Does dementia make a will invalid?
Suppose you felt that you’d been unfairly cut out of your mother’s will. Doctors diagnosed her with dementia and she became convinced that you were possessed by demons and rode around on a broomstick.
You would have thought you’d have a good case that your mother lacked the necessary testamentary capacity to write a will. But it isn’t necessarily so.
Why? Because testamentary capacity is determined by law, rather than being based on a medical diagnosis.
Legal and mental ability required to write a will
At the time of writing a will, a testator – the person writing the will – must have the mental capacity to understand the nature of making the will and the effect it will have.
They need to understand the extent of the assets being distributed in the will and comprehend the moral claims of potential beneficiaries.
The testator can’t be suffering from any condition, such as dementia, that interferes with their normal decision making.
How is testamentary capacity defined in law?
The legal foundation for testamentary capacity rests on a British judicial decision made 150 years ago in Banks v Goodfellow (1870) LR 5 QB 549.
In the decision the judge said:
It is essential to the exercise of such a power that a testator shall understand the nature of the act and its effects; shall understand the extent of the property of which he is disposing; shall be able to comprehend and appreciate the claims to which he ought to give effect; and that no disorder of the mind shall poison his affections, pervert his sense of right, or prevent the exercise of his natural faculties—that no insane delusion shall influence his will in disposing of his property and bring about a disposal of it which, if the mind had been sound, would not have been made.
In 1941 the Australian High Court confirmed this legal basis.
Testamentary capacity increasingly in dispute
With an ageing population and an increasing trend to challenge wills, due to the high value of homes and property, there is a growing focus on whether a testator has testamentary capacity.
This is particularly the case when a person changes their will while being cared for by an individual who suddenly emerges as the chief beneficiary.
Dementia diagnosis does not automatically remove testamentary capacity
In a recent case, two sisters fought to have their father’s will overturned, claiming he suffered from dementia and hallucinations that took away his mental capacity to make a will. (See Croft v Sanders  NSWCA 303.)
The father’s first will distributed his assets evenly among his six daughters. But late in life, he changed his will to leave five of the daughters $40,000 each, while one daughter got $3 million.
There were divisions in the family, and the father decided to give the bulk of his estate to the daughter who stuck by him and helped run his business.
The two sisters argued their father had dementia and lacked capacity when he made the second will. He believed that they ran a brothel, were demons and had kidnapped their mother, and that a panther lived in the garden.
The NSW Court of Appeal upheld an earlier court decision. The court stated that the father’s doctors, along with evidence produced by the daughter who got the bulk of the estate, suggested that dementia had not deprived him of testamentary capacity.
The judge concluded that the father’s delusional beliefs were episodic, that he had the ability to rationalise, as he had made rational business decisions at the time, and therefore he met the criteria for being able to make a will.
No one-size-fits-all answer to question of testamentary capacity
This judgement demonstrates that under the law, a diagnosis of dementia doesn’t necessarily mean that a person lacks the capacity to make a will.
Every challenge to a will has unique factors, and a judge will weigh all of these, especially the intent of the testator.
If you would like to learn more about the law in relation to testamentary capacity, please refer to my basic guide and our earlier articles.