Short answer. Five grounds: defective execution or attestation, the testator's insanity or mental incapacity when the will was made, execution under duress or fear, procurement through undue pressure by a beneficiary or someone acting for the beneficiary's benefit, and a signature obtained by fraud or trick.

What the law says

The will shall be disallowed in any of the following cases: (a) If not executed and attested as required by law; (b) If the testator was insane, or otherwise mentally incapable to make a will, at the time of its execution; (c) If it was executed under duress, or the influence of fear, or threats; (d) If it was procured by undue and improper pressure and influence, on the part of the beneficiary, or of some other person for his benefit; (e) If the signature of the testator was procured by fraud or trick, and he did not intend that the instrument should be his will at the time of fixing his signature thereto.

Rule 76, Section 9 — Grounds for disallowing will. Read the full provision →

An exclusive list

The rule sets out five specific grounds on which a will must be disallowed, covering defects in how the will was executed and attested, the testator's mental incapacity at the time of execution, execution under duress or fear or threats, procurement through undue pressure by or for a beneficiary, and a signature obtained through fraud or trick where the testator never intended the document to be a will at all.

Defects in execution vs defects in the testator's will

Some grounds are purely formal, like a failure to execute and attest the will the way the law requires, while others go to the substance of the testator's free and informed consent, such as insanity, duress, fear, threats, or undue pressure exerted for a beneficiary's advantage. Either type of defect is enough on its own to disallow the will. A will can be flawlessly executed on paper — properly signed, witnessed, and attested — and still be disallowed if the testator lacked the mental capacity to make it, since formal compliance alone does not cure a defect in the testator's actual capacity or consent.

Pressure, fraud, and trickery

The last two grounds specifically target manipulation of the testator rather than defects in form: undue and improper pressure exercised on the testator by or for the benefit of a beneficiary, and outright fraud or trickery that procures the testator's signature without the testator actually intending the document to function as a will at that moment in time. The fraud ground is narrower than it might first appear — it requires that the testator did not intend the instrument to be his will when signing it, which distinguishes genuine trickery about the document's very nature from a testator who understood exactly what he was signing but was simply misled about some fact affecting its contents.

Related provisions

Note. Statute text quoted on this page is reproduced from the official enactment and is linked to the full provision. The explanation around it is general legal information from Vivas & Nobles Law Office, not legal advice. Whether it applies to your situation depends on facts only a lawyer reviewing them can assess.