הלכות גזילה ואבידה

The following law applies when a powerful and violent gentile took over property belonging to a Jew by force, seizing his field because the owner owed him a debt, caused him damages or caused him financial loss. If, after taking possession of the field, the gentile sold it to another Jew, the owner cannot expropriate it from the purchaser.

When does the above apply? When the owner admits that the gentile who sold the property told the truth, or when two Jewish witnesses substantiate the truth of the gentile's claims.
Similarly, if there was a king or a ruler in that locale who could summon the gentile to court, and the owner did not lodge a claim against him, he cannot expropriate the property from the person who purchased it from the gentile. This applies even though the owner does not admit the truth of the gentile's claim, and even though there are no witnesses that the gentile told the truth. For the purchaser can tell the owner: "If the gentile is a robber, why did you not sue him according to the laws of the land?"

The following laws apply with regard to gentiles who oppress the Jewish people and seek to kill them, unless they ransom themselves from the gentiles by ceding title to a field or a home, and giving it to the gentiles in return for their release.
When the oppressor desires to sell this land and the owner has the means to purchase the property, he is given priority over all others. If the owner does not have the means to purchase the property, or the property has remained in the possession of the oppressor for more than twelve months, whoever comes first and purchases the property from the oppressor acquires it.
The purchaser must, however, give the original owner a fourth of the land or a third of the funds. For the oppressor sells the land cheaply; since the land is not his, he will sell it for approximately a fourth less than its value. This portion belongs to the original owner, because the reason it was sold cheaply was that it belonged to him.
Therefore, a person who acquires it from the oppressor for 30 zuz must pay 10 to the original owner or give him one fourth of the land. If this is done, the purchaser acquires full title to the land. If he fails to do this, the quarter of the land is considered to be property obtained by robbery.

The following rules apply if a squatter enters a field belonging to a colleague without permission and plants trees there. If the field was one appropriate for trees to be planted, we evaluate how much a person would be willing to pay for trees to be planted in this field, and he collects this amount from the owner of the field. If this field is not suitable for planting, the squatter's improvement of the field should be evaluated, and he is judged at a disadvantage.

Courtyards are considered to be appropriate for construction and to add homes and lofts. Therefore, the geonim ruled that a squatter who builds in a colleague's courtyard without his consent is regarded like a person who plants trees in a field appropriate for planting. If the building is useful and is appropriate for that courtyard according to the local custom, we evaluate how much a person would give to have such a building constructed and require the owner to pay that sum to the squatter.

When a person enters a colleague's field with the latter's permission, his improvement of the field should be evaluated, and he should be given the advantage in evaluating the amount of money due him. This applies even if he planted trees in a field that was unfit for planting.
If his expenses exceed the field's increase in value, he is reimbursed for his expenses. If the field's increase in value exceeds his expenses, he is reimbursed for the field's increase in value.
A husband who tills property belonging to his wife, and a partner who tills a field in which he owns a share are considered to have been given permission to enter the land. Their improvement of the field should be evaluated and they should be given the advantage in evaluating the amount of money due them.

When a squatter enters a field belonging to a colleague without permission and plants trees or builds there and the owner of the field comes afterwards and completes the building or guards the trees planted, or performs any other activity that indicates that he is pleased with the squatter's activity and considers it desirable, the squatter's improvement of the field should be evaluated and he should be given the advantage in evaluating the amount of money due him.

When a squatter enters a ruined building belonging to a colleague and rebuilds it without permission, the improvement he has brought about should be evaluated, and he is judged at a disadvantage.
If the owner of the building says: "I am taking my stones and wood," his words are heeded with regard to a house,but this principle is not applied with regard to a field, for building and destroying a structure in a field weakens the fertility of the land.
If the owner of the land tells him: "Remove what you built,"his words are heeded.

Whenever the improvements a person brought about are evaluated - whether he is judged at an advantage or at a disadvantage - he is not entitled to collect any money unless he first takes an oath while holding a sacred object, with regard to the amount of his expenses.
If he says: "Let the judges come and evaluate the expenses. Whatever I spent is in the open. Let them evaluate the worth of the wood, the stones, the mortar, and the wages of the workers according to the lowest standards," his request is accepted, and he is entitled to collect his due without taking an oath. Similarly, if a person collects only the value of the improvement of the property, and he is judged at an advantage, he is not required to take an oath.

The following rule applies whenever the improvements a person made are to be evaluated and he is entitled to collect money, and the owner of the field claims to have paid him, and the person who tilled the field claims that he did not receive anything. The claim of the person who tilled the field is accepted. He must take an oath that he did not receive anything, and he is entitled to collect his due. For we tell the owner of the field: "An evaluation of what he is due was not made yet. Thus, you did not know how much you were obligated to give. How could you have paid him?"
A different rule applies, however, if the evaluation was already made and the owner of the field was told to pay a specific amount to the person who tilled it. If the owner of the field claims to have paid him, although the person who tilled the field has not taken an oath yet, the claim of the owner is accepted. The owner must take a Rabbinic oath that he paid, and then he is freed of liability. The rationale is that land is always considered to be in the domain of its rightful owner.