Short answer. Three groups: unemancipated minors, insane or demented persons, and — in the Civil Code's own dated wording — deaf-mutes who do not know how to write. What unites them is that the law doubts their ability to understand and weigh what they are agreeing to.
What the law says
The following cannot give consent to a contract: (1) Unemancipated minors; (2) Insane or demented persons, and deaf-mutes who do not know how to write.
Civil Code, Article 1327 — Who Cannot Give Consent. Read the full provision →
Minors — and the age that actually applies
Article 1327 of the Civil Code speaks of unemancipated minors. When the Code was written the age of majority was twenty-one; it is now eighteen, following the amendment introduced by Republic Act No. 6809. So a person of eighteen contracts freely, and it is those below eighteen whom this provision covers.
The incapacity is not absolute in practice. A minor who is emancipated is out of the article altogether. The law also holds minors bound for the reasonable value of necessaries actually delivered to them, and a minor who actively misrepresented his age may be barred from later escaping the contract on the strength of his own deceit.
Insanity, dementia, and the moment that counts
The test is the state of the person at the time of contracting, not before or after. Someone with a diagnosed condition who signs during a genuine lucid interval can give valid consent. Conversely, a person with no diagnosis at all who was incapable of understanding at that moment — through advanced illness, severe intoxication or a hypnotic state — may equally lack capacity.
The second category in the article, deaf-mutes who do not know how to write, is drafted in language that is both dated and narrow. It was aimed at a person who in the 1940s had no available way to receive and express terms. It has no application to a deaf person who reads, writes or signs, and modern practice reads it that narrowly.
The contract is voidable, not void
This is the part that surprises people. Where only one party is incapacitated, the contract is voidable — valid and binding until annulled. It produces effects, and it can be ratified once the incapacity ends, expressly or simply by acting on it. The action to annul runs from the time the guardianship ends or the incapacitated person regains capacity, and it does not last forever.
The rule is different when both parties are incapable of giving consent: the contract is then unenforceable, and no action can be brought on it unless it is ratified.
What to do on either side of the deal
If you are dealing with a minor, contract with the parent or the judicially appointed guardian instead, and remember that a guardian selling or encumbering a ward's property normally needs court approval — a deed signed without it invites a challenge years later.
If an elderly relative has signed a deed while seriously ill, the evidence that decides the case is medical: hospital records, physicians' notes, the notary's own account, and witnesses who saw the signing. Gather it before memories fade. Annulment carries a duty to return what was received, so the practical stakes are not only about undoing the paper. Nobody can promise how a court will assess capacity — bring the documents and the medical records to a lawyer early.
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.
- Samahan ng Magsasaka sa San Josep, et al. vs. Marietta Valisno, et al, G.R. No. 158314, June 3, 2004 — read the decision on LawPhil →