1) KIDUSHIN WITH A RING
HALACHAH: The Mishnah teaches that a woman becomes betrothed (Mekudeshes) through Kesef or Shaveh Kesef. Accordingly, a man may give a coin to a woman for Kidushin. The REMA (EH 27:1) writes, however, that the present practice is not to give a coin for Kidushin, but to give a ring. What is the reason for this practice?
(a) The BEIS SHMUEL (EH 27:1, 31:5) cites the MORDECHAI who writes that one should not use a coin to be Mekadesh a woman. The Beis Shmuel explains that this was a rabbinic enactment.
The AVNEI MILU'IM points out that the HAGAHOS MORDECHAI (Kidushin #488), which is apparently the source for the Beis Shmuel's words, does not write that one should not use a coin. Rather, he questions why a coin may be used for Kidushin. The Gemara in Kidushin (8a) explains that if a woman thinks that the object which the man gives is of a certain value and the object is of a different value, the Kidushin does not take effect. The Gemara in Bava Metzia (45b) rules that a coin may not be used to make a Kinyan Chalifin because the value which a person ascribes to a coin is the stamp or form on the coin (since the coin is unusable without the stamp), but the stamp on the coin often changes (such as when a new king is appointed), and thus it may not be used for a Kinyan Chalifin. Accordingly, one also should not be permitted to use a coin for Kidushin, since the woman relies on the stamp, but the stamp will change.
Although the Hagahos Mordechai raises this question, he does not discourage the use of a coin for Kidushin.
The Avnei Milu'im answers the question of the Hagahos Mordechai based on the words of RASHI in Bava Metzia (45b, DH Matbe'a). Rashi writes that a coin without a stamp may not be used for Kinyan Chalifin because Chalifin must be performed with a complete object. A coin without a stamp is an incomplete object. According to Rashi, the Gemara in Bava Metzia does not mean that the reason why a coin may not be used for a Kinyan Chalifin is that its true value is not what people assume it to be. Rather, the Gemara means that even when it bears its stamp (and its value is what people assume it to be), it is considered incomplete since the stamp might change tomorrow. With regard to Kidushin, this concern poses no problem because even an incomplete object may be used for Kidushin as long as it is worth a Perutah. Since the coin with a stamp is worth what the woman thinks it is worth, the Kidushin takes effect.
(b) The SEFER HA'MIKNAH (Chidushim to EH 50:1) and the TZAFNAS PANE'ACH (Hilchos Ishus 3:1) point out that the custom to be Mekadesh a woman with a ring may have been adopted when it became the practice to perform the Nisu'in immediately after the Kidushin (instead of some months after the Kidushin). When the Nisu'in is performed, all of the wife's property becomes Nichsei Milug and the husband is entitled to its produce (Peros). If the husband would give the wife money and then perform Nisu'in immediately afterwards, the money would be worth much less to her since she would have rights only to the body (Guf) of the coin and not to the Peros (the spending value) of the coin. Such a situation would be akin to a case in which the man tricked the woman about the amount of money he intended to give for Kidushin, or to a case in which the man keeps some of the amount for himself. Therefore, the Chachamim instituted the custom that the man give a ring, an object which the woman wears. The Gemara in Kesuvos (54a) teaches that a married woman retains the rights to the use (Peros) of her clothing and personal objects. When she receives a ring, she receives the full value of the ring even when the Nisu'in is performed immediately afterward. (The Tzafnas Pane'ach cites the Yerushalmi in Nazir 5:2 which states that a woman's jewelry is considered her possession and not the possession of her husband.)
(c) The SEFER HA'CHINUCH (#552) writes that the source for the practice to give a ring for Kidushin is the consideration to provide the woman with something which will be in front of her always and remind her of her devotion to her husband (as the verse says, "Tie them on your fingers, inscribe them on the tablet of your heart" (Mishlei 7:3), a reference to the Mitzvos of the Torah).
(d) The REMA himself cites the TIKUNEI ZOHAR (beginning of Tikun 5, and Tikun 10, page 25b) as a source for the practice to give a ring for Kidushin.
A symbolic source for this practice may be the verse in Yirmeyahu (31:21) which states that at the time of the final redemption, "the woman will look around (Tesovev) for the man," in contrast to the ways of the world now when the man searches for a wife (as the Gemara says on 2b). Rashi and the Radak explain that the metaphor of the verse expresses the Jewish people's search for ways to return to Hash-m. The verse compares the final redemption to Kidushin, the coming together of Hash-m and His people. When a man and woman marry, he gives her a ring -- a circular ("Tesovev") ornament, an allusion to the Jewish people's longing for the "Kidushin" of the final redemption as described in the verse of "Tesovev Gaver."
2) THE DIFFERENT WAYS TO EFFECT KIDUSHIN
QUESTION: The Mishnah teaches that a woman becomes betrothed (Mekudeshes) through Kesef, Shtar, or Bi'ah.
RASHI explains how the act of Kidushin is performed in each of these cases. When a man is Mekadesh a woman with Kesef, he gives her money and says, "Harei At Mekudeshes Li."
When a man is Mekadesh a woman with a Shtar, he writes in the Shtar, "Harei At Mekudeshes Li," and gives the Shtar to her. (The source for these two forms of Kidushin is the Gemara later (5b and 9a) and the Tosefta 1:1.)
When a man is Mekadesh a woman with Bi'ah, the man lives with her and says, "Hiskadshi Li b'Vi'ah Zu."
There are several obvious differences between the way Rashi describes Kidushin performed with Bi'ah and the way he describes Kidushin performed with Kesef and Shtar:
1. When he describes what the husband says for Kidushei Bi'ah, Rashi writes "v'Amar" -- "and he said...." In contrast, when he describes what the husband says for Kidushei Kesef and Shtar, Rashi writes "v'Omer" -- "and he says." (In RASHI KESAV YAD and the RAN, the word "v'Omer" indeed appears with regard to Kidushei Bi'ah.)
2. Rashi writes that for Kidushei Bi'ah, the man must mention the words "b'Vi'ah Zu" -- "[You are hereby betrothed to me] with this act of Bi'ah." In contrast, for Kidushei Kesef and Shtar, the man does not need to mention the Kesef and Shtar with which he betroths her.
The RAMBAM (Hilchos Ishus 3:5) and the SHULCHAN ARUCH (EH 33) also include the words "b'Vi'ah Zu" in the man's declaration of intent for Kidushei Bi'ah but not in his declaration of intent for Kidushei Kesef and Shtar. (The ME'IRI writes that it is not necessary to say "b'Vi'ah Zu.")
3. Rashi writes that for Kidushei Kesef and Shtar the man states, "Harei At Mekudeshes Li," but for Kidushei Bi'ah he writes that the man states, "Hiskadshi Li."
What is the reason for these differences?
ANSWERS: The Acharonim explain that when a man performs Kidushei Bi'ah, he must specify his intent more clearly than when he performs other forms of Kidushin. They suggest several reasons for why this is necessary.
(a) The Gemara later (12b) teaches that the Amora'im prohibited one from betrothing a woman with Bi'ah because of the concern for promiscuity. Perhaps this is why Rashi writes "v'Amar" -- "he said" in the past tense, which implies that only b'Di'eved does the Kidushin take effect through Bi'ah, but l'Chatchilah a man should not betroth a woman through Bi'ah. (BIRUREI HA'SHITOS in the name of the OR CHADASH)
This reasoning also explains the other differences between Kidushei Bi'ah and Kidushei Kesef and Shtar. Since one is prohibited from betrothing a woman with Bi'ah, the woman will not suspect that he intends to betroth her with Bi'ah unless he states so explicitly. Without an explicit declaration of his intent, she will assume that the Bi'ah is merely an act of promiscuity. The man must say "Hiskadshi Li" (a request, and not a statement) because he needs her explicit consent to participate in an inappropriate form of Kidushin.
(b) The IMREI BINYAMIN cites the CHIDUSHEI HA'RIM who explains that the witnesses do not need to see the act of Bi'ah itself in order for Kidushei Bi'ah to take effect. It suffices if they see the Yichud and hear the husband say that he intends to betroth her with Bi'ah. Their witnessing of the Yichud is akin to the witnessing of the Bi'ah itself because of the principle of "Hen Hen Edei Yichud, Hen Hen Edei Bi'ah" (Gitin 81b; see ME'IRI who cites differing opinions with regard to whether this rule applies to Kidushin).
This approach explains all three differences. Since the man must state his intent to perform Kidushin in front of witnesses, and the Bi'ah is performed afterwards not in the presence of witnesses, Rashi writes "v'Amar" -- he already said "Hiskadshi Li" earlier, when he was in the presence of witnesses.
Since the man's declaration refers to his intent to perform Kidushin in the future (with Bi'ah, after the Yichud), he says "Hiskadshi" rather than "Harei At Mekudeshes."
Since the act of Kidushin is not performed at the moment of, or immediately after, his declaration of intent, the form of Kidushin which he intends to use is not clear; perhaps he thinks that Yichud alone effects a Kidushin. Therefore, he must say, "Hiskadshi Li b'Vi'ah Zu."
(c) Perhaps Rashi maintains that the man does not need to say "with this Kesef" ("b'Kesef Zeh") or "with this Shtar" ("b'Shtar Zeh") when he gives the Kesef or Shtar to the woman and afterwards (while she is holding the Kesef or Shtar) states that he betroths her. This is implicit in Rashi's words that "he gives her Kesef and he says to her 'Harei At Mekudeshes.'" Since she is holding the Kesef or Shtar at that moment, he does not have to specify the method he uses to make the Kidushin (because it is obvious). Similarly, he does not have to ask her whether she consents to the Kidushin; he may state simply, "You are Mekudeshes to me," and she shows her consent by not returning the Kesef or Shtar.
In contrast, when he intends to betroth her with Bi'ah and tells her at the time that he wants to betroth her, her silence does not show her consent. Perhaps "Yitzrah Albeshah" (Kesuvos 51b) -- she is silent because she is overcome by her Yetzer ha'Ra and not because she wants to marry him. Therefore, before he performs the act he must clearly explain that he wants to betroth her with the act so that her consent to the act will show that she also consents to the Kidushin. This explains why Rashi writes, "v'Amar Lah," he said to her in the past tense, before the act was done. This also explains why he must say "Hiskadshi Li" and request her to agree to Kidushei Bi'ah (since the act has not yet been performed). He must say "b'Vi'ah Zu" since the object or act which effects Kidushin is not yet present and it is not clear what he intends to use to effect the Kidushin.
Nowadays, it is customary to perform Kidushin with Kidushei Kesef and to state explicitly "b'Taba'as Zo" ("with this ring"). The source for this practice may be based on the above explanation. Since the common practice today is for the man to make the declaration of Kidushin before he gives the ring to the woman, the man must specify the object or act which he intends to use to effect the Kidushin so that it is clear to the woman that the Kesef (ring) is for the sake of Kidushin.

2b----------------------------------------2b

3) KIDUSHIN AGAINST THE WILL OF THE WOMAN
QUESTION: The Gemara asserts that had the Mishnah said "ha'Ish Koneh," one might have thought that a man may betroth a woman against her will. Therefore, the Mishnah states "ha'Ishah Niknis" to teach that a woman may be betrothed only with her consent.
What is the basis for the Gemara's suggestion that a man could betroth a woman against her will? It is obvious that a woman must consent to marriage.
ANSWER: The RASHBA explains that the Gemara in Bava Basra (47b) teaches that if a person agrees to sell his item under coercion, the sale is valid and binding. Since the seller receives something of value (money) in return for the item, it is assumed that his consent was genuine despite the fact that he was forced to consent to the transaction.
The Gemara there (48b) cites a dispute among Amora'im with regard to whether this principle applies to Kidushin as well. When a man coerces a woman to accept Kidushin from him, is the Kidushin valid? Mar bar Rav Ashi rules that the Kidushin is not valid. Since the man acted improperly, the Rabanan annulled ("Mafki'a") the Kidushin.
The Gemara here follows the view of Mar bar Rav Ashi. The Gemara explains that the Mishnah states "ha'Ishah Niknis" instead of "ha'Ish Koneh" in order to teach this Halachah -- if a woman consents to Kidushin under duress, the Kidushin is not valid.