I am regularly asked by family members if a parent has the mental capacity to make a new Will. So here is my answer in a nutshell.
Mental capacity is both time and task-specific. The level of capacity required when it comes to the requisite capacity to provide instructions for and to execute a valid Will is relatively high. We refer to this kind of mental capacity as “testamentary capacity”.
Courts frequently defer to the following test for testamentary capacity. It is a very old test from a very old case called Banks v. Goodfellow (1870) L.R. 5 Q.B. 549 from the courts of England:
the testator must understand the nature of the act and its effect;
the testator must understand the extent of his or her property;
the testator must be able to understand and appreciate the claims that may be made in respect of his or her property; and
there must be no “disorder of the mind” that prevents the exercise of his or her natural faculties.