A party also may seek to attack the validity of a Will by asserting that the decedent had a diminished mental capacity at the time the Will was executed. In general, a legal presumption applies that the decedent was of sound mind and was competent at the time he/she executed a Will. In fact, the law only requires a minimal degree of mental capacity when executing a Will. Generally, the inquiry is whether the decedent comprehended the property of which he/she wanted to dispose, the beneficiary of said property, and the act of executing the Will. Moreover, this understanding must only be present at the time the Will was executed. Even if the provisions of a Will may be shockingly unnatural or unfair, if it appears that the Will was executed at the time the decedent was competent and that it was the free and unconstrained product of their mind, then the Court should uphold the Will.
Should a beneficiary wish to challenge the validity of a Will based upon the mental capacity of the decedent, the beneficiary would bear the burden of proof to overcome the presumption that the Will was valid. As such, a beneficiary who seeks to uphold the terms of the Will need not establish its validity, but instead, a party who wishes to invalidate a Will must establish the incapacity of the Testator at the time the Will was executed. A challenge to the capacity of a descendent may involve a review of the relevant medical records, testimony of first-hand witnesses, as well as other factors which relate to the competency of the Testator at the time the Will was executed.
This is a general overview as to the mental capacity required of a descendent to execute a Will, as well as what an attack levied by another party seeking to invalidate a Will on the grounds of lack of capacity may entail.