Some courts have said that testamentary capacity is not a memory test, but in a very real way it is exactly that. Memory is a key component. That point was made in a line of historical cases beginning with the 1833 Scottish decision Simpson v. Gardners Trustees[1] which referred to memory as ‘the grand criterion’:

…the grand criterion by which to judge whether [the mind is]… injured or destroyed, is to ascertain the state of the memory. It is memory that affords us all the materials on which to exercise judgment, and to arrive at a conclusion or resolution. Without memory the mind cannot act, and it is the first of the intellectual faculties which fails, where the mind is in a state of decay.

The above passage entered Canadian jurisprudence in the 1914 decision of the Ontario Court of Appeal, Murphy v. Lamphier[2], and has been repeated in subsequent decisions including Pocock v. Pocock[3], Re Davis[4] and Coughlan Estate, (Re)[5].

The emphasis on memory is consistent with the most often quoted test for capacity which is found in Banks v. Goodfellow since that test cannot be satisfied without an ability to recollect one’s assets and heirs.

Despite its importance, memory has never been the only criterion relevant to the capacity to make a will and there are a number of ways in which an individual can lack this capacity without suffering memory problems. For example, one may lack capacity due to delusions or disorders of the mind. Further, in order to make a valid will one must be able to know the objects of one’s bounty and this requires both memory and judgment. It is also true that one’s memory does not have to be perfect for a finding of testamentary capacity to be made. Memory remains however the ‘grand criterion’ and is a necessary precondition for a finding of testamentary capacity when a will is challenged.