The Gemora (Nedarim 55b-56b) discusses the status of two people who are partners in a courtyard. They both have use rights, but it may depend on bereirah to determine exactly when each one has ownership at a given time.
The Gemora (Beitza 37b-38a) discusses cases of partners who split their joined item, insofar as techumim ownership. Bereirah allows us to consider the ultimate allocation reflective of the original true ownership.
This case is discussed by Rabbi Yochanan in our Gemora, and appears in many other Gemoros.
This case is discussed by Rabbi Meir and Rabbi Yehudah in our Gemora, and appears in many other Gemoros.
Choosing a Techum
The Gemora (Eruvin 36b-38a) discusses various Eruvei Techumim, where the actual details of the Eruv are left for later clarification, using Bereirah. The Gemora includes a lengthy discussion of Rabbi Yehudah’s position on Bereirah, based on multiple conflicting sources.
Why does (or doesn’t) it work?
Tosfos (Eruvin 37b Ela) states that those who do not accept bereirah feel that later designation is meaningless, and therefore the action is not effective at all. In our case, this means that the separation that will happen after Shabbos is meaningless, and therefore, the declaration at the onset of Shabbos has no wine to take effect on, and it not effective at all. Rashi (Chulin 14b osrin), on the other hand, states that those who do not accept bereirah simply hold that the later designation cannot resolve the initial unclarity. In the case of the wine, when the person declares that he is taking the tithes from wine that will be designated later, the tithes now exist in the wine, but the person cannot designate them later. Therefore, this wine has indeterminate tithes, and none of it can be used.
See Shaarei Yosher (3:22 v’af shera’isi) for a more detailed discussion of how bereirah does work, and what are its limitations. See Shiurei R. Dovid Lifshitz (Hulin, #29) for a further discussion of this dispute.
How much is unclear?
The Ran in Nedarim (55b v’ika) suggests that the case of partners’ use in a courtyard can be considered full ownership, even according to those who generally do not accept bereirah, since the bulk of the "split" is already done, with only the exact time that it will be used left for later clarification.
Will it definitely be clarified?
Tosfos (Gittin 25b Rabbi Yehudah) states that some cases of bereirah are less acceptable, since there may never be any clarification. For example, as opposed to our case of the wine - where some wine will be taken, but it’s not known which - a case of one who consecrates the coin that he will take from his pocket, is a case where it’s possible that no coin will be chosen at all.
The Gemora in Gittin (25a-b) raises the possibility that bereirah may be more acceptable in the case where the area left for later clarification depends on another party. If bereirah is unacceptable because the party doing the action must decide before acting, then if the only clarification is external, the active party has done his part, and left the rest up to something else. Examples of this are:
1. A person who betroths a woman, but stipulates that it will only take effect if the woman’s father agrees.
2. A person who gives his wife a Get, which should be effective one moment before he dies. This is making it dependent on outside party, i.e., Hashem.
There are cases where the Torah states an explicit detail, which overrides the general rules of bereirah.
The Torah explicitly states that a Get must be written "la" - for her (the wife), and from this the Gemora learns (Gittin 2b) that a Get must be written "lishma" - explicitly for the wife’s sake. From this verse, Tosfos (24b l’aizo) suggests that even those who accept bereirah may invalidate a Get which was written for the sake of "the wife that I choose"
The Gemora on our daf mentions the case of brothers who split their father’s estate as a case of bereirah. Tosfos (Gittin 48a Ee) suggests that, even without bereirah, inheriting brothers could be not subject to return on the Yovel year, due to the inherent nature of inheritance and Yovel.
Torah vs. Rabbinic
The Ri in Tosfos (Nedarim 56b) rules that we accept bereirah in all areas of halachah. The Rambam (Eruvin 8:7, Trumos 1:21, Yom Tov 5:20) rules that in Rabbinic areas of halachah, we accept bereirah, while in areas of Torah halachah, we do not accept bereirah.