On what specific grounds can a husband legally dispute that a child born during the marriage is his?

The word that does most of the work is ‘only’

Article 166 is not a list of examples. It says legitimacy may be impugned only on the grounds that follow, which makes the list closed. A husband who is certain, who has been told so by relatives, or who simply no longer believes the child is his has not thereby stated a ground. He has to bring his situation inside one of three described categories, and if the facts do not fit any of them the action fails regardless of how sincerely held the belief is. That closure is deliberate: the Code treats the legitimacy of a child born in marriage as a status not to be unsettled on suspicion.

The 120-day window, and the three ways of proving impossibility

The first ground is arithmetical before it is evidentiary. Count back 300 days from the birth; the relevant period is the first 120 days of that stretch. Impossibility outside that window is beside the point. Within it, the article names three causes and no others: the husband's physical incapacity for intercourse, the fact that the spouses were living separately in such a way that intercourse was not possible, and serious illness of the husband that absolutely prevented intercourse. Each is demanding on its own terms. Living in different cities is not automatically living separately in such a way; illness has to have absolutely prevented intercourse, not merely made it unlikely.

Science, and the narrow insemination ground

The second ground allows proof that for biological or other scientific reasons the child could not have been the husband's — expressly excepting the artificial insemination situation the Code deals with in Article 164. This is the ground modern testing speaks to, and it is framed as proof of impossibility rather than of probability. The third ground is narrower still and applies only where the child was conceived through artificial insemination: it attacks the written authorisation or ratification itself, on the footing that either parent's consent was obtained through mistake, fraud, violence, intimidation or undue influence. It is a consent defect, not a paternity dispute in the ordinary sense.

Grounds are only half the problem

Article 166 says what may be argued. It does not say who may argue it, or for how long the option stays open — the Code deals with both separately, and the limits there are short and unforgiving. That sequencing matters practically, because a husband who spends a year gathering proof of a good ground can find the route closed for reasons that have nothing to do with the merits. Two other things are worth knowing before anyone acts. A mother's own statement against the child's legitimacy does not establish it, as Article 167 makes plain. And the birth certificate entry is not the status; it is a record of it.

Cases citing this provision

These Supreme Court decisions cite the provision above. We list them so you can read them yourself; the summaries of what each decided are not ours to give.

• Bernie Santiago vs. Rommel C. Jornacion and The City Civil Registrar of Marikina City, G.R. No. 230049, October 6, 2021 — read the decision on LawPhil →
• Lowella Yap vs. Almeda Yap, Hearty Yap-Dybongco and Diosdado Yap, Jr, G.R. No. 222259, October 17, 2022 — read the decision on LawPhil →
• Richelle Busque Ordoña vs. The Local Civil Registrar of Pasig City and Allan D, G.R. No. 215370, November 9, 2021 — read the decision on LawPhil →
• Eugenio San Juan Geronimo vs Karen Santos, G.R. No. 197099, September 28, 2015 — read the decision on LawPhil →

Related provisions

• Family Code, Article 166 — Grounds to Impugn Legitimacy
• Family Code, Article 167 — Mother's Declaration Cannot Bastardize the Child