Mishnah nine, the last of the chapter, brings four testimonies transmitted - according to the version of the Mishnah before us - by Rabbi Nechunya ben HaKadmon. These testimonies appear in Maseches Eduyos as well, and there the version reads Rabbi Yochanan ben HaKadmon, which is apparently the correct version. Two of the items deal with marriage and divorce, and two others with the laws of theft.
The first case - a deaf-mute girl whose father married her off:
Kiddushin, the first stage of marriage, is an act of acquisition: the woman transfers her marital rights in exchange for the ring. For this reason she must be a legal personality possessing da'as - the legal standard by which a person understands the consequences of his actions. One who lacks da'as cannot effect legal transactions, kiddushin among them.
Even so, there can be a situation in which a girl who lacks da'as is married by Torah law, since while she is a minor or a na'arah - up to the age of twelve and a half - her father acts on her behalf. Take, for example, an eleven year old girl who is a deaf-mute, who neither hears nor speaks: such a person is considered to lack da'as and cannot carry out acquisitions, yet her father accepts her kiddushin on her behalf, and she is therefore married by Torah law even though she has no da'as at all.
Divorce, by contrast, is effected by handing the get from the husband's hand into his wife's hand (or its equivalent), and it does not require her da'as. It is enough that she receive the get and understand that it means separation and that she is not to return to him - unlike an animal, which cannot grasp the meaning of being sent away and keeps coming back. As long as she has that much comprehension, even though she lacks da'as in the legal sense, she is fit to be divorced.
From here the Mishnah establishes that a deaf-mute girl who was betrothed through her father and is married by Torah law can be divorced with an ordinary get that her husband gives her, since she has enough comprehension to understand that her husband is separating from her and that she is not to return. The get handed to her therefore severs a marriage that exists on the Torah level.
In the words of the Mishnah: "He'id Rabbi Nechunya ben Gudgeda al hachereshes shehisi'ah aviha - shehi yotz'ah b'get" - a deaf-mute woman who is married to her husband on the Torah level by virtue of her father's acceptance of her kiddushin goes out and is divorced through the handing over of a get, just like any other woman. Of course, if she lacks even the comprehension to understand that she is not to return, and she keeps coming back again and again, the divorce does not take effect, but that is not because of her being a deaf-mute as such.
The second case - a minor girl who married a kohen:
The background to this law: only a kohen may eat Terumah, and anyone considered an outsider is forbidden to eat it. Once a woman marries a kohen she becomes part of his household, and just as the members of his household - his children and even his slaves - eat Terumah by virtue of him, so does she.
The novelty of the Mishnah concerns a woman whose marriage is rabbinic only, meaning that by Torah law she is not married: even so, she is permitted to eat rabbinic Terumah in her husband's home. Terumah of Torah status is forbidden to her by Torah law, but we do not suspect that she will come, through this, to eat Terumah of Torah status as well and transgress the prohibition.
How does a minor girl become married by rabbinic law? When her father has died and she is left an orphan, and she is not old enough to accept kiddushin herself - still a minor, under the age of twelve - the Sages granted authority to her mother or to her brother who has reached the age of mitzvos to marry her off and to accept her kiddushin on her behalf. This enactment was made for her benefit, and if in time she finds that they matched her with a young man who is not fitting, she can perform mi'un and reject the marriage.
The Mishnah further adds that if this minor girl dies during her husband's lifetime, her husband inherits her. True, a husband generally inherits his wife (and simply understood this inheritance is of Torah status, though there is an opinion that it is rabbinic), but here the marriage itself is only rabbinic, and by Torah law her property would belong to her heirs - her brother, say - and not to her husband. How, then, do the Sages have the power to transfer it to the husband? The answer is by virtue of the principle 'hefker beis din hefker': a court is authorized to declare any property ownerless and to grant it to whomever it wishes. The Sages declared her property ownerless, and on that basis it passes to her husband.
In the words of the Mishnah: "V'al ketanah bas Yisrael shenisses l'kohen - shehi ocheles biTerumah, v'im meisah - ba'alah yorshah" - a minor girl under the age of twelve whose father is not a kohen, and who was married off to a kohen by her mother on the rabbinic level, may eat the Terumah she receives from her husband (rabbinic Terumah only), and if she dies in his lifetime, her husband inherits her.
The third case - the stolen beam and takanas hashavim:
The third case concerns takanas hashavim - a rabbinic enactment designed to make repentance easier. The Torah says: "and he shall return the stolen object that he stole," meaning that the thief must return the very item he took. The implication is that as long as the stolen object still exists as it was, the thief is obligated to return it itself; but if he sold it, or it broke, or it changed and became something entirely new, he does not return the object but only its value. So, for example, one who steals a piece of wood and fashions it into a boat does not return the boat, since it is now a boat and not a piece of wood, but rather pays the value of the wood he stole.
And what is the law when the beam remains exactly as it was, but the thief built it into his house and set it in place as one of the ceiling beams? To return the beam itself he would have to dismantle the entire house and take it down - an enormous expense that would discourage him from repenting altogether. For this reason the Sages instituted takanas hashavim: even though by strict law the beam still exists and could be returned intact, since returning it involves a significant loss, he need not return the beam itself but only its value - all so that it should be easy for a person to repent.
In the words of the Mishnah: "V'al hamerish hagazul sheb'nao b'birah - sheyitein es damav" - a stolen beam that was set in place as a ceiling beam in a person's building: we do not obligate him to dismantle the entire house in order to extract it and return it to its owner; rather he pays its value, and thus the matter is settled to everyone's benefit.
The fourth case - a stolen sin offering and the proper functioning of the altar:
The final case deals with a stolen animal that the thief consecrated and offered as a sin offering. The procedure is that one who brings a sin offering hands the animal over to the kohen, and the kohen eats it after it is offered. A disqualified offering may not be slaughtered in the Azarah, and certainly may not be eaten. The concern was that if the kohanim would suspect that the man had stolen the animal he handed them for his sin offering, they would refrain from performing their service and from eating meat that in their view was disqualified.
Therefore the Sages said: if a person stole an animal and offered it as his sin offering, there is no need to be concerned; the atonement is effective for him and he need not bring another. As a result, the kohanim will know that the matter is entirely in order, and they will perform their service properly.
But what is going on behind the scenes? After all, the thief is not the owner of the animal, and seemingly he has no power to consecrate it and bring it as a sin offering for himself. In the commentaries we find two approaches (and the language of the Bartenura here is ambiguous):
In truth the offering does not count for him, and by strict law he is obligated to bring another sin offering. However, the Sages, by virtue of their authority to enact and to uproot a Torah law passively, told him not to bring a second one, and in this way the kohanim are put at ease.
The offering genuinely counts for him; it is a legitimate, valid sin offering, and the kohanim's eating of it is entirely permitted. This explanation is based on the Mishnah's wording "shehi mechaperes," and it is the view of the Rashbam and others. The mechanism for this is hefker beis din hefker: the court declares the stolen animal ownerless, and consequently, when the thief consecrates it, the sanctity of his sin offering takes effect upon it, and the offering is valid.
And even though it is clear that the man is a thief and that his act is disgraceful, and the Holy One, blessed is He, takes no pleasure at all in this process but is repulsed by it, the enactment nevertheless removes the stumbling block from before the kohanim, so that they do not hesitate to offer people's sin offerings and eat them, and the Beis HaMikdash functions as it is meant to function.
Two qualifications: all of this applies to an animal that was stolen in secret, but if the matter became publicly known - three people or more know that the animal is stolen - the enactment is of no help at all. Furthermore, this applies specifically to a sin offering, which is eaten by the kohanim; but a burnt offering, which is entirely consumed on the altar and of which the kohanim eat nothing, was not included in the enactment, and it would never occur to anyone to say that a stolen burnt offering that was brought is effective. A sin offering is different, because with it there is a concern that the kohanim will refrain from their service out of suspicion of the person, and a serious problem will arise.
This is the concept of tikkun hamizbe'ach, the proper functioning of the Altar: the Sages institute enactments when there is a choice between two evils, and they choose the lesser of the two. Their choice here is that the Beis HaMikdash should function properly, without the kohanim suspecting that an object is stolen and refusing to perform their service.
In the words of the Mishnah: "V'al hachatas hagezulah shelo nod'ah larabim - shehi mechaperes, mipnei tikkun hamizbe'ach" - a stolen sin offering whose theft did not become publicly known, meaning that fewer than three people knew about it, atones and is effective. Either it is genuinely effective, following the principle of 'hefker beis din hefker' (the court has the power to declare property ownerless); or it is not truly effective, but we relate to it as though it were, so that the owner need not bring a second offering, and we tell the kohanim that everything is in order so that they will not be concerned. "Mipnei tikkun hamizbe'ach" - literally, for the repair of the Altar, meaning that the Altar should function properly and the kohanim should take part in their service without hesitation, even with the offerings of people they do not trust.
In summary: In this Mishnah we learned the four testimonies: a deaf-mute woman whose father married her off, so that she is married by Torah law - she is released with a get, since divorce does not require full mental capacity but only basic understanding; a minor girl who was married to a kohen by rabbinic law - she eats Terumah of rabbinic origin, and if she dies her husband inherits her by force of 'hefker beis din hefker'; a stolen beam that was built into a building - the thief pays its value because of takanas hashavim, the enactment for the benefit of penitents; and a stolen sin offering whose theft did not become publicly known - it atones because of tikkun hamizbe'ach.