What is Isar? 'This loaf is forbidden to me like the day that father died, like the day that Ploni was killed, like the day that I saw Yerushalayim in ruins, this is Isar that the Torah said. (RASHBA 12a - he is Matfis in (forbids like) something forbidden only to himself.)

(R. Ba citing R. Yochanan, and Rav): This is if he had vowed [not to eat] on that day. (He forbids the loaf like something forbidden through a vow.)

Question (R. Yosi): If he had vowed about that day, why does he need 'Isar' (to say 'Asur like the day...')? He should say 'like that day'! (PNEI MOSHE)

(Beraisa): Isar (if one said 'this loaf is Isar, that I will not eat it'), this is [like] a Shevu'ah. Mivta (if one said 'this loaf is Mivta, that I will not eat it'), this is [like] a Shevu'ah.

If you say that Isar is a Shevu'ah, he is liable for each Isar and Isar, and for each Shevu'ah and Shevu'ah. If you say that Isar is not a kind of Shevu'ah, (if he forbade through Isar and also swore), he is liable for this (Isar) by itself and for this (Shevu'ah) by itself.

Question: [The Reisha said that] Isar is a Shevu'ah, and then it says 'if you say so...'?

Answer #1 (R. Elazar): Two Tana'im [taught the Reisha and Seifa. The first Tana was sure, and the second Tana was unsure.]

Answer #2 (R. Yirmeyah): [The entire Beraisa] is one Tana. If he said in an expression of Neder, you obligate him like for a Neder. If he said in an expression of Shevu'ah, you obligate him like for a Shevu'ah.

If he said 'Isar, it is Alai' (he forbade the object), you obligate him like for a Neder. If he said 'Isar, that I will not taste it' (he forbade himself), you obligate him in place of a Shevu'ah.

(Beraisa): If you say that Isar is a kind of Shevu'ah, he is liable for each Isar and Isar, and for each Shevu'ah and Shevu'ah.

(R. Yosi): This applies only with five loaves (he forbade one, and then forbade the second like the first...), but with one loaf, once he mentioned Shevu'ah about it, he made it like Neveilah. From now and onwards, he is like one who puts Shevu'os on Isurim, and Shevu'os do not take effect on Isurim.

(R. Chananyah): It is even with one loaf, like the following Beraisa;

(Beraisa): This is a stringency of [Shevu'os] about the past over the future. If he said (falsely swore) 'I did not eat it, I did not eat it', he is liable for each one. 'I will not eat it, I will not eat it', he is liable only once. (After the first, he is obligated to eat it, so additional Shevu'os do not take effect.)

(Beraisa): If you say that Isar is not a kind of Shevu'ah, he is liable for this (Isar) by itself and for this (Shevu'ah) by itself.