Short answer. A direct line runs straight up or down your own family tree — your parents, grandparents, children, and grandchildren. A collateral line runs sideways: relatives who share a common ancestor with you but are not your own ascendants or descendants, such as siblings, aunts, uncles, and cousins. Succession law treats the two lines differently.
What the law says
A direct line is that constituted by the series of degrees among ascendants and descendants. A collateral line is that constituted by the series of degrees among persons who are not ascendants and descendants, but who come from a common ancestor.
Civil Code, Article 964 — Lines of Relationship. Read the full provision →
What a 'line' means here
Article 964 explains relationship in terms of a series of degrees, and calls that series a line. Each generation separating two relatives counts as one degree, and the path traced through those degrees, from one relative to another, is the line. The article recognizes only two kinds: a line is either direct or collateral, depending on whether the people at each end of it descend from one another or merely share an ancestor further back.
The direct line: ascendants and descendants
A direct line is the series of degrees among ascendants and descendants — people who descend one from the other. Your parent, grandparent, and great-grandparent sit on the ascending direct line; your child and grandchild sit on the descending direct line. What makes a relationship direct is that one person is literally a forebear or offspring of the other, with no branching involved. This is the line succession law leans on most heavily, since it is where the closest compulsory heirs — children and, failing them, parents — are found.
The collateral line: a shared ancestor, not a shared descent
A collateral line covers everyone else who is still related by blood: people who are not ascendants or descendants of one another, but who trace back to a common ancestor. A sibling is the closest example — you and your sibling do not descend from each other, but you share a parent. The same logic reaches further out to aunts, uncles, nieces, nephews, and cousins, all of whom connect to you only by going up to a shared ancestor and back down a different branch.
Why the distinction is not just terminology
Succession law does not treat every blood relative the same way, and which line a person sits on is often the first question. Direct-line descendants and ascendants are given priority and, for children in particular, a legitime the estate cannot bypass. Collateral relatives generally come into the picture only in intestate succession, and only once closer heirs in the direct line are absent, since the law's default preference runs straight up and down the family tree before it turns sideways to siblings, cousins, and other collateral relatives.
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.
- Maria Mendoza, et al. vs. Julia Policarpio, et al, G.R. No. 176422, March 20, 2013 — read the decision on LawPhil →