The final perek (=chapter) of Masechet Shevu’ot begins on today’s daf (=page). Perek Arba’ah Shomerim focuses on the oaths required by the Torah when someone is holding someone else’s property, either because he was watching it for him or because he had permission to use it.
According to the Torah (Shemot 22:6-12), the level of responsibility for which a shomer – someone who accepts responsibility to guard his friend’s object – is liable, depends on the personal gain that the shomer receives. The Mishnahon our daf (=page) enumerates four types of shomrim and their level of responsibility. They include:
A shomer hinam – who does not derive any personal gain or benefit from watching the object. In the event that the shomer hinam performs his duty responsibly and the object is lost or stolen, he can take an oath that he guarded it properly and he will be free of any further responsibility (see Shemot 22:6-7).
A sho’el – who borrows the object for his own use, without payment. He is responsible for anything that happens to the animal, and will have to pay full restitution to the owner (see Shemot 22:13). Only if the animal died in the course of normal work will he be free of responsibility to pay, if he takes an oath that that is what happened.
A shomer sakhar – who gets paid for watching the object, and
A sokher – who pays rent to use the object.
According to the tanna of our Mishnah, in these last two cases the shomer will be responsible if the object is lost or stolen, but not if an ones – an unexpected accident – takes place. The Torah’s examples of ones are if the animal dies, breaks a leg or is taken captive, and if the shomer sakhar or sokher takes an oath to that effect, they will not have to pay.
The case of sokher does not appear in the Torah, and the Gemara presents a disagreement between the tanna’im as to whether he is similar to a shomer sakhar as appears in the Mishnah, or to a shomer hinam.
The laws of the four shomrim are discussed at length in Masechet Bava Metzia and they are mentioned here in the context of explaining their obligations regarding the oaths that they must take.