Bava Metzia, Chapter 6, Mishnah 8 - the final Mishnah of the chapter. The topic discussed in it: a person who serves as a messenger or waiter, who moves an object from place to place and drops it. Is he obligated to pay? And is there a difference between an unpaid watchman and a paid watchman?
The text of the Mishnah:
"Hamaavir chavis mimakom lemakom" - A person who moves a barrel from one point to another.
"Veshavrah" - The barrel fell from his hands and broke.
"Bein shomer chinam bein shomer sachar" - There is no practical difference whether a wage is paid for moving the object. A paid watchman is one who receives payment for his mission, and an unpaid watchman is one who does a favor for his friend and moves the object for him.
"Yishava" - An oath is sufficient for him. The simple assumption is that this refers to one of the three watchmen's oaths from the Torah: the watchman swears that he was not negligent in his guarding, and thereby is exempt.
Regarding this, "Rabbi Eliezer" wonders. It is worth noting that the correct version is likely Rabbi Elazar, since the Gemara explains that the Tanna Kamma is Rabbi Meir, and Rabbi Elazar heard the teaching from him. Rabbi Eliezer was the teacher of Rabbi Akiva, while Rabbi Meir was the student of Rabbi Akiva, and therefore it is unlikely that Rabbi Eliezer would quote Rabbi Meir. The reference, therefore, is to Rabbi Elazar ben Shammua.
And his wording: "Zeh vazeh yishava, vetame'ah ani im yachol zeh vazeh lishava" - I too have heard that these people swear, whether an unpaid watchman or a paid watchman, but I wonder and do not understand how they can swear this oath and be exempt.
The difficulty of Rabbi Elazar:
Let us start with a paid watchman, which is the middle category in terms of levels of obligation. He is exempt from unavoidable accidents, but is liable not only for negligence - like an unpaid watchman - but also for theft and loss, which are intermediate cases. That is to say, the object was lost or stolen, and even though he was not negligent in this, nevertheless had he been more careful and improved his guarding, it presumably would not have been lost or stolen.
The case before us is parallel to those intermediate cases: the person moved the barrel, and it is possible that he was not negligent - he did not act frivolously or irresponsibly - but had he been more careful, he almost certainly would not have broken it. Since extra caution would have prevented the damage, a paid watchman cannot be exempt with an oath that he was not negligent, since negligence is not the issue at all: even without negligence, the middle category makes him liable.
The same applies to an unpaid watchman. Although he is exempt from unavoidable accidents as long as he was not negligent, sometimes the accident itself is negligence: if the path was flat and he stumbled and fell, this is carelessness on his part, bordering on negligence, and even in such a case he does not deserve to be exempt. It turns out that the matter is not understood, and this is the wonderment of Rabbi Elazar.
The resolution of the Gemara - an enactment of the Sages:
The Gemara explains that indeed the matter is not understood, because this is not the intention of the Mishnah. It is true that they are not exempt with an oath that they were not negligent, for negligence is not the only issue, and sometimes even in a place where there is no negligence there is an obligation on an unpaid watchman, and certainly on a paid watchman.
Rather, here a rabbinic law is introduced: a special enactment of the Sages based on the enactment for workers. If we were to hold workers liable for every accident and breakage - a liability that by strict Torah law they are obligated in - no person would agree to serve as a messenger or waiter, since eventually a mishap would occur to him and he would be required to work a whole week to cover the cost of the damage. And since we need workers, the Sages enacted to exempt them from payment in a case where an accident occurred.
Therefore, the oath mentioned in the Mishnah is a Rabbinic oath, stating that he did not do so intentionally and did not mean to break it. If he broke it on purpose, he is certainly liable to pay; but if it happened by accident, the Sages exempt him. This is the practical halachah.
With this, with God's help, we conclude the sixth chapter of Bava Metzia. The next chapter is HaSocher Es HaPoalim.