Bava Kamma, Chapter 1, Mishnah 2 (Inspired by Rabbi Dovid Spetner). The Mishnah establishes several general principles regarding when a person is obligated to pay for damage caused by their property. The Mishnah opens: "Kol shechavti bishmirato hichsharti es nizko" - Anything I am obligated to guard, I have prepared its damage. The Mishnah uses the first person as a literary device, meaning: any property that I have a duty to guard and ensure does not cause harm, if I was negligent in guarding it, it is as if I myself prepared and orchestrated the damage, and I bear personal responsibility. In other words, whoever is obligated to guard, the blame rests on them.
Who is responsible for guarding:
It turns out that if a person owns a cow, but hired someone else to watch it, and the cow went out and trampled someone else's garden - the owner is not the responsible party, but rather the one who was entrusted to guard it. He is the one who was supposed to watch over it, and therefore the responsibility falls on him.
However, this is on the condition that the person appointed to be the responsible party is capable of it. Someone who lacks mental competence - a cheresh, shoteh, or katan (a deaf-mute, a mentally incompetent person, and a minor) - cannot be relied upon. Therefore, if someone appointed an eleven-year-old child to guard a pit or a cow, and the cow went out and caused damage - the child is not responsible, but rather the one who foolishly asked the child to watch the cow or the pit. The same law applies to a cheresh and a shoteh.
Not only that, but even if the cow is behind a closed fence and there is no reason for it to get out, and everything is secure - the moment someone says to a cheresh, shoteh, or katan, "Please watch the cow behind the fence," their very involvement makes the situation worse. After all, it is known what will happen: they will say, "Here is a cow, let's play with it," and they will open the gate. Thus, it is specifically by bringing the minor into the picture that the owner becomes liable, even though without him he would have been exempt, since the gate was properly closed. From the moment he involved the child as a watchman and supervisor over the animal, and the child opened the gate - the owner is liable. The same applies to a pit: there is a reasonable chance the child will uncover the covered pit, and similarly in other cases.
"Hichsharti bemiktzas nizko chavti betashlumin kehachsher kol nizko" - If I prepared part of its damage, I am obligated to pay as if I had prepared its entire damage:
Once again, the Mishnah uses the first person: if I prepared part of the damage potential of a thing, I am liable as if I had created the entire damage potential. As the Bartenura explains: a pit with a depth of nine tefachim is not considered a pit that causes death, and if an animal falls into it, there is no reason for it to die. If it does die - the digger is exempt, because it was not the pit that caused its death. A second person comes and deepens the pit to ten tefachim, thereby turning it into a pit that causes death, and now an animal falls in and dies. Who is responsible - the one who dug the first nine tefachim or the one who dug the tenth tefach? The Mishnah establishes that the one who dug the tenth tefach bears full responsibility, because he is the one who turned the pit into a pit that causes death.
This is how the Bartenura understands it, based on a ruling in accordance with Rabbi Yehuda in the Gemara, who argues with the Sages. According to Rabbi Yehuda, the liability applies specifically when a fundamental change is made to the source of damage - and in our case, the pit. At nine tefachim it is not a pit that causes death, and at ten it is a pit that causes death, and since the second person made it so, he bears full responsibility. However, according to Rabbi Yehuda, as the Bartenura learns, if the animal only broke its leg in the ten-tefach deep pit - both diggers, the one who dug the first nine tefachim and the one who dug the tenth tefach, are liable for the injured animal, since both contributed to its injury, and they share the responsibility.
The Sages disagree and hold that the second person who dug in the pit is fully liable for both the death and the injury, because he made the pit more dangerous. The Shulchan Aruch, and this is also brought in the Bartenura, rules like the Sages: the second person is liable in all cases, even if what he did did not constitute a qualitative and fundamental change in the nature of the dangerous object left in the public domain.
Which properties are included in the liability:
The Mishnah continues and lists the types of properties for which a person must pay compensation if their property damages them - because not all property is included in this, and there are exceptions:
"Nechasim she'ein bahem me'ilah" - Properties not subject to the laws of me'ilah. The damaged property must be property to which the laws of me'ilah do not apply. Me'ilah is the forbidden use of hekdesh, property belonging to the Beis Hamikdash. Therefore, one who damages property of the Beis Hamikdash that is subject to me'ilah does not pay damages. The basis for this law is in the verse: "If a man's ox gores his neighbor's ox" - for his neighbor's ox he is liable, but not for that of the Beis Hamikdash, which is not "his neighbor's".
Why did the Mishnah not use the term "hekdesh"? Because this Mishnah follows the view of Rav Yosef, who holds that not all hekdesh is subject to me'ilah, since kodashim kalim are considered the property of the owners. Thus, for certain types of hekdesh - such as kodashim kalim or an invalidated sacrifice, which are not subject to me'ilah - one who damages them is liable to pay.
"Nechasim shel bnei bris" - Properties of members of the covenant. The damaged property must be owned by a Jew, for if it is not owned by a Jew, there is no Torah obligation to pay. In the opposite case - a non-Jewish neighbor whose cow went out and damaged a Jew's property - the Beis Din in the Land of Israel will enforce payment, since it involves Jewish property, based on those same Talmudic discussions.
"Nechasim hameyuchadim" - Designated properties. Private property, excluding hefker, which is public property with no owner. For example: a wild ownerless cow running around and goring a person's horse - no compensation is paid to the horse's owner.
At first glance, what would we have thought? After all, an ownerless cow has no owner, so whom will the horse's owner bring to Beis Din to pay him? Rather, that is not the point. The novel ruling is that even if a person subsequently comes and acquires the cow for himself, saying, "It is an ownerless cow and I will acquire it," the injured horse's owner cannot sue the one who just now acquired it.
Why would there be room to think otherwise and impose responsibility on the acquirer? Because the rule is that a goring cow has the status of a tam, a docile cow, and most cows are considered docile unless they have been established as dangerous, and the payment is chatzi nezek - compensation for half the damage caused. Additionally, there is a kind of limited liability, and the maximum payment transferred to the injured party is the total value of the cow. This implies that under normal circumstances, someone whose property was damaged by a cow could have seized the cow as collateral and collected the payment from the cow itself. Therefore, one might have thought that the injured party - the horse's owner in the example - has a justified claim to that cow, and when someone comes to acquire it from the ownerless property, the horse's owner would say to him, "This cow is already mine, since it belongs to me on account of the damage it caused." The answer is that this is not the case.
The Gemara brings another example for "nechasim hameyuchadim", that only private property is included in the liability: a person who had a cow and declared it ownerless, and before being brought to Beis Din he is once again no longer its owner - he is exempt, also based on the Talmudic discussion. However, if he reacquires his cow, he will once again become liable.
"Uvechol makom chutz mirshus hameyuchedes lamazik urshus hanizak vehamazik" - And in any place except a domain designated for the damager, and a domain belonging to the injured party and the damager:
Generally, the obligation to compensate in a case where a person's property caused damage applies wherever the damage occurred: if a person's dog bit his friend's cow, he is liable to pay. But the exception is a domain designated for the damager: a cow that entered a person's courtyard, a place where it had no permission to be, and the dog of the courtyard's owner bit it - the problem lies with the cow's owner, who had no permission whatsoever to bring it into his friend's courtyard.
All this is based on the assumption that it is indeed a domain designated for the damager, meaning the private domain of the one who caused the damage - the owner of the damaging property - and the reason for the exemption stems specifically from the fact that the injured party, or his damaged property, had no permission to be there. Therefore, if a person invited his friend and his cow into his domain, and when the cow entered, his dog bit it - he is liable, since he invited them to enter, even though this occurred in his private domain.
It is also worth noting that the rule according to which a person is exempt when the damage occurs in his private domain deals specifically with damage caused by his property, such as if his dog bit a person or an animal that had no permission to be there. However, if the person himself caused the damage - he and not his property - he is liable, for he has no right to injure his friend or his animal simply because they are in his domain.
And similarly, "urshus hanizak vehamazik" - a domain belonging to the injured party and the damager. In a jointly owned area there is also an exemption, but it is more limited, and refers specifically to damages of Shen and Regel. If there are two partners in a field, and both are permitted to bring their cows there, and one of them also brought his potted plant into the field, and his friend's cow knocked over the potted plant and broke it - he has no claim against him. This is a case of Regel, cows knocking things over, and the injured party cannot sue, since the cow has a right to be there in their jointly owned field.
Here too, this is based on the assumption that both had permission to be there. But two partners in a china shop, where it is obvious that bulls should not be brought in - if one of them brought his bull into the shop and the bull knocked things over, he is liable to his friend, even though the shop is jointly owned. The ownership over it was intended for keeping china and objects, not for keeping animals, and therefore there is no permission to bring the cow in there, and when it knocks things over - this is again damage of Regel, and he must pay compensation.
"Ucheshehizik chav hamazik leshalem tashlumei nezek bemeitav ha'aretz" - And when it causes damage, the damager is obligated to pay damages from the best of the land:
In a case where a person's property did indeed cause damage, the owner responsible for guarding it is obligated to pay compensation from his best properties. This is essentially the same law we learned in the previous Mishnah: if the damager - the one who caused the damage or is responsible for it - pays using land, he must pay from his best lands; however, he is permitted to pay with cash or other movable property, which are always considered the best.
And if you will say: why does the Mishnah repeat this law? One explanation is that if we learned the previous Mishnah according to the view of Shmuel, as the Bartenura explained, that only four of the six categories were listed there - Shen, Regel, Esh, and Bor - while Keren was not included in the first Mishnah, because with Keren the payment is usually only chatzi nezek. Therefore, the Mishnah here comes to teach us that even for damages of Keren, where the laws are different and the animal intends to cause damage, when paying with property - the payment is from the best of the properties.
In summary: In this Mishnah we learned the principles of liability in damages: the one obligated to guard is the one who bears responsibility (and appointing a cheresh, shoteh, or katan to guard makes the appointer liable); one who prepares part of the damage is liable as if he prepared it entirely, like a pit that was deepened to ten tefachim; the liability is limited to properties not subject to me'ilah, properties of members of the covenant, and designated properties; the exemption in a domain designated for the damager, and in a domain belonging to both the injured party and the damager for damages of Shen and Regel; and the obligation to pay from the best of the land, which applies even to damages of Keren.