Taxation & Estate Planning
Challenging a will based on mental capacity
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Capacity can be an emotionally charged topic, especially in relation to dementia or Alzheimer's disease and other degenerative conditions. This paper discusses how a Will might be challenged on the basis of mental capacity and why this is such an important issue.

What does capacity mean from a legal perspective?

There are different types and tests of capacity, including the capacity to:

  • make a Will
  • make power of attorney
  • enter into legal proceedings
  • enter into a marriage.
When discussing Wills, we are referring to 'testamentary capacity'. There is an old English case, Banks v Goodfellow, from 1870 which is still good law today. This case sets out what the test for testamentary capacity is. When making a Will, a person must:
  1. understand the nature and effect of a Will—a person must understand the legal document they are preparing, and that it forms their wishes after they pass away.
  2. understand the nature and extent of their property—a person must have a good idea as to what they own, whether that be property, shares, or bank accounts (e.g. those who own a bank account must know which financial institution they bank with, and the approximate account value).
  3. comprehend and appreciate the claims to which they ought to give effect—a person must be able to understand they have a moral obligation to provide for, and the effect of the gifts they are giving, in their Will. They must be able to appreciate that they have a moral obligation to provide for a dependent person, whether that be a spouse or a child, and they must understand how much they ought to provide them and whether that provision is considered 'adequate' for their proper maintenance, support and advancement in life.
  4. not be suffering from any disorder of the mind or insane delusion that would result in an unwanted disposition—this is old terminology, but a person must not be suffering from any condition that affects their mind and capacity to make decisions while taking into consideration the above factors. This arm of the test refers to conditions such as dementia, Alzheimer's disease, etc.
Sometimes it is a difficult exercise to determine whether someone has the requisite testamentary capacity to provide instructions for a Will when they are suffering from dementia or some other injury-caused condition or illness (for instance, a head injury or stroke). In the 19th century English House of Lords case of Boyse v Rossborough (1857) 6 HL Cas 1 at 45, Lord Cranworth, who was also the Lord Chancellor, observed the difficulty in relation to this test:

"There is no possibility of mistaking midnight for noon; but at what precise moment twilight becomes darkness is hard to determine."

This case and comment were referred to and accepted by the same Court in Banks v Goodfellow, some 13 years later and continue to be applied to this day by our state Supreme Courts and the High Court of Australia.

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