Short answer. Under Article 374 of the Civil Code, it is the younger person who is legally required to add an additional name or surname to avoid confusion when two people share identical names and surnames. The older person keeps their name unchanged; the duty to distinguish falls entirely on the one who came second.
What the law says
the younger person shall be obliged to use such additional name or surname as will avoid confusion
Civil Code, Article 374 — Identical Names: Younger Adds. Read the full provision →
The rule: who must add something
Article 374 of the Civil Code is brief but clear: "the younger person shall be obliged to use such additional name or surname as will avoid confusion." Age is the deciding factor. If you share a complete name — first name and surname — with an older person, the law places the obligation on you, not on them. The older person keeps their name exactly as it is; the younger one must add a word or element that sets them apart.
What counts as a sufficient addition
The statute requires only that the addition avoid confusion — it does not specify what form that addition must take. In practice, a middle name, a suffix such as Jr., or a maternal surname can each serve this purpose. The goal is practical: anyone reading a document, receiving a letter, or searching a registry should be able to tell the two individuals apart. An addition that still leaves confusion intact does not satisfy the obligation.
Why this matters in real life
Shared names create friction across almost every official record: land titles, court filings, bank accounts, voter registration, civil registry entries, professional licenses. When two people with identical names each claim a document or right, the younger person's failure to distinguish themselves can result in mistaken entries, delayed transactions, or legal proceedings directed at the wrong individual. The Article 374 rule exists precisely to prevent these mix-ups before they happen, by placing the duty to act on the person who arrived at the name second.
What the rule does not cover
Article 374 addresses the specific case of identical names and surnames — both the given name and the family name must match. A person with a common surname but a different first name is not covered by this obligation. The article also does not define which additional element is acceptable; it says only that whatever is used must avoid confusion. The civil registry, professional licensing bodies, and the courts each apply the rule in their own context, and the manner of distinguishing may differ across those settings.
How to act on this rule
If you are the younger of two people sharing a full name, review your government-issued identification, professional registrations, and any regularly used documents. The practical step is to consistently use the distinguishing element in all formal contexts — not only when confusion actually arises, but as a standing practice. Consistency matters: using an addition in some documents and not in others can itself create a discrepancy that raises new questions. If you are uncertain whether your current documentation satisfies the requirement or creates a record conflict, a lawyer can review the specific situation.