Matthew T. McDavitt—Senior Attorney
Under U.S. law, a testator drafting a Last Will and Testament must possess testamentary capacity for the document to be legally valid. Testamentary capacity generally requires that the testator understands the nature of their act, knows the extent of their property, and recognizes the natural objects of their bounty (typically family members or loved ones). However, even when these basic requirements are met, a will may still be invalidated if the testator suffered from an "insane delusion" that materially affected the disposition of their estate.
The Legal Framework of Insane Delusion
The concept of insane delusion emerges from the broader requirement of mental soundness in estates law. As articulated in one seminal case, an insane delusion is not merely an eccentric belief or prejudice but "a persistent belief in that which has no existence in fact, and which is adhered to against all evidence.” Colo. Nat'l Bank v. Cole, 75 Colo. 264, 269, 226 P. 143, 145 (1924). For such a delusion to invalidate a will, it must actually influence the testator’s testamentary dispositions—meaning the delusion must be a "causative factor" in how the estate is distributed. "The delusion may have no basis whatever and no evidence may suffice to dispel it, but, if it did not [in fact] influence the testator with respect to the terms of his will, its existence does not invalidate the will." In re Estate of Gammon, No. C7-89-556, 1989 Minn. App. LEXIS 1002, at *4 (Sept. 11, 1989) (quoting In re Estate of Olson, 148 Minn. 122, 124, 180 N.W. 1009, 1010 (1921)). This actual “influence” factor distinguishes insane delusions from harmless quirks or irrational opinions that do not otherwise affect the testator’s testamentary gifts.
Courts typically require evidence that the delusion lacks any rational basis and that it materially altered the testator’s intent. “The contestant bears the burden of proving that the testator suffered from an insane delusion, that he was under such a delusion at the time of making his will, that the insane delusion materially affected the disposition made in the will, and that the will was the product of the insane delusion.” Romero v. Vasquez (In re Estate of Romero), 126 P.3d 228, 232 (Colo. App. 2005).
Examples of Insane Delusions
One recurring example involves a testator’s unfounded belief that their spouse was unfaithful or that their children were illegitimate. In In re Honigman's Will, 8 N.Y.2d 244, 248, 203 N.Y.S.2d 859, 168 N.E.2d 676 (1960), a New York court invalidated a will where the testator disinherited his wife based on his unfounded suspicion of her infidelity. Despite no evidence supporting this belief—and substantial evidence to the contrary, including a long, stable marriage—the testator clung to the delusion, writing his wife out of the will entirely. The court found that this fixed false belief materially affected the disposition, rendering the will invalid. The decision emphasized that the delusion must be more than mere suspicion; it must be a belief so irrational and persistent that it overrides reality.
Conversely, note that solely testamentary gifts made or denied based on a testator’s delusions potentially support a finding of insane delusion; a testator’s mere conspiratorial beliefs not impacting any testamentary gift will not support invalidation of a will. See Breeden v. Stone (In re Estate of Breeden), 992 P.2d 1167, 1169 (Colo. 2000) (because a decedent's insane, but immaterial, delusions regarding his friends and government agencies did not affect or influence the disposition of his property by will, such that delusions did not vitiate the will).
Accordingly, the party contesting the will must show that but for the delusion, the will would be materially different. Thus, the test is whether the testator suffered from an insane delusion that gave rise to the will, or materially affected the will, by rendering the testator incapable of understanding the extent of his or her property, the natural or proper objects of his or her bounty, or the nature of his or her testamentary act.
In re Estate of Kottke v. Parker, 6 P.3d 243, 246 (Alaska 2000).
Conclusion
Under U.S. law, an insane delusion sufficient to invalidate a Last Will and Testament must be more than a mistaken belief or prejudice—it must be a persistent, irrational conviction that lacks any evidentiary basis, and materially affects the will’s provisions. While the subjects of insane delusions are multifarious, such unsupported belief must demonstrably drive the testamentary disposition. These examples underscore the delicate balance courts strike between honoring a testator’s autonomy and ensuring their decisions reflect a sound mind, offering a robust framework for challenging wills tainted by mental incapacity.
