Hello Rabbi Haber,I hope you are doing well. I understand what you explained regarding Rabbi Eliezer being more motivated to derive Mashiv Haruach U'Morid Hageshem from Lulav if Nisuch Hamayim isn;t on the first day because if it indeed was on the first day, then he would derive it from Nisuch Hamayim because it's more directly related to water( as supposed to Lulav which is indirectly related). What I don't understand is why Rabbi Eliezer wants the hazkara to be mentioned on day one specifically! I understand on Amud aleph Tosafot said that Rabbi Eliezer holds one must לרצות לפני שאלה and he is not Makpid on Siman Klala like Rabbi Yehoshua but why day 1? why not day 2? why is he so determined to find a source to derive that Mashiv Haruch U'Morid Hageshem is to be said on the first day? Doesn't it usually work that something motivates you to want it to be a certain way? Thank you Rabbi for your time!

1. Title: Proposed Answer from Rabbi Haber
   AnonymousJoseph Basal, 

   Date: Jun 30, 2022

   Yasher koach for taking the time out to listen to my presentation of this Tosfos.  ברוך ד' שכוונתי to your  insightful question which I spent some time contemplating בשעתו and searching for answers in the מפרשים.  Since, unfortunately, we do not have תוספות הרא"ש or other parallel תוספות on תענית, it’s harder to research questions on Tosfos in Ta’anis.

   A proposed answer to your question: In general, any time a Tanna or Amora presents a halacha and then brings a proof from a passuk/Torah concept one can analyze what came first – the סברא or the דרשה?  In other words, did he – based on other aspects of Torah – theorize a certain halacha and then sought to verify it or find a support via דרשות OR did he enter the topic without any preconceived סברות, allowing the דרשות to generate the halacha?  This is debated between חכמי ישראל – see for example “The Dynamics of Dispute” by Rabbi Zvi Lampel )p. 22 ff. and the endnotes to Chapter 1).  I humbly suggest that both models could be true applying each one to different statements.  Certainly regarding דינים דרבנן such as the starting day of הזכרת גבורות גשמים, the passuk support is just an אסמכתא or parallel Torah concept and does not generate the halacha.  There, the view of סברא generating the halacha and then looking for Torah parallels is even more compelling since it is not the דרשה which generates the  דין דרבנן – otherwise it would be מן התורה!

   In light of all of the above, we can suggest that R. Eliezer views הזכרת גבורות גשמים on the first day of Sukkos as logically compelling.  It is logical to do the ריצוי during the entire Yom Tov, starting from the first day, before asking for rain after the Yom Tov.  But then R. Eliezer seeks a Torah parallel.  Once found, since כל דתקון רבנן כעין דאורייתא תיקון – all Rabbinic laws follow Torah precedents, we would follow the details of that Torah law applying them to the דין דרבנן which was initially ordained independently.  In this particular case, this would mean starting הזכרת גשמים at night if following the ניסוך המים model and during the day if following the לולב model.  Tosfos seem to maintain that if both models are available because ניסוך המים also starts on day one, then that model is preferable, as pointed out by מאירי and חזון איש, since it is more directly related to water.   But if ניסוך המים is on day 2, the סברא of starting on day 1 will “win out,” and we will use the less ideal parallel of לולב following its day precedent.

   R. Yehuda b. Beseira and R. Akiva, on the other hand, do not enter the discussion from a preconceived סברא of הזכרת גבורות גשמים starting on the first day of Yom Tov since regardless there will still be some ריצוי before the request for rain.  Therefore, they allow the more intuitive parallel of ניסוך המים – being more directly connected to water – to inform their start date for הזכרת גבורות גשמים, whether day 2 or day 6.