Early Havdalah

This post is based on a shiur by Rabbi Yosef Elefant. 

The Gemorah Berachot (27b) says a person is allowed to say havdalah even when it is still light outside and it is still Shabbos.  If that's the case, why would we not say havdalah early, on Shabbos itself, when tisha b'av is Sunday? 

In order to address this question we first need to understand the din itself.  Why is one allowed to say havdalah early?  Tosfos on the page writes that this din of saying havdalah is true only in a pressing situation where one must leave immediately after Shabbos to do a mitzvah but otherwise one may not say havdalah early.  However, the Rambam does not mention this caveat.  What is this machlokes about? 

Before the Gemorah says one can do havdalah while it is still Shabbos it says one can say kiddush when it is still daylight on Friday.  Tosfos in Pesachim (99b) and the Rosh Arvei Pesachim siman 2 explain the reason one can recite kiddush while it is still day is because of the principle of tosefes Shabbos, that one can extend Shabbos into Friday.  That works to explain why you can do kiddush early but that does not help us for havdalah; why you can do havdalah early?

The Rambam in the Laws of Shabbos (29:11) says יֵשׁ לוֹ לְאָדָם לְקַדֵּשׁ עַל הַכּוֹס עֶרֶב שַׁבָּת מִבְּעוֹד יוֹם אַף עַל פִּי שֶׁלֹּא נִכְנְסָה הַשַּׁבָּת. וְכֵן מַבְדִּיל עַל הַכּוֹס מִבְּעוֹד יוֹם אַף עַל פִּי שֶׁעֲדַיִן הִיא שַׁבָּת. שֶׁמִּצְוַת זְכִירָה לְאָמְרָהּ בֵּין בִּשְׁעַת כְּנִיסָתוֹ וִיצִיאָתוֹ בֵּין קֹדֶם לְשָׁעָה זוֹ כִּמְעַט:  The Rambam holds the reason one can say havdalah and kiddush while still day is because of the same reason, the mitzvah is to talk about Shabbos around the time of Shabbos, not on the day itself but as one is ushering in or exiting Shabbos.  The Rambam holds that the mitzvah of kiddush and havdalah are the same mitzvah; both are declarations of the kedusha of Shabbos.  Havdalah is not an expression of chol, it is an expression of Shabbos and hence may be declared even as it is still Shabbos. 

The Tur (556) brings the Behag says one should not recite havdalah early on Shabbos before tisha b'av because if one does so it would be prohibite for them to continue drinking.  Why would the person be prohibited from drinking just because he recited havdalah?  We see the Behag holds that by saying havdalah while it is still shabbos one is already bringing in the chol and although the issur melacha is still in place, there is a semi-status of chol already pronounced.  The Behag is the opposite of the Rambam.  He holds that havdalah is an expression of leaving Shabbos and therefore when one does havdalah early it is because one is to an extent leaving the kedusha of Shabbos behind.

The Tur (293) brings from the Ritz Gayos that now that the custom is to follow the opinion of the Rabannan to daven maariv after dark, not like Rebbe Yehuda that says one can do it from plag mincha one should not say kiddush or havdalah early.  What does a machlokes about davening times have to do with whether one can say kiddush or havdalah when it is still day?  The Gra in Maaseh Rav (117) says one must daven maariv before saying kiddush (not like the Magen Avraham 271:5.)  In that light we can understand that if you can't daven yet, you can't say kiddush yet.  But why must one daven maariv in order to say kiddush?  It must be that davining maariv is what already makes it called the night time.  If one davened maariv they have declared it to be night and the dinim of the night can already extend into the previous day but without maariv it is still Friday and one can't make kiddush or it is still Shabbos and one can't make havdalah.  The davining is what gives at least a partial status of night.  This is similar to the Behag that one can make the status of the night extend into the previous day but he holds that can only happen through tefillah.  

Getting back to Tosfos and how he will learn havdalah.  It must be Tosfos learnt along the lines of the Ritz Gayos or the Behag but he holds it only suffices for havdalah to be able to have an early removal of the kedusha of Shabbos but to fulfill kiddush one needs bonafide kedushas Shabbos it would not suffice to have a quasi status of the night extended with a kiddush or tefillah and therefore needs to evoke the principal of tosefs Shabbos.  Because Tosfos holds that one is declaring it to be chol early by saying havdalah when it is still Shabbos he only allows it in a pressing situation.  The Rambam that holds it does not make it chol, on the contrary, havdalah is a way of affirming the holiness of Shabbos, has no problem with doing havdalah on Shabbos.  However, we are left with the question according to the Rambam dwhy should one not say havdalah on Shabbos when tisha b'av is sunday?