Sources Obligations arising out of the will of the parties are called
voluntary, and those imposed by operation of law are called
involuntary. Sometimes these are called conventional and obediential. The events giving rise to obligations may be further distinguished into specified categories. • voluntary: • unilateral promise (
pollicitatio) – undertaking by promisor only to perform, not requiring the promisee's agreement • contract •
quasi-contract •
negotiorum gestio – duty to repay an intervenor (
gestor) who has managed the affairs or property of another (
dominus negotii) who was unable to so •
solutio indebiti – undue payment or delivery of a thing to another (
accipiens), who is then obligated to return the thing to the payer (
solvens) • involuntary: • delicts and quasi-delicts (equivalent to the
common-law tort). •
unjust enrichment (
condictio indebiti) One of the first known classifications was made by
Gaius in his
Institutes, who divided obligations into obligations
ex contractu (obligations arising from agreements) and obligations
ex delicto (obligations arising from
civil wrongs and crimes). However, since this dichotomy was too simplistic, in his later work
Res cottidianae Gaius classified all obligations into the aforementioned obligations
ex contractu, obligations
ex delicto, and obligations
ex variis causarum figuris, which was a
heterogeneous category that was supposed to include all the cases of obligations not arising from torts or contracts. The most precise Roman classification of obligations was featured in
Justinian's Institutes (not to be confused by Gaius'
Institutes), which classified them as obligations arising from contracts (
ex contractu), those arising from torts (
ex maleficio), those arising from quasi-contracts (
quasi ex contractu), and those arising from quasi-delicts (
quasi ex maleficio).
Contracts A contract can be broadly defined as an agreement that is enforceable at law.
Gaius classified contracts into four categories which are: contracts
consensu, verbal contracts, contracts
re, and contracts
litteris. But this classification cannot cover all the contracts, such as pacts and innominate contracts; thus, it is no longer used. According to many modern legal scholars, the most important classification of contracts is that of contracts
consensu, which only require the consent of wills to create obligations, and formal contracts, which have to be concluded in a specific form in order to be valid (for example, in many European countries a contract regulating the purchase of
real estate must be concluded in a special written form that is validated by a
public notary).
Delicts Quasi-contracts Quasi-contracts are supposed to be sources of obligations very similar to contracts, but the main difference is that they are not created by an agreement of wills. The main cases are
negotiorum gestio (conducting of another person's affairs without their authorization),
unjust enrichment, and
solutio indebiti. This Roman classification is quite controversial for today's standards, since many of these cases would be considered as completely different from contracts (most notably unjust enrichment), and would instead be classified as delicts or special sources of obligations. They are formed by implication from circumstances regardless of the assent or dissent of parties. They are called quasi-contracts. The following are the examples of quasi-contractual obligations under the Roman law;
Quasi-delicts The designation comprised a group of actions that are very similar to delicts, but lacking one of key elements of delicts. It includes
res suspensae, responsibility for things poured or thrown out of buildings, responsibility of shippers/innkeepers/stablekeepers, and erring judges. For example, the responsibility of
innkeepers creates obligations when certain things left by guests in the lodging are destroyed, damaged or lost by the innkeeper's assistants or
employees. In this case, the innkeeper is responsible for the damages to the guest's property, even though he did not cause them personally.
Subject matter Obligations are classified according to the nature of the performance (prestation): • real obligation – related somehow to immovable property • obligation to give – obligations to give or possession, or enjoyment • specific obligation – delivery of a determinate thing when it is particularly designated or physically separated from all others of the same class • generic obligation – delivery of a generic thing • personal obligations – undertakings either to do or not do all kinds of work or service • positive personal obligation – undertaking or obligation to do • negative personal obligation – forbearance or obligation to not do ==Monetary obligations==