The law of *obligations deals with obligations arising from both contract and tort, i.e., those undertaken by the party or parties concerned of their own free will and those imposed by law on a person – against his will – in consequence of damage resulting from an act or omission on his part. There is a further group of cases which fall under a branch of the law known as unjust enrichment and relate to a person's liability which arises neither from his undertaking nor delictual act, but from the fact that he has derived a benefit to which he is not entitled, at the expense of another.
A general exemplification of this class of obligations in Jewish law is the discussion in the Mishnah of the matter of a person who hires from his neighbor a cow, which dies of natural causes after the hirer has lent it to a third party (BM 3:2). One opinion is that the hirer is not liable to the owner for the value of the cow – since the death of the cow is attributable to *ones and the hirer has no liability for loss resulting there from – but the borrower must compensate the hirer (i.e., the person from whom he received the animal) – since the borrower is liable for loss resulting from ones (see *Shomerim). However, R. Yose differs, questioning the hirer's right to "traffic with his neighbor's cow," i.e., it is inconceivable that the hirer shall enrich himself at the expense of the owner of the cow, who is the real loser, without any color of right thereto, and the hirer must therefore restore to the owner the value of the cow received from the borrower. R. Yose's opinion was accepted as halakhah (BM 36b; Yad, Sekhirut 1:6; Sh. Ar., ḤM 307:5). The same principle is enunciated by R. Johanan: "it is forbidden for a person to benefit [without authority] from another's property" (BM 117b), and the halakhah was decided as follows: "similarly, whenever a person performs an act or benefit in favor of another, the latter may not say, 'you have acted for me gratis since I did not authorize you' but he must give such person his reward" (Rema, ḤM 264:4; see also Ran on Rif, Ket. 107b). The problems of unjust enrichment are treated in Jewish law under the following five headings: (1) rescue of another's life; (2) rescue of another's property; (3) payment of another's debt; (4) improvement of another's property; (5) deriving benefit from another's property.
Rescue of Another's Life
The duty to rescue the life of another when endangered is enjoined in the Pentateuch: "Thou shalt not stand idly by the blood of thy neighbor" (Lev. 19:16). This duty includes the obligation to hire other persons against payment in order to rescue the person in danger (Sanh. 73a), who must refund to his rescuer all the expenses thus incurred by the latter: "For it is not a person's duty to save the life of his fellow with his own money when the person saved has money" (Piskei ha-Rosh 8:2; Sanh. 73a; Sh. Ar., ḤM 426:1, Sma and Siftei Kohen ad loc.). It was likewise decided that the heirs of the deceased must refund the expenses incurred by a third person in connection with the medical treatment of the deceased, even if not expended at the latter's request, since a person who of his own accord seeks a cure for the sick must not lose inasmuch as it is a matter of pikku'aḥ nefesh ("saving life") and whoever hurries to do so is praised (Resp. Rosh no. 85:2). This too is the law as regards the rescue and ransom of a Jewish prisoner in the hands of a gentile, and the latter – if he has the means thereto – must refund the ransom money to his rescuer (Rema, YD 252:12), since it is inconceivable that such a person "shall enrich his children while being a burden on the community" (Resp. Maharam of Rothenburg, ed. Cremona, no. 32; Mordekhai BM sec. 59).
Rescue of Another's Property
Under this heading are included cases in which a person knowingly, and without being requested to do so, acts to the benefit of another in a manner whereby the rescuer does not add to the other anything he did not have before but prevents the latter from suffering pecuniary loss. The basic laws concerning the duty to rescue another's property are expressed in two pentateuchal enjoinders, relating respectively to the duty of restoring lost property (Ex. 23:4; Deut. 22:1–3) and that of releasing an animal lying under its burden (Ex. 23:5; Deut. 22:4). In both cases the duty carries no return consideration (as regards restoring lost property, see Sh. Ar., ḤM 265:1; as regards releasing an animal, see BM 32a; Yad, Roẓe'aḥ 13:7; Sh. Ar., ḤM 272:6). However, the duty to provide aid gratuitously exists only as long as the rescue activities cause no loss to the rescuing party, but when he is likely to suffer loss there from he will not be obliged to act gratuitously (BM 2:9; Yad, Gezelah 12:4; Sh. Ar., ḤM 265:1; Tur. ḤM 272:2). The result is that even
As regards the duty to compensate the rescuer for a loss he has suffered, a distinction is drawn as illustrated in the following two examples. The Mishnah mentions the case where one person has a jar of wine and another a jar of honey; because of a crack in the honey jar, the owner of the other jar spills his wine and rescues the honey by pouring it into his own jar (the honey being the more expensive) and the Mishnah holds the latter is entitled "to his remuneration [sekharo] alone" (BK 10:4, and the further example there cited). According to this Mishnah the beneficiary has to remunerate the rescuer for his efforts alone and is not obliged to refund the latter the cost of his wine. On the other hand, in the Talmud in like circumstances it is stated in the name of R. Ishmael, the son of R. Johanan b. Beroka, that the person pouring out the wine "receives his wine out of the honey of his fellow" (BK 81b; 114b), i.e., that the owner of the wine is entitled to payment of the value of the wine spilled in order to rescue his fellow's honey. The contradiction between the two cases was reconciled on the basis that in the former case the owner of the rescued property was present at the place and time of the rescue but the rescuer, not having sought express consent for his action, is not entitled to a full refund of his expenses or the value of his wine, but only to his remuneration; in the latter case, however, the owner of the rescued property was not present as aforementioned and therefore the rescuer is entitled to a full refund of his expenses (for an explanation of this distinction, see Tos. BM 31b; Piskei ha-Rosh BM no. 28; Mordekhai BK no. 57).
In contrast to the above cases, the Talmud quotes the case of rescue of another's property (mavri'aḥ ari – one who chases away a lion from another's property) without the knowledge of the beneficiary, in which the latter is exempt from making any payment whatever to the rescuer (Ned. 33a; BK 58a; BB 53a). The Talmud mentions two elements which characterize the category of mavri'aḥ ari cases in which the rescuer is not entitled to remuneration. First, that the rescuer acted as he did of his own initiative; secondly, that he suffered no loss whatever as a result of such action. Some of the rishonim were of the opinion that this category of mavri'aḥ ari includes only those cases in which both the above elements operate and that the absence of one of them renders the beneficiary liable to payment for the benefit derived by himself (Tos. Ket. 107b; Mordekhai BK no. 57). Others held that this category includes also cases in which only one of the two elements is present and that there is no need for both to operate together (Tos. BK 58a; Rosh, loc. cit.). The rishonim added a further requisite for the beneficiary's exemption from payment in mavri'aḥ ari cases, namely, that the loss which the rescuer sought to avoid was of doubtful contingency. That is, when it may reasonably be accepted that even without the rescuer's intervention no loss would have occurred, as for instance in the case where the lion was far from the beneficiary's herd. Hence the rescuer will be entitled to payment of his remuneration if the beneficiary, but for the intervention of the former, was certain to have suffered loss (Tos. BK 58a; Rosh and Mordekhai, loc. cit.). Yet another material requirement (for the beneficiary's exemption from liability) is that the rescuer's action was not calculated to enrich the beneficiary in any way but merely to have prevented him loss (Tos. Ket. 107b; Tos. BK 58a).
Payment of Another's Debt
This question is discussed in the Mishnah (Ket. 13:2) in relation to the obligation of maintenance, in the case of a person who supports a wife whose husband has gone abroad – without being requested to do so by either the wife or her husband. Some of the tannaim hold the benefactor to have "put his money on the horn of a deer" and to have no claim, neither against the wife nor her husband, since he acted as he did of his own accord. Other tannaim take the view that the benefactor may deliver an oath as to the exact amount expended on the wife and recover this amount from her husband. The halakhah was decided according to the former opinion (Yad, Ishut 12:19; Sh. Ar., EH 70:8).
As regards debts arising from other causes, there is a difference of opinion among the scholars. In the Jerusalem Talmud (Ket. 13:2; 35d) two opinions are quoted. One is that the dispute concerning a debt for maintenance extends also to the case of any other regular debt paid on behalf of another and without the latter's knowledge; the other opinion is that the dispute relates solely to payment of a debt owed by the husband for the maintenance of his wife, but with regard to a regular debt paid on behalf of the debtor, the opinion of all is that it may not be reclaimed from the debtor since it cannot be said that the latter received an absolute benefit because of the possibility that his creditor may have granted a waiver of the debt, and therefore the person who has paid it is in the position of a mavri'aḥ ari (see above). From the Babylonian Talmud (Ned. 33a–b; Ket. 108a) it may be concluded, according to most of the commentators, that the dispute relating to a maintenance debt extends also to regular debts. Some of the commentators (R. Hananel and R. Tam) interpreted the statements in the Babylonian Talmud to mean that a debt not arising from maintenance and paid by another may, in the opinion of all, be reclaimed from the debtor because of the certainty of the benefit caused the latter (Tos. Ket. 108a). The majority opinion of the posekim is that a person who has paid another's debt of any kind whatever may not recover payment from
Improvement of Another's Property
This category includes cases in which a person knowingly, and without being requested thereto, acts so as to confer an actual benefit on another by affording him a gain or increment which he did not previously have. The classic example is the case of a person who "goes down" to another's property to plant it or erect a building thereon, without any request from the owner to do the work or undertaking on his part to pay for it (analagous to the Roman law negotiorum gestio). Thus, for instance, if a hired worker should work in the field of a third party, whether in error or because he was directed thereto by his employer, the owner of the field will have to pay for the benefit derived, even though he did not request the work, for otherwise he will be in the position of having been enriched without right at another's expense (Tosef. BM 7:7; BM 76a).
In the case where a person plants another's land without permission, Rav's opinion is that "an assessment is made and he is at a disadvantage," whereas Samuel holds, "an estimate is made of what a person would pay to plant such a field." In the Talmud it is stated that there is no dispute between Rav and Samuel but that Rav refers to a field which is unsuitable for that which has been planted thereon, while Samuel refers to a field which is suitable for such planting (BM 101a). The scholars disputed the meaning of the expression "an assessment is made and he is at a disadvantage." R. Hai Gaon (Sefer ha-Mikkaḥ ve-ha-Mimkar, 7:33) and R. Zerahiah ha-Levi (Ha-Ma'or ha-Gadol to Rif BM 101a) held it to mean that the planter is only entitled to payment on the basis of the lowest price at which cheap workers can be hired to execute the same work; according to Rashi (BM 101a), Rosh (ad loc.), and others, the expression means that if the planter's expenses exceed the gain derived by the owner of the field then the former is only entitled to the value of such gain, but if the other way round then the planter is only entitled to the sum of his expenses. The halakhah was decided that a person who plants another's field without permission is at a disadvantage when the field is unsuitable for such planting, but if it is so suitable an estimate is made of how much one would be prepared to pay for planning that field (Yad, Gezelah 10:4).
Another example is the case where a person whose property surrounds the property of another on all sides fences the interior borders of his property, thereby enclosing at the same time also the surrounded property – without the authority of its owner. In the Mishnah (BB 1:3) there is a difference of opinion as regards the measure of liability of the owner of the surrounded property to pay toward the cost of the fence by which he too is served, and in the Talmud these divided opinions are interpreted in various ways (BB 4b and Codes; Rashi BK 20b; Ha-Ma'or ha-Gadol (see above) to Rif BB 4b; cf. Tos. BK 20b; Maim., Comm. to BB 1; Yad Ramah BB 4b; Ramban, Nov. BB 4b; Milḥamot ha-Shem thereto, etc.). All opinions agree that the owner of the surrounded property has liability for payment toward the costs of the fence from which he benefits, even though he has neither requested its erection nor undertaken to bear the costs thereof; the dispute – even among the posekim – centers on the varying measure of his liability, according to the factual circumstances. Liability for payment derives from the consideration that the "enclosing owner" (the makkif) is caused special expenses by the surrounded property since it causes a lengthening of the boundaries of the surrounding property and because the owner of the surrounded property benefits without right on account of the special expenses caused to the other (see BK 20b; for a further example, see BK 9:4; BK 101a; Yad, Sekhirut 10:4; Sh. Ar., ḤM 306:3, 6).
The posekim did not fail to observe that the consequence of the above law was to submit everyone to the constant danger of being placed in the position where he might be caused a benefit from and become obligated to pay for expenses incurred by his fellow in which he is not at all interested. Hence it was decided that such a beneficiary was to be exempted from liability if he had declared in advance that he had no interest in the proposed benefit and was not prepared to make any payment whatever in connection therewith (Maggid Mishneh Shekhenim 3:3; Beit Yosef ḤM 155:13).
Deriving Benefit from Another's Property
This category includes the cases in which a person benefits without authority from another's property, the benefit taking the form of a saving of expenses or the prevention of harm. The classical case discussed in the Talmud is the matter of a person who lives on another's property without the latter's knowledge or consent (BK 20a). Four possibilities are discussed: (a) If the premises are anyhow not available for letting and, in addition thereto, it is clear that even without such premises the occupier, for whatever reason, would not have hired some other residence for himself, then the latter is absolved from payment; the explanation for this is that he has neither caused a loss to the owner of the premises nor enjoyed any benefit himself since a benefit is expressed in some measure of monetary gain – nonexistent in this case. (b) If the premises are for hire and the occupier, but for his occupation thereof, would have hired some other residence, he will be liable for payment since he has derived a benefit at the cost of the owner's loss. (c) If the premises are not for hire and the occupier, but for his occupation thereof, would have hired some other residence, he will be absolved from payment since the benefit he has derived is not at another's expense, the owner having lost nothing; however, if enjoyment of the benefit should involve any measure of loss to the owner, the benefit will be at another's expense and the occupier liable for the full value of his benefit (BK 20a–b; Yad, Gezelah 3:9; Sh. Ar., ḤM 363:6–7). (d) Opinions are divided as regards the case where the premises are for hire but the occupier, even without his occupation thereof, would not hire other premises. Some of the rishonim held that the occupier, because he
A person who benefits unawares must pay for the benefit. The laws of *tort prescribe that the owner of an animal is absolved from paying for the produce of another which the animal has eaten up while grazing in a public domain; however, "if you have benefited, you must pay for the benefit" (BK 2:2), i.e., if the owner should derive benefit from the fact that his animal has fed in the aforementioned manner (by saving himself the cost of the animal's feed for that day), he will be liable to the owner of the devoured produce for the value of the benefit, lest he enjoy an undue gain at another's expense (BK 20a and Codes, Nimmukei Yosef thereto, TJ, BK 2:4, 3a; see also the difference of opinion there quoted concerning the manner of assessing the value of the benefit; for a further illustration of this class of case, see BK 6:2).
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