1) "KA'SAVUR HAYISI"
QUESTION: The Mishnah states that when a man is Mekadesh a woman and then claims, "I thought she was a Kohenes, but she is actually a Leviyah," the Kidushin is valid because she did not mislead him in any way. The Mishnah then states that when a man is Mekadesh a woman with a condition such as, "You are hereby Mekudeshes to me from after I convert," the Kidushin is not valid.
The previous Mishnah (61a) discusses the Halachos of a statement made with a Tenai (condition). The Mishnah here and the following Mishnah discuss different types of conditions and when they take effect. Accordingly, the first Halachah of the Mishnah here, "ka'Savur Hayisi," seems out of place. Since the subject of this case is not the Tenai that was stipulated but the intention of the man who was Mekadesh the woman, it should have been included in the Mishnah earlier (50a-51b) which discusses the intention of the Mekadesh. Why is it included in the Mishnah here?
ANSWER: The RAN explains that in certain cases even Rebbi Meir agrees that an explicit "Tenai Kaful" is not necessary. When the intention of the person who performs the act is clear to all, Rebbi Meir's requirements are not necessary (see also 49b, TOSFOS DH Devarim). This Mishnah teaches that "ka'Savur Hayisi" is not such a case; it is not assumed that the intention of the Mekadesh was to marry specifically a Kohenes or an Ashirah. Rather, the Kidushin takes effect even if the woman is not a Kohenes or Ashirah. If the Mekadesh would have intended to make the Kidushin contingent upon those factors, he would have been required to make a statement of Tenai with all of the requirements of Tenai.

62b----------------------------------------62b

2) WHEN DOES "B'YADO" APPLY?
QUESTION: The Gemara teaches that any action which is within a person's ability to do ("b'Yado" -- "in his hands") is considered as though it has been done. Rebbi Aba bar Mamal questions this principle from the case of a master who is Mekadesh his Shifchah Kena'anis for after frees her, in which case the Kidushin does not take effect immediately. According to the principle of "b'Yado," she should become Mekudeshes to him immediately since it is within his ability to free her. The Gemara answers that the case of a Shifchah Kena'anis differs from an ordinary case of "b'Yado," because before the Shifchah is freed her status is like that of a Behemah, and after she is freed she has the status of "Da'as Acheres," an independent mind.
The Gemara, however, does not retract its initial understanding of the case of one who frees his Eved or Shifchah. The release of the Shifchah is considered "in the hands of" the master and does not depend on anyone or anything else (in contrast to the case of conversion, which is not in the person's hands because it depends on three others agreeing to witness his conversion). The only difference is the change of status which occurs to the woman -- her change from the status of a "Behemah" to the status of one who has Da'as. Why should that change affect the logic of "b'Yado"?
ANSWER: The Acharonim explain that when the logic of "b'Yado" applies, the action which is "b'Yado" is considered to have been performed already. Since all of the circumstances necessary to perform the action are present, and the person easily can perform the action, it is considered as already done. (See TOSFOS RI HA'ZAKEN in the following Sugya of "l'Achar she'Agarshech" who states clearly that "b'Yado" is considered "as if it was already done.")
This does not mean that the act is considered to have been done in reality (b'Metzi'us). The status of Terumah cannot take effect on fruits when all of the fruits are still mixed together, even though it is in the owner's hands to separate the fruits. Similarly, Kidushin cannot take effect when the Mekadesh is still a Nochri, even though it is in his hands to convert. The desired effect cannot take place until the act has actually been done. Nevertheless, the logic of "b'Yado" enables the act to be viewed as through it was done with regard to other conditions which are dependent on that act (that is, when the act is a condition for something else, the act may be viewed as having been done already and thus the condition as having been fulfilled, so that the other act can take effect).
According to this understanding of the concept of "b'Yado," it is clear that certain actions (for which the "b'Yado" act is a condition) are so far removed and non-existent at the time of the "b'Yado" act that "b'Yado" does not enable the condition to be considered as having been fulfilled. The state of a woman who is a Shifchah is far removed from the state of a woman who is free. A Shifchah is compared to a Behemah, while a free woman is "Da'as Acheres." In her present state, the Shifchah has no element of freedom (or anything associated with freedom). The principle of "b'Yado" serves only to resolve technical problems which make the act one that is "Eino ba'Olam" or "Mechusar Ma'aseh." When, however, there is an intrinsic lack of existence of the act (that is, it is not an act that is somewhat existent and which is merely "Mechusar Ma'aseh," but it is completely "Eino ba'Olam"), "b'Yado" cannot create something ("Yesh me'Ayin") which does not exist.
3) "YOU ARE HEREBY MEKUDESHES TO ME FOR AFTER I DIVORCE YOU"
QUESTION: The Gemara teaches that any action which is within a person's ability to do ("b'Yado" -- "in his hands") is considered as though it has been done. The Gemara questions this principle from the words of Rebbi Oshiya, who rules that when a man gives a Perutah to his wife and says, "You are hereby Mekudeshes to me for after I divorce you," the Kidushin does not take effect after the divorce. According to the principle of "b'Yado," she should become Mekudeshes to him immediately after the divorce since it is within his ability now to divorce her and remarry her. The Gemara answers that although it is within his ability to divorce her, it is not within his ability to remarry her (since she must consent to it).
The Gemara's answer is difficult to understand. Although it is true that the man cannot force the woman to become Mekudeshes to him, in this case the woman has already given her explicit consent. When she accepts the money of Kidushin which will take effect after the divorce, she thereby consents to the Kidushin. Since she has expressed her explicit consent, and since the divorce itself is within the man's ability to perform, why is she not Mekudeshes to him immediately after the divorce? (See AVNEI MILU'IM 43:1.)
ANSWER: The TOSFOS RI HA'ZAKEN explains that the woman's consent today does not prove that she will consent to the Kidushin after the divorce takes effect. Today she is still bound to her husband and therefore she consents to the marriage. After the divorce she will be independent and might have a completely different attitude about being married. Therefore, there is no consent on the woman's part to the Kidushin which the man wants after the divorce.
This answer needs clarification. If the divorce is not considered "Mechusar Ma'aseh" (lacking an action) because it is within the husband's ability to divorce her now, and thus she is considered already divorced due to the principle of "b'Yado," the act of Kidushin also occurs at this moment! Why, then, must the woman consent to the marriage later if now she consents? Why is this case different from any other case of Kidushin in which the consent of the woman at the time of the Kidushin is all that is necessary for the Kidushin to take effect, regardless of whether or not she changes her mind afterwards?
Although the logic of "b'Yado" serves to remove the problem of "Mechusar Ma'aseh," in practice the act has not yet been done and "b'Yado" does not give the act the status of actually having been done in reality (see previous Insight). "B'Yado" suffices only to consider an act as a "Davar she'Ba l'Olam," but nothing can take effect until the act has actually been performed. Since, for all practical matters, the Kidushin takes place only after the divorce, the consent necessary for the Kidushin to take effect must occur at that time. (A. Kronengold)