Section 406. Any person who, through an act of performance made by another person or in any other manner, obtains something to the prejudice of such other person without legal ground, must return it to the latter. The acknowledgment of the existence or non-existence of a debt is deemed to be an act of performance.
The same provision shall apply if something has been obtained on account of a cause which has not been realized or of a ceased to exist.
Section 407. A person who has freely done an act as if in performance of an obligation, knowing that he was not bound to effect the performance, is not entitled to restitution.
Section 408. The following persons are not entitled to restitution:
A person who performs an obligation subject to a time clause before the time has arrived
A person who performs an obligation which has been barred by prescription
A person who performs an obligation in compliance with a moral duty or with the requirements of social propriety.
Section 409. When a person who is not a debtor has performed an obligation by mistake and the creditor, in consequence thereof, has in good faith destroyed or obliterated the documentary evidence of the obligation or given up any security or lost his right by prescription, the creditor is not bound to make restitution.
The provisions of the foregoing paragraph do not prevent the person who has performed from exercising a right of recourse against the debtor and his surety, if any
Section 410. A person who had made a performance for an intended result which is not produced is not entitled to restitution, if, from the beginning, it was known to him that the production of the result was impossible or if he was prevented the result in violation of good faith.
Section 411. A person who has made an act of performance, the purpose of which is contrary to legal prohibition or good morals, cannot claim restitution.
Section 412. If the property which was unduly received is a sum of money, restitution must be made in full, unless the person who received it was in good faith in which case he is only bound to return such part of his enrichment as still exists at the time when restitution is demanded.
Section 413. When the property which must be returned is other than a sum of money and the person who received it was in good faith, such person is only bound to return it in such condition as it is and is not responsible for less or damage to such thing, but he must return whatever he has acquired as compensation for such loss or damage. If the person who received the property was in bad faith he is fully responsible for the loss or damage even caused by force majeur, unless he proves that the loss or damage would have happened in any case.
Section 414. If restitution is impossible on account of the nature of the property received or for any other reason, and the person who received the property was in good faith, such person is bound only to return such part of his enrichment as still exists at the time when restitution is demanded.
If a person who received the property was in bad faith, he is bound to pay the full value of the property.
Section 415. A person who has received the property in good faith acquires the fruits thereon as long as such good faith continues.
In case where he has to return such thing, he is deemed to be in bad faith from the time when restitution is demanded.
Section 416. Expenses which were necessary for the preservation of the property or for its maintenance or repair must be reimbursed in full to the person who returns such property.
However such person cannot claim reimbursement of the ordinary expenses for maintenance, repairs or charges made within the ime during which he has acquired the fruits.
Section 417. For expenses other than those provided in paragraph 1 of the foregoing section the person who returns the property can claim reimbursement only if they were made while he was in good faith and if the value of the property is increased by such expenses at the time of restitution, and only to the extent of such increase.
The provisions of Section 415 paragraph 2 apply correspondingly.
Section 418. If the person who has in bad faith unduly received a property has made alternations in, or additions to it, he must return the property after having put it in its former condition at his own expense, unless the owner of the property chooses to have it returned in its present condition, in which case the owner must pay at his option either the cost of alterations or additions, or a sum representing the increased value of the property.
When restitution is to be made, if it is impossible to put it in its former condition or the property would be damaged thereby, the person who received the property must return it in such condition as it is and he is not entitled to compensation for any increase of value accruing to the property from such alterations or additions.
Section 419. No action on account of undue enrichment can be entered later than one year from the time when the injured party became aware of his right to restitution or later than 10 years from the time when the right accrued.