Short answer. Article 38 of the Family Code voids marriages between collateral blood relatives up to and including the fourth civil degree. This covers first cousins and closer — siblings (second degree), uncle/aunt and niece/nephew (third degree), and first cousins (fourth degree) — whether legitimate or illegitimate.
What the law says
Between collateral blood relatives whether legitimate or illegitimate, up to the fourth civil degree
Family Code, Article 38 — Marriages Void for Public Policy. Read the full provision →
The rule on collateral relatives
Article 38(1) of the Family Code bars marriage between collateral blood relatives, whether legitimate or illegitimate, up to the fourth civil degree. Collateral relatives share a common ancestor but are not in a direct line — brothers and sisters, cousins, uncles and aunts. The prohibition reaches through the fourth degree, making such marriages void from the beginning for reasons of public policy. The illegitimacy of the relationship does not lift the bar: half-siblings and half-first-cousins are treated the same as their legitimate counterparts.
How civil degrees are counted for collateral relatives
Civil degrees for collateral relatives are counted by going up to the common ancestor and then back down to the other party. Brothers and sisters share parents — one step up to each parent makes two degrees. An uncle or aunt and a niece or nephew are three degrees apart: one step up to the sibling, one up to the common grandparent, then one down to the niece or nephew. First cousins are four degrees apart: two steps up to the shared grandparent and two steps back down. All three of these relationships fall within the prohibition.
Who is covered beyond the blood-relative bar
Article 38 lists eight additional categories of public-policy void marriages beyond the blood-relative restriction. These include step-parents and step-children, parents-in-law and children-in-law, an adopting parent and the adopted child, the surviving spouse of the adopter and the adopted child, the surviving spouse of the adopted child and the adopter, adopted children of the same adopter, and — most distinctly — parties where one killed the other's spouse or their own spouse with the intent to marry the other. These are not degrees of blood relation; they are social and familial relationships the law treats as equally incompatible with marriage.
Consequences of a void marriage on public-policy grounds
A marriage void under Article 38 produces no legal bond between the parties. Either party, or an interested third person, may seek a declaration of absolute nullity before the courts. Unlike a voidable marriage, there is no prescriptive period and no ratification — the marriage cannot be cured by cohabitation, consent, or the passage of time. Property, inheritance, and the status of children born of the union are governed by the provisions on void marriages under the Family Code and, where applicable, the Civil Code.
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.
- Republic of the Philippines vs. Marelyn Tanedo Manalo, G.R. No. 221029, April 24, 2018 — read the decision on LawPhil →
- Abigael An Espina-dan vs. Marco Dan, G.R. No. 209031, April 16, 2018 — read the decision on LawPhil →