Rif Pesachim 21b {Pesachim 104a continues; 105a; 107a}

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21b
{Pesachim 104a continues}
Yom Kippur and Motzaei Yom Tov going into Chol HaMoed, and from Motzaei Shabbat going into Yom Tov, but not from Motzaei Yom Tov going into Shabbat.

We learn in the slaughtering of Chullin, at the end of the first perek {26a}: Yom Tov which fell out in the middle of the week, he says "who divides between holy and profane, and between light and darkness, and between the seventh day to the six days of work." What is the reason? He is listing an arrangement of divisions.

They learnt {in a brayta}: The nights of Shabbat and the nights of Yom Tov have sanctification on them over a cup and they have in them mention in the birkat haMazon.

{Pesachim 105a}
Rav Chanina bar Shelemia and the students of Rav were sitting at a meal, and Rav Hamnuna the elder attended over them. They said to him: go see if the day has broke {nagah yoma = it has become night} in which case we will break and establish the Shabbat.
He said to them: You do not need to establish her, for she establishes herself.
For so said Rav: Just as Shabbat establishes for maaser, so does it establish for kiddush.

To explain: Anything which he eats during the week on a temporary basis and he did not already take out from it maaser, it is forbidden to eat from it on Shabbat unless he took off maaser. What is the reason? Since it is written {in Yeshaya 58:13}

יג אִם-תָּשִׁיב מִשַּׁבָּת רַגְלֶךָ, עֲשׂוֹת חֲפָצֶךָ בְּיוֹם קָדְשִׁי; וְקָרָאתָ לַשַּׁבָּת עֹנֶג, לִקְדוֹשׁ יְהוָה מְכֻבָּד, וְכִבַּדְתּוֹ מֵעֲשׂוֹת דְּרָכֶיךָ, מִמְּצוֹא חֶפְצְךָ וְדַבֵּר דָּבָר.

13 If thou turn away thy foot because of the sabbath, from pursuing thy business on My holy day; and call the sabbath a delight, and the holy of the LORD honourable; and shalt honour it, not doing thy wonted ways, nor pursuing thy business, nor speaking thereof;

and he needs to make the Shabbat a delight with food and drink, all fruits go out from the status of temporary and on Shabbat become like those which are designated to eat from them on Shabbat in a permanent status. And (thus) if he took maaser off them while it was yet day he may eat from them on Shabbat, and if he did not take maaser off them while it was yet day, it is forbidden to take off maaser once it became dark. And even if it a doubt whether it is dark {=Shabbat} or whether it is not dark, we do not take maaser off of the certain {ly tevel food}, and from that time, Shabbat established them for maaser and it is forbidden to eat from them on that Shabbat for they have been established for Shabbat.

And so too, when it is {a time of} doubt whether it is dark and a doubt whether it is not dark, the Shabbat establishes itself for sanctification {=kiddush} and we do not need to investigate if it is dark or not for it has established itself -- once it is doubt whether dark and doubt whether it is not dark, you should spread a cloth, make kiddush, and return to your meal.

They thought from this that just as it established for kiddush and they need to interrupt the meal to make kiddush, so does it establish for havdala and they need to interrupt the meal for havdala.
Rav Amram said to them: So said Rav: For havdala it does not establish.

And the point of practical distinction is in terms of interrupting -- that he does not interrupt his meal, but to begin his meal, he should not begin. And in terms of interrupting, they only said this regarding eating, but drinking, he interrupts. And drinking, too, they only said regarding wine and beer, but water, we have no concern with it. For the Sages in the academy of Rav Ashi were not insistent regarding water. And so is the halacha.

Ravina inquired of Rav Nachman bar Yitzchak: one who did not make kiddush on erev Shabbat, may he make kiddush the entire day?
{Pesachim 107a}
And the conclusion: Rava said: The halacha is that he who has tasted {food} may make kiddush; and he who has tasted may make havdala; and one who did not make kiddush on erev Shabbat may make kiddush throughout the entire day; and one who did not make havdala on Motzaei Shabbat may make havdala throughout the entire day, but not on the flame.

However, we deduce