Commentary for Bava Kamma 12:14
ור' ישמעאל אכל שמינה משלם שמינה אכל כחושה משלם שמינה
Would R. Ishmael maintain that the defendant, whether damaging the best or worst, is to pay for the best? — R. Idi b. Abin said: This is so where he damaged one of several furrows and it could not be ascertained whether the furrow he damaged was the worst or the best, in which case he must pay for the best. Raba, however, [demurred] saying: Since where we do know that he damaged the worst, he would only have to pay for the worst, now that we do not know whether the furrow damaged was the best or the worst, why pay for the best? It is the plaintiff who has the onus of proving his case by evidence. R. Aha b. Jacob therefore explained: We are dealing here with a case where the best of the plaintiff's estate equals in quality the worst of that of the defendant;<span class="x" onmousemove="('comment',' The amount of damages, however, would never be more than could be proved to have been actually sustained. ');"><sup>11</sup></span>
Tosafot on Bava Kamma
This means: It is perfectly sensible that if an ox consumed a bountiful plot he pays for a bountiful plot, but if he consumed a meager plot why should he pay for a bountiful one?
In this context the sentence “he consumed a bountiful plot, he pays for a bountiful one” is used only as an introduction to the question. Tosafot offers a second explanation, in which this sentence is a point of reference: i.e. since the first statement is obviously true, we must therefore question the truth of R’ Yishmo’ail’s ruling that when he ate a meager plot he must pay for a bountiful plot.
Alternatively, its meaning is as follows: since when an ox consumes a bountiful plot his owner pays only for a bountiful plot, and we do not impose a fine on him to pay more than he damaged, if so, when he consumed a meager plot, we should also not impose a fine on his owner to pay more than he damaged and require of him to pay for a bountiful plot.
The Gemara’s question assumes that according to R’ Yishmo’ail one has to pay more than he damaged. The Gemara does not entertain that idea according to R’ Akiva.
And if you ask: Why is the Gemara more prone to err about the statement of R’ Yishmo’ail, thinking that he means that if an ox ate a meager plot his owner must pay for a bountiful one, more so than in the statement of R’ Akiva. Perhaps R’ Akiva is also saying that if an ox consumed a meager plot his owner must pay with the most bountiful of plots in his fields.
And we can answer: That the reason that he was more prone to err in the words of R’ Yishmo’ail is because of how R’ Akiva’s response is phrased. R’ Akiva says; the verse comes only to teach that the victim collects from the choicest. Use of the word only implies that R’ Akiva heard from R’ Yishmo’ail that the verse comes to obligate the damager for more than he damaged. For example, if the ox consumed a meager plot, the ox owner must pay for a bountiful plot. Based on this understanding the Gemara questioned the view of R’ Yishmo’ail until it clarified his position.