Here’s a comprehensive, practice-oriented legal explainer—Philippine context—on Inheritance Rights When Heirs Are Deceased. It ties together intestate and testamentary succession rules, representation, accretion, substitution, hereditary transmission, legitimes, and tricky edge cases (e.g., simultaneous death, preterition, disinheritance, renunciation, illegitimacy, half-blood, adoption, reserva troncal). No web sources used.

1) First principles: when and how succession opens

Succession opens at the moment of the decedent’s death. From that instant, the decedent’s property, rights, and obligations transmissible by law pass to his/her heirs (Art. 777 Civil Code concept).
A person can inherit only if alive (or conceived) at the time succession opens. A conceived child (nasciturus) inherits if later viably born.
If the “heir” predeceased the decedent, he/she obviously cannot inherit; the law then asks: does someone step into that slot (representation)? Or does the share merge with others (accretion/intestacy)? Or did the will name a substitute?

2) Compulsory heirs, legitime, and the free portion

Compulsory heirs: (a) legitimate children/descendants; (b) surviving spouse; (c) legitimate parents/ascendants (only if there are no descendants); (d) illegitimate children (with distinct rules); plus certain special regimes (e.g., adopted children, treated as legitimate).
The estate splits into the legitime (reserved by law for compulsory heirs) and the free portion (testator may dispose of by will, subject to reductions if too generous).
If a compulsory heir predeceases, his/her descendants may represent (Section 4 below). The surviving spouse never represents anyone; he/she takes in his/her own right.

3) Four different ideas people mix up

Representation (legal stepping-into the shoes of a predeceased/disinherited/incapacitated heir).
Accretion (a co-heir’s share merges into the shares of the other co-heirs when the co-heir cannot take and nobody may represent).
Substitution (the will names a backup heir to take if the instituted heir cannot/does not).
Hereditary transmission (the right to inherit that has already sprung in favor of an heir who then dies after the decedent, passes to that heir’s own heirs, even if he never got to accept the inheritance formally).

Keep them separate; they lead to very different outcomes.

4) Representation (who may “step into the shoes”)

4.1 Direct descending line (children → grandchildren → great-grandchildren)

Always allowed by law. Descendants represent their ascendant (the predeceased child) and collectively take the share that would have gone to that ascendant (they divide per stirpes, i.e., by branch).
Representation also works if the parent is disinherited or incapacitated (e.g., unworthy), but not if the parent renounced the inheritance (see 4.4).

4.2 Collateral line (brothers/sisters → nephews/nieces)

Allowed only for the children of brothers and sisters of the decedent. Thus, nephews/nieces may represent a predeceased/disinherited/incapacitated sibling of the decedent. It does not extend to grandchildren of siblings (no representation of great-nephews/nieces).

4.3 Ascending line (parents, grandparents)

No representation upward. If a parent predeceases, the other parent/ascendants take by their own right; nobody “represents” the predeceased parent upward.

4.4 Effect of renunciation

He who repudiates (renounces) the inheritance cannot be represented. If a child renounces, his descendants do not step into his place; the share is redistributed via accretion or intestacy.

4.5 The “iron curtain” (illegitimate vs. legitimate families)

The law bars succession between an illegitimate person and the legitimate relatives of his/her father or mother (the classic Art. 992 rule). Practical effects:
- An illegitimate grandchild cannot represent his illegitimate parent to inherit from the legitimate grandparent (and vice versa).
- But an illegitimate child may represent for his illegitimate parent in the direct line within the same side (observe the barrier when it crosses to legitimate relatives).
- These barriers do not apply within fully legitimate lines, and adopted children are treated as legitimate with their adoptive family.

5) Accretion (when shares “merge”)

Testamentary accretion: If a will gives a portion to several heirs jointly and one cannot take (predeceased, incapacity, renunciation), and there is no representation and no substitution, the others in that group take the vacated share pro rata (subject to legitimes and reductions).
Intestate accretion: If there’s no will or the will doesn’t cover the entire estate, intestacy rules reallocate the free share to the proper class (e.g., other children, spouse, ascendants).

6) Substitution (only if the will says so)

Vulgar substitution clause (“If A cannot inherit, B shall take”) defeats accretion and sidelines representation except where representation is mandatory to protect legitimes (e.g., compulsory heirs in the direct line).
Pupillary/fideicommissary substitutions have special formalities and limits; these are rarer in practice.

7) Hereditary transmission (heir dies after the decedent)

If an heir survives the decedent (even by a moment), the right to the inheritance vests in that heir from the time of the decedent’s death.
If that heir dies later (before accepting, before partition, or during settlement), his/her own heirs inherit his share or his right to accept—this is hereditary transmission, not representation.
Thus, do not ask “who represents him?”—you settle his estate, which now includes the (unaccepted) inheritance or the right to accept/repudiate it.

8) Simultaneous death (commorientes)

If it cannot be proved who died first (e.g., common calamity), the law presumes no transmission between them. Each decedent is settled as if the other never inherited.
This matters for spouses or parent-child pairs dying together: it blocks representation via that person and shifts the estate to the next eligible class.

9) Intestate succession when a child is already deceased

Order and shares (simplified, common scenarios):

9.1 Decedent leaves: spouse + children, but one child predeceased leaving descendants

Rule: Living children + grandchildren by representation form one class.
Shares: The branch of the predeceased child takes the same share that child would have taken, divided among the grandchildren per stirpes.
Spouse: shares as a child (in intestacy), i.e., equal to one legit child’s share (subject to the full Civil Code detail on legitimes when there is a will).

Example Estate ₱9,000,000. Heirs: Wife W; Child C1 (alive); Child C2 (predeceased) with two kids GC21, GC22.

Stems: C1 and C2 → 2 stems.
Each stem gets ₱4.5M.
C1 gets ₱4.5M.
C2’s stem: GC21 ₱2.25M; GC22 ₱2.25M. (If intestate with a spouse, adjust per statutory rules: many practitioners treat the spouse like a child in intestacy with descendants; in testamentary legitime computations the spouse’s legitime and children’s legitime are computed under the legitime matrix—see 10.)

9.2 Decedent leaves: parents/ascendants but no descendants

If a parent predeceased, the other parent/ascendants inherit; no representation upward; siblings and their children may come in depending on the presence of the spouse and ascendants under the intestate ladder.

9.3 Decedent leaves siblings, but some siblings predeceased leaving nephews/nieces

Representation allowed only by children of brothers/sisters.
Full-blood vs half-blood: In intestacy among collateral relatives, a half-blood sibling generally takes half the share of a full-blood sibling; when representing, the branch inherits what the represented sibling would have received, applying the full- vs half-blood distinction at that level.

10) Testamentary succession when a compulsory heir is already deceased

Legitime protection: A will cannot impair the legitime of compulsory heirs. If a child predeceased, his descendants represent to claim that child’s legitime.
If the will instituted the predeceased child as heir without a substitute:
- The descendants of that child step in by representation for the legitime and may also take in the free portion if representation is recognized by the will’s terms; otherwise the free portion may accrete or fall to intestacy.
Preterition (omitting a compulsory heir in the direct line): generally annuls the institution of heirs to the extent necessary; if the omitted compulsory heir predeceased leaving descendants, courts protect the branch’s legitime (reduce dispositions).

11) Disinheritance, incapacity, and renunciation

Disinheritance (must be for a legal cause and in a will with due formalities): the disinherited child’s descendants represent him for the legitime; the disinherited parent gets nothing, but the branch remains protected.
Incapacity/Unworthiness (e.g., attempted murder of the decedent): treated like predecease for purposes of representation by descendants.
Renunciation/repudiation: No representation of a renouncer. His share goes by accretion or intestacy.
Partial acceptance is not allowed; acceptance or repudiation is indivisible as to the share (though one may accept inheritance and repudiate a devise/legacy under specific conditions).

12) Adopted children, stepchildren, and illegitimate children

Adopted child = legitimate child of the adopter for succession (full rights in the adoptive family). Ties with the biological family are generally severed for succession (subject to the adoption regime in force at the time).
Stepchildren (no adoption) do not inherit intestate from stepparents; they need a will or donation.
Illegitimate children: compulsory heirs with their own legitime fraction; observe the iron curtain (no succession between an illegitimate person and the legitimate relatives of his/her parent), which also blocks representation across that barrier.

13) Debts, collation, inofficious donations, and partition

Estate pays debts first. Heirs ultimately receive net estate.
Collation: Property donated to descendants during the decedent’s lifetime may have to be brought to collation to compute shares fairly, unless expressly exempt. Predeceased donees’ shares are computed via representation at the branch level.
Reduction of inofficious donations: Lifetime gifts that invade legitimes are reduced.
Partition: Heirs may partition at any time; if a representing branch exists, that branch takes as one stem first, then distributes within.

14) Reserva troncal (special, but often exam-triggered)

If an ascendant inherits from a descendant property that the descendant received by gratuitous title from another ascendant or sibling within the third degree, the property is “reservable”.
When that ascendant (the reservista) later dies, the property must return to the relatives within the line from which it came (reservatarios).
This can override what would otherwise be a normal distribution—important where multiple deaths occur and an intermediate heir has already died.

15) Worked mini-scenarios

15.1 Predeceased child with grandchildren (testate; no substitution stated)

Will leaves everything to A and B (children). B died earlier, leaving three kids.
- Legitime: the branch of B (his three kids) is entitled to B’s legitime by representation.
- Free portion: If the institution to A and B is joint and no substitution is named, the free portion intended for B accretes to A unless the will or law indicates representation also applies there; courts ensure legitime first, then accretion applies to any excess.

15.2 Heir survives decedent then dies before partition

D dies → Son S survives (so S becomes heir at that moment) → a week later S dies, leaving Wife W and Child C.
- S’s share in D’s estate becomes part of S’s own estate by hereditary transmission; W and C inherit from S (not by representing S in D’s estate). Two estates are settled (often consolidated for efficiency).

15.3 Simultaneous death of spouses

Spouses die in the same accident; order of death cannot be proved.
- No transmission between them. Each spouse’s estate is settled as if the other predeceased without issue through him/her; property co-owned is divided per co-ownership/conjugal rules, then each share devolves to that spouse’s heirs.

15.4 Renunciation by a child

Child X renounces. X’s own kids cannot represent X. The vacant share goes to co-heirs by accretion or per intestacy.

15.5 Collateral line representation

Decedent leaves no spouse/descendants/ascendants, only siblings, but Sister S predeceased leaving Son N (nephew).
- N represents S, taking S’s share. If Brother B is half-blood, he gets half of a full-blood share; N gets what S (full or half-blood) would have gotten.

16) Practical road map in real cases

Fix the family tree (who’s alive at death; who is predeceased; who left descendants).
Classify: Are we in the descending line (children/grandchildren), collateral (siblings/nephews/nieces), or ascendants?
Apply representation rules (only where allowed; watch for renunciation and iron curtain).
Check the testament: any substitutions? Is the institution joint (possible accretion) or separate amounts? Any preterition?
Compute legitimes; reduce inofficious dispositions/donations if needed; collate advances.
Separate debts and conjugal/co-owned property before distribution.
For heirs who died after the decedent, apply hereditary transmission (settle their estates too).
Document everything; consider extrajudicial settlement if all heirs are of age, known, and in agreement, otherwise go to estate proceedings.

17) Quick answers to common questions

Do grandchildren automatically get a share if their parent (the decedent’s child) died first? Yes—by representation, they take their parent’s share (per stirpes).
Can I represent a parent who just refused his share? No. Renunciation kills representation.
My illegitimate child—can he represent me to inherit from my legitimate parents? Generally no (the iron curtain blocks succession between illegitimate persons and the legitimate relatives of the parent).
Adopted child vs biological: Adopted child inherits from adoptive parents as a legitimate child.
What if the will forgot a child? Possible preterition—institutions can be annulled/reduced to protect the omitted compulsory heir (or his branch if he predeceased).
What if order of death is unknown? No inheritance between them; each estate is settled separately.

Bottom line

When an heir is already deceased, ask first: representation, accretion, substitution, or hereditary transmission?

Representation protects branches (descendants and, in a narrow slice, nephews/nieces).
Accretion lets co-heirs absorb a vacant share if nobody can represent and there’s no substitute.
Substitution works only if the will says so.
Hereditary transmission handles the case of an heir who survived the decedent but died later—the right passes to his own heirs. Layer on the rules for legitimes, debts, collation, illegitimacy barriers, adoption, and half-blood, and you can reliably map any distribution.

If you want, tell me your family tree with dates of death, whether there is a will, who renounced (if any), and any lifetime donations, and I’ll run an exact per-branch computation and draft a distribution table you can use in an extrajudicial settlement or in court.