Also known as: mental defects · mental deficiency
Written by attorneys · grounded in primary & secondary sources — see below
A mental condition of illness or cognitive impairment. In tort law the condition does not relieve an adult actor from liability for conduct that falls below the standard of a reasonable person under like circumstances.
Marcos owns a retail store and receives repeated complaints that the entrance step is crumbling. He takes no action to repair or warn customers. When Lena trips and breaks her leg, Marcos's documented intellectual disability does not lower the standard applied to his conduct.
Jordan, a city bus driver with a history of psychogenic blackouts, feels disoriented during his route yet keeps driving. He later blacks out and collides with Alex's car. Jordan's mental condition supplies no defense to the claim that he failed to meet the ordinary reasonable-driver standard.
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Chapman owns a store and ignores repeated warnings that a display case is unstable. A customer is injured when it falls. Chapman's evidence of mental defect does not alter the reasonable-person standard applied to her failure to act.
A physician owns a clinic and fails to warn patients of a known hazard in the waiting-room floor. A visitor is injured. The physician's mental defect supplies no defense to the claim that conduct fell below the reasonable-person standard.
Alexander operates a vehicle despite known cognitive impairment and causes a collision. The injured party sues in negligence. Alexander's mental defect does not lower the ordinary reasonable-driver standard of care.
The Tison brothers manage a property with a known dangerous condition and take no steps to remedy it. A visitor is injured. Their mental limitations do not relieve them from liability measured by the reasonable-person standard.
No. An adult with mental illness or cognitive impairment remains subject to the ordinary reasonable-person standard. The rule preserves an objective benchmark that protects injured third parties and avoids difficult inquiries into degrees of impairment.
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Physical disability receives an individualized standard that asks what a reasonable person with the same disability would have done. Mental deficiency receives no such adjustment for adults. The objective reasonable-person standard continues to apply.
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The rule prioritizes compensation for victims who cannot evaluate an actor's hidden limitations. It also promotes predictability, encourages treatment and accommodations, and avoids complex evidentiary disputes over the precise effect of any given mental condition.
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Yes. The absence of a prior diagnosis does not change the analysis. The objective standard focuses on whether the conduct conformed to that of a reasonable person, not on the defendant's subjective awareness of any impairment.
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…California Supreme Court noted that Chapman, against whom the evidence was less strong, had keyed her defense to evidence of her mental defect, a subject upon which the comment had not touched. From this discriminating analysis it was concluded that another result was not "reasonably probable" absent the erroneous comments. I…