Gemara

5b (Abaye): Ambiguous Yados are valid;

(Rava): They are invalid.

Suggestion: Abaye holds like Chachamim, and Rava holds like R. Yehudah:

(Mishnah): The essential part of a Get is 'You are permitted to every man';

R. Yehudah says, it is 'v'Dein (and this Get) will be for you, Minai (from me), a Sefer of cutting...'

Rejection: Even Chachamim could agree with Rava. Chachamim allow ambiguous Yados only for Get, for one cannot divorce another man's wife (so it is clear that he divorces her), but not in other cases.

Kidushin 5b (Shmuel): If a man gave a woman money or something worth money, and said 'behold, you are Mekudeshes', or ... she is Mekudeshes. If he said 'I am your husband'... she is not Mekudeshes;

Similarly regarding divorce, if one gave her a Get and said 'behold, you are sent'... she is divorced. If he said 'I am not your husband'... she is not even doubtfully divorced.

Question (Rav Papa): Here, Shmuel holds that a Yad (an abbreviated expression) that is not clear (how to complete it) is invalid (he did not specify that she is Mekudeshes to or divorced from him). Elsewhere, he taught differently!

(Mishnah): If one said 'I will be', this is acceptance of Nezirus.

Question: Why is this? Perhaps he meant 'I will (be in a) fast'!

Answer (Shmuel): The case is, a Nazir passed in front of him at the time.

Inference: If a Nazir was not around, it would not be acceptance of Nezirus!

Answer (Abaye): Shmuel discusses one who said '(you are Mekudeshes) Li (to me).'

His Chidush is that the latter expressions (of Kidushin and divorce) are invalid.

Gitin 85b - Question: What do R. Yehudah and Chachamim argue about?

Answer: Chachamim hold that an ambiguous Yad is valid. Even though he did not write 'v'Dein...', it is clear that he divorces her through the Get.

R. Yehudah holds that an ambiguous Yad is not a Yad. If he does not write 'v'Dein...', perhaps he divorces her verbally, and the Get is just for a proof.

Nazir 62a - Question: What do we learn from "Yafli", which is written regarding Nezirus?

Answer: It teaches (regarding Nezirus) about ambiguous Yados:

(Abaye): Ambiguous Yados are valid Yados.

(Rava): Ambiguous Yados are not valid Yados.

Question: This answer works for Abaye, but not for Rava!

Rishonim

Rif (Nedarim 1a): Shmuel holds like R. Yehudah, that ambiguous Yados are invalid.

Rosh (Nedarim 1:2): The Halachah follows Rava against Abaye, that ambiguous Yados are invalid.

Rif (Kidushin 2a and Rosh 1:2): Shmuel taught that if a man gave to a woman money and said 'behold, you are Mekudeshes Li', she is Mekudeshes. Similarly, if one gave a Get and said 'behold, you are sent', she is divorced.

Question (Rosh): This is only because he said 'you are Mekudeshes Li.' Without 'Li' she is not Mekudeshes, for ambiguous Yados are invalid. In Nazir, we conclude that ambiguous Yados are valid!

Answer (Rosh): Kidushin without 'Li' is not a Yad at all. People often make Sheluchim to be Mekadesh, so it is not clear at all to whom he is Mekadesh her. Even Abaye agrees. This is why he needed to establish Shmuel to discuss when he said 'Li'. He could not say 'yes, he holds like me that ambiguous Yados are valid', for no one says so in this case. In Nedarim we conclude that ambiguous Yados are invalid, like Rava. Therefore, if he did not say 'Li', we do not even require a Get. The text in Nazir 62a says that Rava says that ambiguous Yados are valid, and asks what Abaye learns from "Yafli". Surely the opinions of Abaye and Rava were reversed. If not, obviously, Abaye learns from "Yafli" that Yados Nezirus must be clear!

Teshuvas Rosh (35:5 b'Emtza, citing Rabbeinu Meir): In Nazir, Abaye and Rava argue about Yados Nezirus. Rava learned from "Ish Ki Yafli Neder b'Erkecha" that Nedarim require Hafla'ah (clarity), so ambiguous Yados are invalid. A Hekesh teaches similarly about Nezirus. It says "Yafli" also regarding Nezirus. This is a Mi'ut after a Mi'ut, which comes to include (ambiguous Yados are valid). We ask how Abaye expounds Yafli written regarding Nedarim. (He uses Yafli of Nezirus to disqualify ambiguous Yados Nezirus.)

Note: Our text in Nazir says that Abaye says that ambiguous Yados are valid, and asks what Rava learns from "Yafli". This remains difficult for the Rosh above! Based on Rabbeinu Meir, we can say that Abaye expounds Yafli written regarding Erchin and Nezirus to be a Mi'ut after a Mi'ut to include ambiguous Yados (they are always valid). We ask what Rava learns from the extra Yafli.

Ran (Kidushin 2a DH Omar): Some say that even though ambiguous Yados are invalid, we are stringent about Gitin and Kidushin, and she is Safek Mekudeshes. Even though a Get without v'Dein is unclear, it seems that if one wrote only 'you are permitted to every man' and the rest of a standard Get, she is disqualified from Kehunah, and Kidushin takes effect on her (mi'Safek), for the question was never settled. This is not a proof. We are unsure about Get, for perhaps it is clear that he divorces her with the Get, but regarding Kidushin, if he did not say 'Li' there is no concern, like Rava taught.

Rambam (Hilchos Ishus 3:1): To be Mekadesh ... he says 'you are Mekudeshes Li.'

Magid Mishneh: The Ramban, Rashba and many Meforshim say that if he did not say 'Li', she is not Mekudeshes, for ambiguous Yados are invalid.

Mordechai (Sof Gitin 470): The Halachah follows R. Yosi, who say that if a man was talking with a woman about Kidushin and gave the money silently, she is Mekudeshes. (Saying 'you are Mekudeshes', without Li, is talk about Kidushin!) Some say that we require that both of them were talking. I disagree. The Gemara asked 'in which case do we ask about the ambiguous expressions (Ezrasi...)?' It did not suggest that only he was talking about Kidushin! In practice, one must be stringent if he did not say 'Li.' Even though the Halachah follows Rava, we said that Rava could agree regarding divorce, for David cannot divorce Levi's wife. Likewise, he could agree about Kidushin, for one cannot Mekadesh a woman to another man. Some disagree (perhaps he is a Shali'ach), but they have no basis.

Poskim

Shulchan Aruch (EH 27:4): If a man (gave Kidushin and) said 'you are Mekudeshes', without saying 'Li', she is not Mekudeshes.

Chelkas Mechokek (11): This is even if both of them understood that he is Mekadesh her to him. It does not depend on intent. The words must indicate this. All the more so, if he gave her in silence she is not Mekudeshes.

Rema: This is primary. Some are stringent to say that it is Kidushin.

Beis Yosef (DH uvi'Teshuvas and DH veha'Ran): The Ramban (130 - really, the Rashba) and Rashba (1:774) are in doubt if he did not say 'Li'. The Rivash (266) doubts the authenticity of these Teshuvos. The Rif and Rambam discuss only when he said 'Li'. This implies that without this, it is not Kidushin. A case arose, and the Rosh (Teshuvah 35:5) did not require a Get.

Gra (23): The Rivash did not totally reject the Teshuvos. Shmuel said 'and similarly regarding divorce...' regarding valid and invalid expressions, but not regarding Yados. Shmuel did not mention 'Li'.

Bach (EH 27 DH ul'Inyan): The Ramban and Rashba were lenient l'Halachah, but in practice (Teshuvah 130 and 774) they were stringent. Surely we must be stringent in a matter that depends on texts. The text in Nazir says that Rava holds that ambiguous Yados are valid.

Chelkas Mechokek (12): The Rema connotes that we are concerned for the stringent opinion in practice, but in Darchei Moshe he connotes that we are not.

Beis Shmuel (14): We may be lenient if there is another Safek, i.e. even had he said 'Li' there would be a Safek. The Ben Lev and Maharit argue about whether or not Shiduchin makes the Yados unambiguous.