CONTINUING TO EAT WHEN SHABBOS COMES OR ENDS
Rav Hamnuna the elder was serving Rav Chananya bar Shalmiya and Talmidim of Rav; they told him 'see if [it is dark, and] Shabbos has arrived - if so, we will interrupt (remove the table) and Kove'a (establish) the meal for the sake of Shabbos.'
Rav Hamnuna: There is no need to do so - Shabbos itself is Kove'a!
(Rav): Just like Shabbos is Kove'a regarding Ma'aser (sometimes one may eat haphazardly without tithing - however, eating on Shabbos is never considered haphazard), it is Kove'a regarding Kidush (one must make Kidush before eating - automatically, the meal is l'Shem Shabbos)!
Assumption: Similarly, Shabbos is Kove'a regarding Havdalah (after Shabbos, one may not eat without saying Havdalah).
Rejection (Rav Amram): No - Rav said that Shabbos is Kove'a regarding Kidush, but not regarding Havdalah [it honors Shabbos to continue a Shabbos meal after dark];
This only permits continuing to eat [without saying Havdalah] - it does not permit starting a meal [after Shabbos before Havdalah].
The Heter to continue to eat applies only to [one who was] eating (he may also drink with the continuation of his meal), but not to [one who was only] drinking.
The Isur to continue drinking applies only to wine and beer, but not to water (one may even begin to drink after Shabbos before Havdalah).
He argues with Rav Huna:
Rav Huna saw a man drinking water before Havdalah - he asked him, are you not afraid of croup?!
(Beraisa - R. Akiva): One who eats any amount before Havdalah will die through croup.
Rabanan of Rav Ashi's academy held that one need not refrain from drinking water before Havdalah.
CAN ONE SAY KIDUSH HA'YOM DURING THE DAY?
Question (Ravina): If someone did not say Kidush on Shabbos night, does he say Kidush during the day?
Answer (Rav Nachman bar Yitzchak): Benei R. Chiya taught that if one did not make Havdalah on Motza'ei Shabbos, he makes Havdalah [at his first opportunity,] any time during the week - similarly, if one did not say Kidush on Shabbos night, he says Kidush during the day.
Question (Ravina - Beraisa): On Shabbos night and Yom Tov night there is Kidush over a cup [of wine] and mention [of the day] in Birkas ha'Mazon (Retzei or Ya'aleh v'Yavo); on Shabbos and Yom Tov [day] there is not Kidush on a cup, but there is mention in Birkas ha'Mazon.
If one who did not say Kidush on Shabbos night says it during the day, sometimes there is Kidush on Shabbos day!
Answer (Rav Nachman bar Yitzchak): The Beraisa discusses what is done l'Chatchilah.
Question (Beraisa): Honor of [the meal of] Shabbos day takes precedence over honor of Shabbos night - if one has only one cup of wine, he says Kidush ha'Yom over it, for it has precedence over honor of the day. (Kidush ha'Yom is the night Kidush, which contains the blessing 'Mekadesh ha'Shabbos'.)
If one who did not say Kidush on Shabbos night says it during the day, we should fulfill both, i.e. leave the wine for the day [to show greater honor to the day] and make Kidush ha'Yom then!
Answer: It is precious to do a Mitzvah in its [proper] time [even if it could be done better later].
Question: This is not so [regarding Berachos]!
(Beraisa): On Motza'ei Shabbos one blesses on wine, light, and spices; then he says Havdalah on the wine;
If he has only one cup, he [waits until after he eats, and] says all of them after Birkas ha'Mazon.
We do not say that it is precious to do a Mitzvah in its time [and he should make Havdalah immediately, even though later he will not be able to say Birkas ha'Mazon over a cup]!
Answer (Rav Nachman bar Yitzchak): I am not a Chacham [who thought of this myself], nor a prophet, nor do I say it in the name of an individual - rather, I have a tradition, and organized my learning until I understood well, and recite it in front of my Rebbe'im [who did not dissent], and this is what people teach in the Beis Medrash - we distinguish between the entrance of a [Kodesh] day and its exit;
When a Kodesh day comes, it is better to start it promptly [by saying Kidush] to show its dearness; when it leaves, we delay [Havdalah], lest we make it appear that the day was a burden [which we are eager to cast off].
We learn eight things from this Beraisa:
One who says Havdalah in Shemoneh Esre (Atah Chonantanu) must say Havdalah over a cup (the Beraisa requires the latter even though most people Mavdil in Tefilah);
Birkas ha'Mazon must be said over a cup;
There is a minimal size for [how much wine must be in] the cup of Berachah (otherwise, one could use half for Havdalah and half for Birkas ha'Mazon);
One who blesses must taste the wine (otherwise, he could make Havdalah and save all the wine for Birkas ha'Mazon);
If one tasted from the wine, he was Pogem it (disqualified it from being used for Birkas ha'Mazon - otherwise, he could Mavdil and save some wine for Birkas ha'Mazon. Tosfos - we assume that the Beraisa applies even if he has almost twice the Shi'ur of a Revi'is);
Even if one already ate [before Havdalah], he makes Havdalah;
One may say two Kedushos over one cup [if he lacks wine for two cups];
The Beraisa is Beis Shamai, according to R. Yehudah [who says that we bless on light before spices].