In the Philippines, the legal framework governing surnames is strictly dictated by the Family Code and relevant jurisprudence. When a child is born to a woman who is validly married, the law applies a powerful "presumption of legitimacy." Changing the child's surname to that of the biological father—who is not the legal husband—is not a simple administrative correction; it is a complex legal process that often requires impugning the legitimacy of the child first.
1. The Presumption of Legitimacy
Under Article 164 of the Family Code, children conceived or born during the marriage of the parents are presumed legitimate. This holds even if the mother has declared that the child is not her husband’s, or even if she was committing adultery at the time.
- The Legal Consequence: By law, a legitimate child must use the surname of the father (the legal husband) as per Article 174.
- The "Iron Curtain" Rule: The law protects the status of the child to ensure stability. Only the husband (or in rare cases, his heirs) can contest the legitimacy of the child. The mother or the biological father generally do not have the legal standing to "illegitimize" the child just to change the surname.
2. Can the Mother or Biological Father Initiate the Change?
Generally, no. The Philippine Supreme Court has consistently ruled that the mother cannot unilaterally declare her child illegitimate to accommodate the biological father’s name.
If the child was born while the mother was still legally married to another man (even if they were long separated), the child is legally the husband's. To change the surname, one must first successfully file an Action to Impugn the Legitimacy of the Child.
Grounds for Impugning (Article 166):
- Physical impossibility of sexual intercourse between the husband and wife within the first 120 days of the 300 days preceding the birth (due to distance, imprisonment, or impotence).
- Proof that for biological reasons, the child could not have been that of the husband (DNA evidence is highly persuasive here but must be presented within the context of a court case).
3. The Role of DNA Testing
While DNA testing is the gold standard for proving biological parentage, it does not automatically override the legal presumption of legitimacy. Even if a DNA test proves "Person B" is the father, the child remains "Person A's" (the husband's) legitimate child in the eyes of the law until a court issues a decree of illegitimacy.
4. Scenarios Where Change is Possible
A. The Marriage was Void from the Beginning
If the marriage between the mother and the legal husband is declared void ab initio (e.g., bigamous or lack of license) under Article 35 or 36, the child may be considered illegitimate (unless the marriage was void under Article 36 or 52, where they remain legitimate). If the child is illegitimate, they may use the biological father's surname under R.A. 9255.
B. The Child is Truly Illegitimate
If the mother was not married to anyone at the time of conception and birth, the child is illegitimate. Under Republic Act No. 9255, the child may use the biological father’s surname if:
- The father recognizes the child through the Affidavit of Admission of Paternity.
- The father executes a Private Handwritten Instrument.
5. Proper Legal Remedy: Petition for Correction or Cancellation of Entry
If there is a basis to change the name (e.g., the child was erroneously registered as legitimate when they were actually born out of wedlock), the remedy is a Petition for Cancellation or Correction of Entries in the Civil Registry under Rule 108 of the Rules of Court.
- Nature of Proceeding: This is an adversarial judicial process.
- Parties Involved: The Civil Registrar, the legal husband, and the biological father must all be notified and impleaded.
- Proof Required: Substantial evidence (DNA, birth records, testimonies) to prove that the entry in the birth certificate is a "substantial error."
6. Summary Table: Requirements and Limitations
| Factor | Legitimate Child (Born during marriage) | Illegitimate Child (Born out of wedlock) |
|---|---|---|
| Mandatory Surname | Husband's Surname | Mother's Surname (Default) |
| Can use Bio Father's Name? | No, unless legitimacy is impugned. | Yes, via R.A. 9255 recognition. |
| Who can contest? | Only the Husband/Heirs. | Mother or Father. |
| Primary Law | Family Code, Art. 164-171. | R.A. 9255; Family Code, Art. 176. |
Important Note on "Affidavit of Acknowledgment"
A biological father signing the back of a birth certificate (Affidavit of Admission of Paternity) for a child born during the mother’s marriage to another man is often considered legally void. Because the law already "assigns" a father (the husband), the biological father's acknowledgment cannot coexist with the legal presumption of legitimacy. One must "clear" the husband's name from the document through a court order before the biological father's name can be legally inserted.