Question: How does R. Yishmael expound [that it is only for the future]?

Answer #1: "Oh Nefesh Ki Sishava Levatei bi'Sefasayim" is a Klal (general term). "Lehara Oh Leheitiv" is a Prat (specific term. When there is) a Klal u'Ferat, the Klal consists only of the Prat [matters of the future].

Objection: The Prat is only matters that have harm and benefit!

Answer #2: "Lehara Oh Leheitiv" is a Prat. "L'Chol Asher Yevatei" is a Klal.

Objection: [When there is] a Prat u'Chlal, everything is included in the Klal. This includes matters of the past!

Answer #3: "Oh Nefesh Ki Sishava Levatei bi'Sefasayim" is a Klal. "Lehara Oh Leheitiv" is a Prat. "L'Chol Asher Yevatei" is another Klal. [When there is] a Klal u'Ferat u'Chlal, we include matters similar to the Prat (matters of the future).

Question [R. Akiva]: Just like the Prat is explicit, matters with Hara'ah or Hatavah [so you should include only such matters]. What is [your] source for matters without Hara'ah or Hatavah?

Answer [R. Yishmael]: The Torah includes this ("l'Chol Asher Yivatei").

Question [R. Akiva]: If the Torah includes for this, it includes also for this (oaths about the past)!

(R. Heila citing R. Lazar): So R. Yishmael answered R. Akiva. Do we find things for which b'Mezid one is liable due to Shevu'as Sheker, and b'Helam due to Shevu'as Bituy?! (According to you, we do - Shevu'as Bituy of the past!)

R. Akiva [to R. Yishmael]: Do you not include matters without Hara'ah or Hatavah, and they are not written?! (Likewise, we include matters of the past!)

[R. Yishmael: Even though I include matters without Hara'ah or Hatavah, which are not written, they have [the same Lav "Lo Yachel Devaro" that applies to matters] of Hara'ah and Hatavah! However, matters of the past [there is no Lav for them].

[R. Akiva]: If the Torah includes for this, it includes also for this (oaths about the past)!