Another case of muktze that is discussed by Beit Shammai and Beit Hillel is the case of an eli – a board of sorts that was ordinarily used to grind or crush things that cannot be done on Yom Tov. Can such a pestle be used for permitted food preparation – e.g. cutting meat – on Yom Tov, or is it considered muktze and cannot be moved?
In the Mishna, Beit Shammai forbids the use of an eli, while Beit Hillel permits its use.
Tosafot ask why the eli cannot be used according to Beit Shammai. Although the ordinary use of the eli is for acts that are forbidden on Yom Tov, this appears to be a case of a keli she-melakhto le-issur, le-tzorekh gufo – it is an implement which is ordinarily used for a forbidden purpose (which would make it muktze) for its own self – i.e. for another, permitted, purpose. Ordinarily such use – like cracking nuts with a hammer – is not considered muktze and would be permitted on Yom Tov. This question also appears in the Talmud Yerushalmi, which offers an answer similar to Tosafot, that this eli is muktze for other reasons beyond its being a utensil used for activities forbidden on Yom Tov. The additional source of muktze might be that it is a valuable implement which is muktze mahamat hisaron kis – because of its value – and cannot be used for another purpose (Tosafot) or it is a large utensil that has a specific place set aside and is not really used for purposes other than its central function (Tosafot R”id). According to this answer, Beit Hillel, who permits its use, does so only because they are lenient in order to encourage simhat Yom Tov – to enhance the joyousness of the holiday.
The Me’iri gives a different explanation to the Mishna. According to him, Beit Shammai forbids use of the eli because is appears to be a ma’aseh hol – a weekday activity – something that is not accepted by Beit Hillel.