Logically, we therefore need to know what is meant by mental capacity and what standard is required.
Perhaps surprisingly, in the context of making a Will, ‘capacity’ does not mean the definition as set out in the Mental Capacity Act 2005 – confirmed by two recent cases: James v James and others  EWHC 43 (Ch) and Walker (Deceased), Re  EWHC 71 (Ch),  C.O.P.L.R. 348. So why is the statutory definition not used?
The purpose of the relevant sections of the Mental Capacity Act were to say when a living person could make decisions for themselves, and to set out how decisions should be made if that person was unable.
This is something completely different from looking retrospectively at whether a deceased person had mental capacity when they made their Will (which inevitably is what we need to do if we are considering challenging that Will). This type of retrospective evaluation is not within the scope of the Mental Capacity Act.
So what is the relevant test? The test can be found in a very old case – Banks v Goodfellow (1870) LR 5 QB 549, at page 565. This states that when a person makes their Will, they must:
- Understand what they are doing;
- Understand the extent of the property which they are giving away in the Will;
- Be able to understand and appreciate the claims to which they ought to give effect (for example, who they should at least think about when deciding where their assets should go – even if they don’t actually make a gift to that person); AND
- No insane delusion must influence their will in disposing of their property.
The Courts developed this test further in Key and another v Key and others  EWHC 408 (Ch) which confirmed that the testator should be able to exercise their powers of decision-making. Further, in Simon v Byford and others  EWCA Civ 280 the Court confirmed that the test related to the potential capacity to understand which did not equate with memory. This decision also confirmed that the testator must understand what he was disposing of, but not necessarily understand the collateral consequences of making such a disposition. In other words, it wasn’t a bar to capacity that the testator in that case had forgotten the reasons for the disposition in their earlier will and might not have appreciated the consequences of then changing that disposition.
It is presumed the testator has capacity
Where a Will is executed and attested properly, there is a presumption that the person making it has mental capacity. What does that mean? Essentially anyone making a challenge must bring evidence to show that they did not have capacity – otherwise it is assumed that they did. If however evidence is produced which goes against the presumption, the Court will then find the Will invalid unless evidence is also adduced to sufficiently affirm that the testator was indeed of sound mind (Symes v Green (1859) 1 Sw & Tr 401). The burden of proving capacity then shifts to those seeking for the Will to be accepted.
Note that where the Will has been made with the assistance of a solicitor who records that the testator had capacity, the standard of evidence required to show that they did not will need to be high (Hawes v Burgess and another  EWCA Civ 74)
What does this mean for you?
If you want to challenge the validity of a Will on the basis that when the testator made the Will, they did not have the required mental capacity (as set out in Banks v Goodfellow – see above) you will need to provide evidence. This evidence needs to relate to the time the person made the Will. Note that a diagnosis of dementia alone is not a bar to making a Will – dementia affect everyone differently and progresses at different paces. Someone in the early stages may well have the capacity to make a Will. However, a diagnosis might be part of the evidence that you present, alongside other evidence. Similarly, lack of a formal diagnosis is not a bar to challenging the Will – other evidence can be used to prove lack of capacity at the relevant time.