The Shabat prohibition of Borer forbids separating items that are mixed together. Therefore, if food is mixed together with an inedible substance, one may separate them only if he removes the food (“Ochel”) from the inedible substance (“Pesolet”), and not the other way around. And even separating in this fashion is forbidden if the separation does not serve an immediate purpose.
Meaning, that one may separate the “Ochel” from the “Pesolet” in preparation for a meal that is about to be served, but not for a meal that will be served later in the day.
There is a debate among the halachic authorities as to whether these restrictions apply to separating kelim (utensils), as well. For example, if on Shabat a person’s cutlery is all mixed together, may he separate the utensils into different piles of forks and knives?
Clearly, it would be permissible to remove the utensil that one needs for immediate use from a pile of cutlery. The restrictions on separating cutlery will certainly be no stricter than those that apply to separating food and therefore just as one may separate “Ochel” from “Pesolet” for an immediate purpose, similarly, one may separate a utensil needed for immediate use.
However, the question is: can one separate cutlery for a purpose that is not immediate?
For example, if someone is setting the table on Friday night in preparation for Shabat lunch, may he separate the utensils to place the forks and knives in their appropriate places on the table?
This issue is subject to debate among the halachic authorities. The Taz (a”h) ruled that the restrictions of Borer apply to utensils and it would then be forbidden to separate them for a purpose other than immediate use. This is the ruling of the Mishna Berura, the Kaf Ha’Chaim (a”h) and the Ben Ish Chai (a”h).
Others, however, including the Mateh Yehuda (a”h) and the Ohr Sameach (a”h), maintained that the law of Borer applies only to items that can be actually mixed together. Utensils cannot be mixed the way foods can, as each utensil remains easily identifiable even if it is together in a pile with other utensils.
Therefore, according to these Rabanim, the restrictions of Borer cannot apply to utensils. This is the psak halachah accepted by Ha’Rav Ovadiyah Yosef (Shlit”a), in his sefer Yabia Omer. Thus, those who wish to act leniently in this regard may do so. Certainly when dealing with large utensils, such as platters, which cannot really be mixed together in a “mixture,” one may be lenient, as no “separating” is entailed at all.
This halachah applies to books as well. For example, if the books in the shul library are mixed together, the Shamash may separate them into different piles or arrange them in their proper places on the shelves. Like utensils, books cannot be said to become mixed together into a mixture and therefore the prohibition of Borer does not apply.