Reuven vowed against 'benefit leading to food' from Shimon. May Shimon lend Reuven a hand mill?
A hand mill is explicitly listed among utensils used to prepare food (נָפָה, כְּבָרָה, רֵחַיִם, תַּנּוּר). Borrowing it is forbidden because it leads to food production — the very category prohibited by the vow.
Question 2
Shimon wants to pay a debt that Reuven owes to a third party. Is this permitted when Reuven is forbidden from Shimon's benefit?
The Rambam rules that Reuven receives nothing tangible — Shimon merely removes a claim against him. 'Preventing a claim' (מְנִיעַת הַתְּבִיעָה) is not in the category of forbidden benefit, whether the debt is the Temple half-shekel or a personal loan.
Question 3
May Shimon teach Reuven the Oral Torah when Reuven is forbidden from Shimon's benefit?
Since no wage may be charged for teaching Oral Torah, Shimon gives nothing of monetary value. The Written Torah, however, may carry a customary fee, making it forbidden unless local practice charges nothing.
Question 4
Reuven vowed not to benefit from Shimon's property before the Sabbatical year began. During the Sabbatical year, may Reuven eat produce from Shimon's field?
Once a prohibition takes effect via a vow, it persists. The Sabbatical year makes produce ownerless going forward, but cannot retroactively undo a vow that attached to the produce before Shemittah. Had the vow said 'my property' rather than 'this property,' or been taken during Shemittah, the result would differ.
Question 5
Why does the Rambam forbid Reuven from lending items to Shimon, even though it is Reuven who is forbidden from receiving Shimon's benefit?
The Rambam explicitly gives the reason: גְּזֵרָה שֶׁמָּא יִשְׁאַל מִמֶּנּוּ — 'a decree lest he borrow from him.' Lending invites reciprocal lending; selling invites reciprocal buying. The Sages erected these fences to protect Reuven from inadvertently receiving Shimon's forbidden benefit.