1) "YADAYIM SHE'EINAM MOCHICHOS"
QUESTION: Shmuel teaches that when a person attempts to make a Neder by declaring merely the words, "Mudrani Mimcha," his declaration is considered "Yadayim she'Einam Mochichos" and he is not prohibited from benefiting from his friend. The Neder does not take effect because Shmuel rules that "Yadayim she'Einam Mochichos" are not considered Yadayim. The RAN explains that according to Shmuel, no Neder takes effect whatsoever when a person declares the words "Mudrani Mimcha" alone.
However, the Ran cites another opinion that rules that even according to Shmuel, a person who says "Mudrani Mimcha" does become prohibited from speaking with the other person, but he is not prohibited from receiving benefit from him. This seems to be the opinion of the RAMBAM (Hilchos Nedarim 1:23).
According to this opinion, why does the statement of "Mudrani Mimcha" prohibit the person from speaking with his friend if it is "Yadayim she'Einam Mochichos"? Since the intention of his words is unclear, he should not be prohibited at all (according to Shmuel).
(a) The RAMBAM apparently maintains that "Mudrani Mimcha" is a Yad Mochi'ach for a prohibition of Dibur (speaking with the other person). When a person wants to prohibit himself from speaking to someone else he uses the phrase, "Mudrani Mimcha." The Gemara calls it a "Yad she'Eino Mochi'ach" only with regard to the prohibition of Hana'ah, benefiting from the other person. (When one says "Mudrani Mimcha she'Ani Ochel Lecha" -- "Mudrani Mimcha that I will eat from you," it is clear that he is prohibiting himself only from eating the food of the other person and not from speaking with him.)
How, though, does the Rambam understand the opinion that maintains that "Yadayim she'Einam Mochichos" are considered Yadayim? In the case of "Mudrani Mimcha," that opinion must agree that he is forbidden from speaking with the other person since it is a Yad Mochi'ach for the prohibition of Dibur, but that opinion must also rule that a prohibition of Hana'ah takes effect as well since it is a Yad Mochi'ach! How can one phrase imply two completely different concepts, a prohibition of Dibur and a prohibition of Hana'ah? Moreover, the phrase "Mudrani Mimcha" certainly implies a prohibition of Dibur more than a prohibition of Hana'ah. Why, then, is there a prohibition of Hana'ah altogether? (ROSH)
Perhaps the Rambam understands that according to the opinion that "Yadayim she'Einam Mochichos" are Yadayim, the person who made the Neder has the ability to clarify afterwards what he meant, and the Neder takes effect according to his clarification.