(R. Yochanan): This is the opinion of R. Elazar ben Azaryah, R. Yishmael and R. Akiva. However, Chachamim say that the Se'ir ha'Mishtale'ach atones.

Question: How does [Yom Kipur] atone?

Answer (R. Zeirah): Every tiny amount [of the day] atones a tiny amount.

Support (R. Chaninah - Beraisa): There is a stringency of the Se'ir [ha'Mishtale'ach] not found in Yom Kipur, and a stringency of Yom Kipur not found in the Se'ir. Yom Kipur [has a stringency - it] atones without the Se'ir, but the Se'ir does not atone without Yom Kipur;

There is a stringency of the Se'ir - it atones immediately, and Yom Kipur from when it gets dark [at the end of the day].

Rav Huna: I asked R. Yirmeyah [why Yom Kipur atones only from when it gets dark. When there is no Se'ir, it atones in place of the Se'ir!] He answered that we discuss when [the Mikdash stands and the Se'ir became Pasul, and] they intended to bring another Se'ir. (At a time of Churban, Yom Kipur atones when the Se'ir would be brought.)

Objection (R. Yosah ben Yosah): Does Hash-m not see the future [that they will not bring another?! The day] should atone immediately!