In Alberta, a person’s capacity to do a will, assuming capacity is an issue, is determined after the fact by a court. The legal test comes from the case of Banks v. Goodfellow. Essentially, the person doing a will (the testator) has to understand the consequences of doing a will, they have to, broadly speaking, understand what property is being disposed of in the will, they have to have an awareness of the people who would ordinarily expect to receive something from the estate (such as a spouse or partner, children, etc.), and they can’t be suffering from a condition that overrides their normal values and significantly clouds their judgement about their loved ones.
In the past, lawyers might discourage people with capacity concerns from even doing wills. Now it’s generally understood that lawyers shouldn’t be acting as judges. Clients with ambiguous capacity concerns should still be given the opportunity to do wills, but the lawyer should keep detailed notes so that a court can later decide on the capacity issues.
Obviously, if a person has severe dementia, to the point that they don’t know who is in their family, or perhaps to the point that they can’t even communicate, then a new will is inappropriate. Also, it should be noted that a family member or an attorney appointed under an enduring power of attorney cannot direct a lawyer to change another person’s will. If a person lacks capacity to complete a will, either a previously existing last will and testament will stand, or if the person never completed a will, then the provisions of the Wills and Succession Act that deal with intestacy (when a person doesn’t have a will) will apply.