On the (quasi) contractual nature of the solutio indebiti in the Institutes of Gaius

Abstract

In his Institutes, Gaius presents a summa divisio obligationum, which states that every obligation either arises from a contract or from an offence (Gai. 3,88). Hence, any lawful event giving rise to obligations is a contractus. This is so, in principle, regarding the payment of what is not due (solutio indebiti). However, after Gaius indicates that the receiver of what was not owed from a person who pays in error is obligued as the borrower (re obligatur), because for him the simple loan is considered a contract (Gai. 3,90), he cast doubts on the solutio indebiti, by pointing out that he who pays in error what was not owed, rather wishes to extinguish an obligation (distrahere) than to establish one (contrahere), so that in this particular case it seems to be of a kind not arising from a contract (Gai. 3,91). Gaius does not focus on the absence of conventio between the parties, but on the lack of intent to establish an obligation, which is not the same. Here lies the origin of a future category of quasicontracts in civil law tradition.