Definition
A French legal term meaning "under private signature." A sous seing privé is a written contract or legal instrument executed and signed privately by the parties themselves, without the involvement of a notary, judge, or other public officer. The term is used primarily in Louisiana law, which inherited it from the French civil law tradition.
A sous seing privé stands in direct contrast to an authentic act—a document formally executed before a notary or other public officer whose intervention lends the document heightened evidentiary weight and legal presumptions. The privately signed instrument carries legal force but lacks the procedural formalities and attendant presumptions that accompany the authentic act.
Common Confusion
SOUS SEING PRIVÉ vs. AUTHENTIC ACT: These two categories together exhaust the formal taxonomy of written instruments in Louisiana's civil law tradition. Researchers should not treat sous seing privé as a defective or lesser document in an absolute sense—it is a fully valid legal instrument. The distinction is evidentiary and procedural: authentic acts carry a presumption of authenticity and are harder to challenge, while a sous seing privé may be contested more readily, including by denial of signature. Confusing the two leads to misreading Louisiana cases that turn on which type of instrument was at issue, particularly in disputes over proof of execution.
Why It Matters in Research
This term is almost exclusively a Louisiana research issue. Because Louisiana's private law descends from French and Spanish civil law rather than English common law, its vocabulary of written instruments does not map onto categories familiar from other American jurisdictions. A researcher working in Louisiana contract law, property records, successions, or notarial archives will encounter this phrase routinely in historical documents, pleadings, and judicial opinions.
The central research trap is applying common law evidentiary assumptions to instruments labeled sous seing privé. In common law jurisdictions, private written contracts carry no formal categorical distinction from notarized ones beyond the notary's role as a witness to signature. In Louisiana civil law, the sous seing privé / authentic act distinction is a structural feature of the law itself, affecting how instruments are proved, challenged, and recorded.
Researchers in Louisiana property records should note that instruments affecting immovable property (real estate) were often required to be in authentic form—meaning that a sous seing privé found in a chain of title may raise questions about the instrument's effectiveness against third parties, a distinction that generated substantial Louisiana jurisprudence in the nineteenth and early twentieth centuries. When reading older Louisiana cases, verify which article of the Civil Code of Louisiana was in effect; the relevant provision has been renumbered across successive codifications.
Outside Louisiana, the term appears in American legal literature almost exclusively in comparative law contexts, in treatises discussing civil law systems, or in cases involving contracts formed in France or other civil law jurisdictions where Louisiana courts or federal courts were asked to interpret foreign instruments.
Historical Dictionary Support
The four source dictionaries are in close agreement, which reflects the term's narrow and well-defined function in the civil law tradition. Black's (both editions) and Bouvier's share nearly identical language defining the term as "under private signature" and situating it against the authentic act. Anderson adds the useful characterization of the underlying document as a "private act," a phrase that surfaces in Louisiana judicial opinions and helps researchers identify synonymous terminology in case law.
All four sources anchor the term to Louisiana law and reference the contrast with the authentic act as the essential definitional content. None of the dictionaries address the evidentiary consequences of the distinction in any depth, nor do they flag the title-chain and third-party effects that make the distinction practically significant in property research. Researchers should not rely on these entries alone when the sous seing privé / authentic act distinction is outcome-determinative; the Louisiana Civil Code and Louisiana treatises on notarial law provide the operative framework.
Jurisdictional Note
Sous seing privé is a term of Louisiana civil law and has no operative legal meaning outside that jurisdiction in American practice. Researchers encountering the term in federal cases should determine whether the court is applying Louisiana law or interpreting a foreign civil law instrument; the analysis differs substantially between those contexts.