Yoma 81b: Inedible Foods on Yom Kippur and the Klal of Inui

The Gemara (גמרא) on Yoma 81a-b records that Rebbe ruled drinking vinegar on Yom Kippur is a capital offense. Rav Gidel bar Menashe lectured in Biri d'Narish that the halacha (הלכה) is not like Rebbe. The townspeople diluted vinegar and drank it. Rav Gidel was upset, clarifying he never permitted drinking vinegar—only stating that after the fact (b'dieved) there is no kares for small amounts of undiluted vinegar, and he never addressed diluted vinegar at all. Most Rishonim understand this to mean drinking large amounts of undiluted vinegar carries kares, and diluted vinegar certainly does. The Rambam (רמב"ם), however, rules in Hilchos Shegagos 2:6 that drinking diluted vinegar is kares, but in 2:5 that even large amounts of undiluted vinegar do not carry kares—an apparent contradiction. The resolution hinges on understanding the nature of inui (affliction) on Yom Kippur. The pasuk commands "lo se'una"—one must be in a state of deprivation. Rabbeinu Yerucham and the Sefer HaShlomah understand inui to mean that one's discomfort must continuously increase throughout the day. Any food or drink that prevents this escalation—even if unpleasant—violates the prohibition and incurs kares. Thus, drinking large amounts of undiluted vinegar stops the escalation of hunger and thirst, even though it provides no pleasure, and therefore incurs kares. The Vilna Gaon in Shulchan Aruch explains this as violating "you are no longer in inui."