By Corcoran Smith Law Corp. · Published · Updated
Lack of Capacity in California
California presumes everyone has capacity. To set aside a will or trust for incapacity the evidence must connect a listed mental-function deficit to the act and show significant impairment of the ability to understand and appreciate its consequences. The applicable standard, including section 6100.5 for wills, also matters. A dementia diagnosis alone does not meet the test.
The presumption runs against you, and the statute says why
California starts from the opposite of what most families assume. Probate Code section 810 declares a rebuttable presumption affecting the burden of proof that all persons have the capacity to make decisions and to be responsible for their acts, and states expressly that a person with a mental or physical disorder may still be capable of executing wills or trusts. It goes further: a determination of incapacity should rest on evidence of a deficit in one or more mental functions rather than on a diagnosis. Section 811 then supplies the structure: a finding must be supported by evidence of a deficit in at least one listed mental function — alertness and attention, information processing, thought processes, or mood and affect — and by evidence of a correlation between that deficit and the act in question. Under section 811(b), the deficit must significantly impair the ability to understand and appreciate the consequences of the person’s actions for that type of act or decision. For wills, section 6100.5 sets the standard: the individual must understand the testamentary act, recollect the nature and situation of their property, and understand their relations to those affected.
Sources: Probate Code s.810 - Presumption of capacity · Probate Code s.811 - Mental function deficits and the required correlation · Probate Code s.6100.5 - Capacity to make a will · Verified 2026-08-17.
What section 811 actually lists
| Mental function | Examples the statute gives |
|---|---|
| Alertness and attention | Level of arousal or consciousness; orientation to time, place, person and situation; ability to attend and concentrate |
| Information processing | Short- and long-term memory; ability to understand or communicate; recognition of familiar persons and objects; ability to understand quantities; ability to reason logically |
| Thought processes | Severely disorganised thinking; hallucinations; delusions; uncontrollable, repetitive or intrusive thoughts |
| Mood and affect | A pervasive, persistent or recurrent state such as euphoria, anger, anxiety, fear, panic, depression, hopelessness, helplessness or apathy, inappropriate in degree to the circumstances |
Correlation is where these cases are won and lost
Families routinely arrive with a diagnosis and expect it to be decisive. It is not, and section 810 says so directly. The work is connecting a specific deficit to the specific act — that the memory failure meant they could not recollect what they owned, or that a documented delusion about a particular child is what produced the disinheritance. Section 6100.5 also reaches that second situation independently: a will is invalid where a mental health disorder producing delusions or hallucinations caused the person to devise property in a way they otherwise would not have.
Capacity is only one of the questions a will can raise. Whether it was signed and witnessed properly is a separate one, answered by what makes a will valid in California.
Capacity and undue influence are different claims
They are frequently pleaded together and are often confused. Incapacity says the person could not form the intention. Undue influence says they could, but someone else’s pressure supplanted it. A person with full capacity can be unduly influenced, and the evidence that supports one claim frequently supports the other — which is why the two are usually investigated as one exercise.
Related: contesting a will, contesting a trust, undue influence, and lifetime transfers a contest cannot reach.
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A contingency fee means the attorney is paid from what is recovered rather than by the hour, so a beneficiary who cannot fund litigation out of pocket can still bring a claim. California regulates these agreements closely. Under Business and Professions Code section 6147, the agreement must be in writing and the attorney must give the client a duplicate copy, signed by both, when the contract is made. It must state the agreed contingency rate; how disbursements and costs incurred in prosecuting or settling the claim will affect that fee; and to what extent the client could be required to pay for related matters. Unless the matter falls under section 6146, the agreement must also state that the fee is not set by law and is negotiable. These are not formalities: failure to comply with any provision of section 6147 makes the agreement voidable at the client’s option, leaving the attorney entitled only to a reasonable fee.
Sources: Business and Professions Code s.6147 - Contingency fee contracts · Verified 2026-08-03.
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Call Anytime — Answered 24/7 · (213) 695-7353The Probate Code sections behind this page
Each section links to its official text at the California Legislature’s own site. The full index of sections covers the rest of the Code.
- Probate Code section 810
- Presumption of capacity. Read section 810
- Probate Code section 811
- Mental function deficits and the required correlation. Read section 811
- Probate Code section 812
- General standard of capacity to make a decision. Read section 812
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