Yoma 81 a, b

I'll try to summarize some of the major concepts covered in today's daf.

• On Yom Kippur, we meet the mitzvah of not eating and drinking when we afflict our souls.
• two items that are similar in ritual purity and in measure can be combined; food and drink can be combined in this context, too:  
• Combining food and drink does not settle the mind
• If we consume something like brine, dry ginger, pepper, etc. (not usually consumed), we are exempt
• If we consume food and drink together in one lapse, we bring only one sin-offering
• If we consume food and also work on Yom Kippur, we bring two sin-offerings
• Usually, a punishment is preceded by a warning; afflictions are not preceded by warnings
• A baraita teaches that labour performed on Yom Kippur is punishable by karet
• The same baraita discusses whether labour performed on the extension of Yom Kippur is punishable by karet, too
• The baraita asks whether we can assume a warning before affliction because warning - punishment - labour and  thus warning - punishment - affliction
• Affliction is also used in Deuteronomy 22:24 "... because he has afflicted his neighbour's wife."  A warning precedes punishment for a rape, thus a warning should precede punishment for the affliction of Yom Kippur, as well*
• Yom Kippur is called "Shabbat" (Leviticus 23:32)
• The rabbis debate as to whether we extend Shabbat because it is called for us to afflict our souls beginning in the evening, or whether we are meant to afflict our souls only on the 9th of Av

We end the daf with a story about Giddel Bar Menashe from Birei Dineresh who publicly taught a community that drinking vinegar was permitted on Yom Kippur.  Vinegar was not normally drunk, and thus was permitted.  He learned that the following year, many people mixed vinegar with water and drank on Yom Kippur!  He corrected their actions by reminding them that he had spoken about pure vinegar, drunk sparingly, and only done after the fact but not ab initio.

The rabbis are trying to define what it means, practically speaking, to afflict one's soul.  The are forming their ideas about affliction, punishment, intention, and community influence as they argue with each other.  Outside of the Talmud, I have never learned that eating or drinking is permitted on Yom Kippur for any reason.  Our Sages understand people's behaviour and they understand human nature.  They are creating these guidelines and laws so that they will actually be used.

*It is painful to read the rabbis' use of the warning and punishment for rape as a simple comparison.  Mind you, in this particular example, I'm sure that the rabbis would have used another disturbing example, like murder, with similar flippancy.