Legal Capacity


Hiring a lawyer, or proper execution of a legal instrument requires that the person signing have sufficient mental “capacity” to understand the implications of the engagement or the document. We will be using the following terms inter-changeably:

  • capacity / incapacity
  • capability / incapability
  • competence / incompetence

The Big Question

The big question for you in this area is how do you, as a lawyer or legal advocate, come to a reasonable belief that a client has diminished capacity?  Two specific and unavoidable capacity issues are does your client have the capacity to:

  • retain you for your services and instruct you?
  • complete the legal transaction?


Definitions of capacity vary across jurisdictions and have evolved over the years. It is now generally understood as the ability:

  • to understand the information you need to make a decision


  • to appreciate the consequences of making a decision

Process vs Outcome

In this sense capacity is about a person’s decision-making process, and it is neutral as to the outcome of that process. Therefore, all adults retain the right to make unwise or risky decisions, where they make these choices with capacity. This is regardless of age, disability or illness—even in the context of abuse.

Capacity Continuum

While people often speak of legal “capacity” or “competence” as an either/or thing–either the person is incompetent or they are competent–in fact it can be quite variable depending on the person’s abilities and the function for which capacity is required.  At Seniors First BC we speak of a ‘capacity continuum.’

capacity continuum

One side of the capacity equation involves the client’s abilities, which may change from day to day (or even during the day), depending on the course of the illness, fatigue and the effects of medication. On the other side, greater understanding is required for some legal activities than for others.

No Global Incapacity

There is no such concept as ‘total’ or ‘global’ legal incapacity resulting from mental disability.

“Incompetence is not to be understood in any global sense, but rather as reflecting incapacities with respect to specific decisions or areas of decision.” [emphasis added] (Ont. Enquiry on Mental Competency – Professor David Weisstub).

Causes of Incapacity

There is no illness that, of itself, will lead to a finding of incapacity (altho latter stage Alzheimer’s obviously will).

global capacity

Diminished capacity can arise as a result of:

    • Mental illness
    • Lack of mental development due to a birth defect
    • Brain damage at some point after birth
    • Extreme physical  impediments which prevent communication and understanding

We will be most concerned with brain damage due to dementia.  Older adults suffer more often from loss of mental capacity than any other age group because they are susceptible to dementia.  For more information on dementia, review our dementia webpage.  For more information on assessing capacity, see our assessing capacity webpage.