Extrinsic evidence is external, outside evidence or evidence that is inadmissable or not properly before the court, jury, or other determining body. Extrinsic evidence is often referred to in the context of interpretating a will that is vague. Arguments to bring in extrinsic evidence in such a situation include:
1. There is a latent ambiguity. Ambiguity does not appear on face of will but appears when terms of will are applied to the testator's property or designated beneficiaries. Admission of evidence to clarify latent ambiguity first began in cases of equivocation--where description fits 2 or more external objects equally well (i.e., devise to my niece Alicia, when testator has 2 nieces named Alicia.)
2. Scrivener's error. The person writing the will made a mistake in transcribing the will.
3. Personal usage exception to plain meaning: If extrinsic evidence shows that the testator always referred to person in idiosyncratic manner, evidence is admissible to show that the testator meant someone other than person with legal name of legatee.
4. Patent ambiguity--ambiguous on its face. In some states, evidence is NOT admissible to clarify ambiguity, & wills fails, but courts have often disposed of problems by simply construing language of will without aid of extrinsic evidence.
Whether an ambiguity is patent or latent may depend upon who the reader is.