only ov but also yidoni, two distinct categories of divination practices. And in this way the count reaches forty-three.
Avodah zarah - the exception:
Avodah zarah, which we mentioned, has a different law, and in practice only forty-two of the forty-three are identical in their law. One who serves avodah zarah becomes liable to kares and to a chatas in two ways: if he served it with one of the four services with which Hashem is served - bowing, slaughtering, burning incense and pouring a libation - or if he served it in its own particular manner of worship. The difference is that the chatas brought for it is not the ordinary chatas: an ordinary person brings for it only a she-goat in its first year, and for that reason its law is different.
The same applies when the Sanhedrin issued such a ruling: instead of the bull, they bring a goat as a chatas and a bull as an olah, as was explained above. And in such a case, according to a halachah cited in the name of the Chasam Sofer, even the anointed kohen brings that special she-goat in its first year. And remember: under ordinary circumstances the Kohen Gadol, the anointed kohen, never brings a chatas; this, then, is the exception - for avodah zarah he brings that very she-goat in its first year that an ordinary person brings, provided that he ruled in error and acted according to his mistaken ruling.
In summary: In this section we learned that the law of the beis din and the law of the anointed kohen share the same conditions - a mistaken ruling and an inadvertent act that follows from it; and that the par he'elem davar is brought only for transgressions whose intentional violation carries kares and whose inadvertent violation requires a fixed chatas. We counted the thirty-six kares penalties listed in the Mishnah in Kereisos, subtracted from them the five whose inadvertent violation does not require a fixed chatas and were left with thirty-one, examined the Rambam's count - forty-three - and noted the exceptional law of avodah zarah with regard to its offerings.