Judges and lawyers are sometimes misled in their approach to testamentary capacity. They view it as if it were a medical diagnosis instead of a practical determination. The fact that it is a practical determination has been decided time and again in the case law, including in Banks v. Goodfellow[1] itself.

More recent courts have articulated this point in contemporary language. In Danchuk v. Calderwood,[2] Justice Harvey found:

Whether the testator’s mind was sound is a practical question. It does not depend on scientific or medical definition. Medical evidence is not required nor necessarily conclusive when given. The question may be answered as well by laymen of good sense.

In Stevens v. Crawford,[3] the Alberta Court of Appeal stated:

Put simply, testamentary capacity is possible even where the testator has a disease of the mind. While medical or scientific evidence may be of assistance, the finding of testamentary capacity is a matter of fact for the trial judge to determine.

This issue is important not only on an academic level but on a practical one. Counsel must remember that when going to trial on cases involving issues of testamentary capacity, both lay and medical witnesses should be called in order to establish, or rebut, a testator’s testamentary capacity.