Short answer. The Family Code classifies filiation as natural or by adoption, and natural filiation as legitimate or illegitimate. The dividing line is the parents' marriage: it decides which set of rules governs the child's surname, parental authority, support and inheritance share — not whether the child is a child.
What the law says
The filiation of children may be by nature or by adoption. Natural filiation may be legitimate or illegitimate.
Family Code, Article 163 — Kinds of Filiation. Read the full provision →
Two words that do a lot of quiet work
Article 163 of the Family Code sets the whole framework in two sentences: The filiation of children may be by nature or by adoption. Natural filiation may be legitimate or illegitimate. Filiation is the legal relationship between parent and child. The first sentence says that relationship can arise either from birth or from adoption; the second divides children related by birth into two classes. Nearly every later rule about children in the Code refers back to which class a child falls into, which is why so much turns on this short provision.
What actually differs
Both classes of children are the children of their parents, and both are entitled to support and to be recognised. What the classification changes are specific consequences: which surname the child uses and on what conditions, which parent exercises parental authority in the ordinary case, and the size of the child's legitime when a parent dies. An illegitimate child's inheritance share is fixed by law at a fraction of a legitimate child's, and that difference persists no matter how the family actually lived. The label is a legal category with defined effects, not a comment on the child.
Proof of filiation is a separate question from class
It is worth separating two things that are often confused. Whether a child is legitimate or illegitimate depends on the parents' marriage; whether the child's filiation to a particular parent is established at all depends on evidence — the record of birth, an admission in a public document, a signed private handwritten instrument, or the other means the Code allows. A child may be indisputably illegitimate yet have no established filiation to the father, and establishing that link is usually the first step before any question of support, surname or inheritance can be pursued.
Where the marriage line is actually drawn
The Code fills in Article 163's division concretely elsewhere: a child conceived or born during the parents' marriage is legitimate, while a child conceived and born outside a valid marriage is illegitimate, unless the Code itself provides otherwise. Children conceived through artificial insemination of the wife are also treated as legitimate, but only if both spouses authorized or ratified the procedure in a written instrument signed before the child's birth and recorded with the birth certificate. Edge cases around a mother's remarriage after an earlier marriage ends have their own separate timing rules for which marriage a child is presumed conceived under.
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.
- Alejandra Arado, et al. vs. Anacleto Alcoran and Elenette Sunjaco, G.R. No. 163362, July 8, 2015 — read the decision on LawPhil →