A contractual obligation must be possible, permissible, and determined or determinable.121 This is a condition for the valid conclusion of a contract. If the subject of the obligation is impossible, impermissible, undetermined, or indeterminable, the contract is null and void.122
The subject of an obligation is impermissible if it contradicts the constitution, mandatory regulations, or moral principles.123
Example: A and B agree that A will give false testimony in court, and B will pay him for it.
The subject of an obligation is determinable if the contract contains data that allow it to be determined or if the parties have assigned a third party to determine it. If this third party refuses or is unable to determine the subject of the obligation, the contract is null and void.124 Determinability of the subject means that it is known and specified at the time of contract formation.
The subject of an obligation must also be possible, meaning that both legal and factual fulfilment of the obligation must be feasible.
Example of factual impossibility: The subject does not exist.
Example of legal impossibility: A regulation does not permit fulfilment.
In addition to these characteristics of the subject, a valid contract must also have a permissible contractual basis (reason). A contractual basis is impermissible if it contradicts the constitution, mandatory regulations, or moral principles. It is presumed that an obligation has a basis, even if it is not explicitly stated. If there is no basis or if it is impermissible, the contract is null and void.125
