There is no single legal definition of mental capacity in Western Australia. As a lawyer specializing in guardianship cases, this question is frequently top-of-mind when dealing with some of my clients.

It is important to understand the nuances of determining mental capacity in legal matters. The definition varies depending on the type of decision or transaction involved.

There are various legal tests for mental capacity, such as the test for testamentary capacity.

Despite the many different legal tests, the fundamental issue is whether the client is able to understand the general nature of what they are doing. If there is ongoing difficulty in this level of understanding it may indicate a lack of mental capacity which requires further exploration by the lawyer.

Any work done for a client who it later turns out lacked mental capacity could be invalid and expose the lawyer to potential legal and ethical issues.

For example, a client may appear to have the mental capacity to create a will, but in reality, they may be suffering from dementia and unable to understand the consequences of their actions. This could lead to the will being challenged and the lawyer facing potential legal repercussions.

Another example is, a client may not have the mental capacity to make a contract, but have mental capacity to make a will. A lawyer should be aware of this and should not proceed with the contract if they suspect the client lacks mental capacity. If a lawyer fails to do so, it could lead to the contract being challenged and the lawyer facing potential legal repercussions.

See a publication produced by The Law Society of New South Wales entitled “When a client’s mental capacity is in doubt – A practical guide for solicitors”, dated 2016" for more information.