20/08/2025
Challenging the validity of a Will: Testamentary Capacity
If you’ve been left out of a Will, or if a Will doesn’t make adequate provision for you, then one line of enquiry you could consider is whether the Will is valid.
Let’s consider a ‘formal’ Will – a written testamentary document signed by the testator (the person who is making their Will) and witnessed by 2 people. For that document to be valid the testator must have had what is known as ‘testamentary capacity’.
Testamentary capacity is a legal test. It is not the same thing as legal capacity in other contexts e.g. whether a person could drive a car, pay their bills or live by themselves without assistance, is not particularly relevant in determining whether a person had testamentary capacity.
The legal test for testamentary capacity requires 3 positive elements. The testator must -
1. Understand the nature of the testamentary act (have the capacity to understand the act of making a Will), and
2. Understand the extent of the property of which they are disposing (they need to understand the extent of what they own and are leaving in their Will), and
3. Have the capacity to understand moral claims of potential beneficiaries.
The legal test for testamentary capacity also has a fourth, negative element. A testator must not be suffering from any ‘insane delusions’ that influence their dispositions under a Will. This might sound odd, however, in a Western Australian case a deceased person was found not to have testamentary capacity because of this fourth element. In that case, a man wrote a close relative out of his Will because he was convinced that she was trying to kill him (she was not!), that she was practising witchcraft (she was not!) and that she had flown into his second storey window to steal his possessions (needless to say, she had not!). This relative challenged the validity of the Will in the Supreme Court. The court found the deceased man did not have testamentary capacity when he re-wrote and executed his Will and therefore it was not a valid Will.
When it is a ‘formal’ Will, the law presumes that the testator had testamentary capacity when they made it. However, there may be facts (supported with evidence) that raise some doubt about testamentary capacity (for example, in a situation where the testator was very old, almost entirely blind, had significant hearing impediment and a cognitive impairment and was very ill). Where a suspicion, based on evidence, is raised that the testator did not have testamentary capacity by facts such as these, then the person propounding the Will bears the onus of proving (with evidence) that the testator did have testamentary capacity.
Importantly, a testator must have had testamentary capacity at the time of making the Will (so for a formal Will, they must have had testamentary capacity when they executed the Will). That’s quite a small window in which a person needs to have testamentary capacity. It means that a person may have several issues impacting on their faculties, like the example above where a woman was 91 years old, was almost entirely blind, had significant hearing impediment and a cognitive impairment, and was very ill, but was still found to have testamentary capacity at the time of executing her Will.
In short, if you want to challenge the validity of a formal Will on the basis of lack of testamentary capacity, you will need persuasive evidence that raises doubt as to the testamentary capacity at the time the deceased person executed their Will. It will then be up to the person propounding the Will to prove the testator DID have testamentary capacity.
This note contains general information only. For legal advice considering your particular circumstances, you will need to obtain legal advice.
Next in this Series on Challenging Testamentary Capacity coming soon: ‘Challenging the validity of a Will – Knowledge and Approval of the Contents’.
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