Shehechiyanu: When D'Orysa Does Not Mean D'Orysa — Eruvin 40b
תלמוד בבלי מסכת עירובין דף מ/ב
והלכתא אומר זמן בראש השנה וביום הכפורים
Teshuvos Ri MiGash (§203) writes that the recitation of the berachah of Shehechiyanu on Rosh HaShanah and Yom Kippur is only D'Rabbanan — but that on Sukkos it is D'orysa!
R' Yosef Engel (Gilyonei HaShas here) notes that this clearly cannot be taken literally. The only berachah which may be D'Orysa is Birchas HaTorah. Rather, states R' Yosef Engel, Ri MiGash must mean that the Shehechiyanu of Rosh HaShanah and Yom Kippur is optional; while the Shehechiyanu of Sukkos is obligatory — but, ultimately, both are D'Rabbanan. Other instances of such usage, cited by Gilyonei HaShas, are in Teshuvos Ri MiGash §89; Teshuvos Tashbetz 2:182.
Nevertheless, writes R' Yosef Engel, even taken non-literally, Ri MiGash's ruling seems at odds with our sugya, which seems to conclude that the Shehechiyanu of Rosh HaShanah and Yom Kippur is obligatory. In resolution of this contradiction, he cites Tanya Rabasi, Hil. Rosh HaShanah §73 (in the name of Yerushalmi) that the Shehechiyanu of Kiddush is D'Rabbanan while the Shehechiyanu of Shofar is D'Orysa. Similarly, Maharil, Hil. Rosh HaShanah, writes that the Shehechiyanu of Kiddush does not cover the Shehechiyanu of Shofar because Kiddush is D'Rabbanan while Shofar is D'Orysa.
But, asks R' Yosef Engel, why do we not recite Shehechiyanu on Rosh Chodesh? Perhaps, he suggests, Kiddush Levanah is in lieu of Shehechiyanu.