After having enumerated the different kinds of contracts, let Us consider those obligations which are not understood to properly arise from contracts, but, nevertheless, because they do not partake of the nature of an illegal act are considered to arise "as it were from a contract".

(1) Therefore, whenever anyone attends to the affairs of another while he is absent, rights of action reciprocally arise between them which are designated those of "business transacted"; but a direct action lies in favor of the owner of the matter in question as against the party who transacted the business; and a contrary action also lies in favor of the latter. It is evident that, properly speaking, these do not arise from any contract, since actions of this kind can be instituted when anyone has meddled with the affairs of another without authority, and for this reason those whose business has been transacted are made liable without being aware of the fact.

This rule has been adopted for public convenience, so that when persons are compelled by some sudden emergency to travel in foreign countries — no one being entrusted with the transaction of their business during their absence — their affairs may not be neglected; for certainly no one would take charge of them if he did not have any right of action to recover what he had expended for that purpose. But just as he who has transacted the business of another advantageously places the owner of the same under an obligation; so, on the other hand, he also is bound to render an account of his administration; and in this instance he is alleged to render it in compliance with requirements of the most exact diligence, nor will it be sufficient for him to have employed the same diligence which he is accustomed to make use of in his own business, if someone else who was more prudent could have discharged his duties in a better manner.

(2) Guardians, also, who are liable to an action of guardianship cannot properly be understood to be bound by a contract, for no contract exists between a guardian and a ward; but for the reason that they are evidently not liable on account of criminality, they are considered to be so upon a quasi-contract. In this instance, likewise the actions are reciprocal; for not only is the ward entitled to an action of guardianship against his guardian, but, on the other hand, the guardian has a contrary action of guardianship against the ward, either when he has expended anything for the benefit of the latter, or has become liable for him, or has encumbered his own property to his creditor.

(3) Moreover, where property is held in common by several persons and no partnership exists; for example, where it has been bequeathed or given to them jointly, and one of them is liable to the other in an action for a division of property held in common because he alone has collected the crops from said property, or because his associate alone has incurred necessary expenses for the benefit of the same; he is not, strictly speaking, considered to be bound by a contract, (since no agreement was entered into by them) but as he is not liable for any illegal act, he is considered to be bound by a quasi-contract.

(4) The same principle applies with reference to a party who is liable to his co-heir in an action for partition of the estate.

(5) The heir, also, is not actually liable upon a contract for the payment of legacies (as it cannot properly be said that the legatee has transacted any business with either the heir or the deceased) and still, for the reason that the heir is not liable on account of a criminal act, he is considered to be indebted under a quasi-contract.

(6) Moreover, he to whom another by mistake pays a debt which he does not owe is held to be liable under a quasi-contract, for to such an extent is he not properly to be considered bound under a contract, that if we examine the genuine reason, he may be said, as We stated above, to be liable through the dissolution rather than through the making of a contract, for he who pays money with the intention of discharging a debt appears rather to pay it in order to terminate a contract than to enter into one; nevertheless, the party who receives the money is bound just as if it had been loaned to him for consumption, and therefore is liable in a personal action for recovery.

(7) In some instances, however, where a debt which is not due is paid by mistake there can be no recovery; for, the ancients declared that in every case where the sum claimed in an action was increased by denial, there could be no recovery where money was paid which was not due; as, for example, under the Lex Aquilia, or in actions for a legacy.

The ancients, however, intended this principle only to be applicable to such legacies as were expressed in definite terms, and were bequeathed to anyone by condemnation; but one of Our Constitutions has invested all legacies and trusts with a similar character, and has likewise extended this increase to all of them; but this was not done for the benefit of all legatees, but only with regard to such legacies and trusts as have been left to holy churches and other venerated places honored by the spirit of religion or piety, and if these are paid when they are not due they cannot be recovered.