The cause is, for a part of legal doctrine, one of the essential elements of the legal act, together with the will and the object. Traditionally it has been considered that the cause consists in the purpose that each subject pursues when contracting an obligation. It is also important to know the cause of the contract to determine if it is lawful.
The contract that has no cause or whose cause is unlawful will be nonexistent (only in the first case) or null, depending on the doctrinal position adopted. An unlawful cause will be considered when it is prohibited by law, contrary to good customs or public order.
This should not be confused with the case in procedural law, which refers to the litigation that is settled in court. In that sense, "knowing a cause" means being a judge in the litigation.
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