Today's daf is sponsored by Tali Oberman in honor of her grandmother, Miriam Sklar, who has reached the incredible milestone of 90.
A braita has a more expanded version of the debate between Rabbi Yishmael and Rabbi Akiva about whether or not the oath of expression for which one is obligated to bring a sliding-scale offering includes oaths regarding events that already happened (about the past). Each uses a different exegetical principle in reaching his conclusion, based on the method adopted by their teachers, Rabbi Nechunia Ish haKane, klal and prat (Rabbi Yishmael), and Nachum Ish Gamzu, ribui and miyut (Rabbi Akiva).
An oath of expression is only brought if the person is shogeg, unwitting, when they forgot their oath, but not if they did it on purpose or if it was totally beyond their control. The Gemara brings an example of an oath that would be beyond one's control.
A braita extrapolates from the verse that an oath of expression is only brought by one who forgot the oath but not the object. Is it possible to find a case of remembering that oath, but forgetting the object?
Rava asks Rav Nachman what would be the case if one forgot both the oath and the object. This question is left unanswered as one can make an argument both to obligate and to exempt.
Rava asks Rav Nachman what would be a case of shogeg for an oath of expression about the past? Rav Nachman answers that one who remembers the oath, but does not know that one is obligated to bring a sacrifice. This seems initially to match only Munbaz's approach in Shabbat 68b that one can be obligated to bring a sacrifice if one knew it was Shabbat and that the action was forbidden, but did not know that one is obligated to bring a sacrifice. But, then the Gemara explains that even the rabbis would agree by oaths as it is a unique halakha, as usually one is only obligated in oath for a prohibition punishable by karet.
Shmuel rules that one is only obligated for an oath of expression that is expressed in words, not one that is in one's heart. Two sources are brought to raise a difficulty on Shmuel's position, but are resolved.