How could 2 days of Yom Tov be considered 1 kedushah b'zman hazeh, if the first is actually Yom Tov d'oraisa, and the 2nd only d'rabanan?
The gemara seems to indicate that when there was a doubt if the witnesses for the new moon did not arrive, then all the relevant cities were forced to keep 2 days and those 2 days were considered kedusha achas.
Today there is no doubt, yet we do not make havdalah between the first and second days of Yom Tov.
Both days of Rosh Hashana are d'oraisa.
Mendel, Lakewood NJ USA
Shalom R' Mendel,
It's great to hear from you!
1) As you correctly stated, in Chutz la'Aretz only the first day of Yom Tov is d'Oraisa whereas the second day is d'Rabanan. But that doesn't contradict the concept of "Kedushah Achas," because of the nature of the rabbinic enactment itself.
As the Gemara and Rashi in Beitzah 4b explain, according to the premise of Kedushah Achas, even after the calendar became fixed and there was no longer a real Safek, the egg laid on day one would remain Asur on day two, because the Chachamim intentionally maintained that the two-day observance for Chutz la'Aretz should be kept as an official Takanah.
Meaning, this was not just a Minhag that people adopted by themselves because of doubt -- that would be Shtei Kedushos. If that were the case, then theoretically once we would know the true calendar date, we would not have to keep the second day anymore. Rather, the Kedushah Achas view maintains that keeping two days as one long Yom Tov was established with the full force of Halachah.
See Rashi, especially DH Leima Kasavar Rav Asi, DH Sapukei Mesafka Lei, and DH v'Avdinan Trei Yomei.
2) When there was a doubt about whether the witnesses for the new moon arrived, the relevant cities would indeed observe two days. But the part of the very issue in question is: what was the nature of that observance -- Kedushah Achas or Shtei Kedushos (as we discussed above)?
3) As you correctly stated, today there is no doubt, yet we do not make Havdalah between the first and second days of Yom Tov. I think we can understand -- based on the same Gemara (Beitzah 4b, "v'Hashta d'Yadinan...") -- that the reason for this is because even if you hold Shtei Kedushos, nevertheless the warning to keep Minhag Avoseinu obliges us to treat the second day as Kodesh and not make Havdalah.
4) I am not sure in what circumstances you meant that the second day of Rosh Hashanah is mid'Oraisa. Nowadays, only the first day of Rosh Hashanah is mid'Oraisa.
May you continue to attain greatness in Torah and Yir'as Shamayim!
Warmly,
Yishai Rasowsky