Also known as: mental deficiencies · mentally deficient · mental defect
Written by attorneys · grounded in primary & secondary sources — see below
A condition of impaired mental functioning that does not relieve an adult actor from liability for conduct falling below the standard of a reasonable person under like circumstances. The rule maintains an objective measure of care for all adults regardless of cognitive limitations.
Madison Meyers served as plant manager at a chemical facility and had a documented psychotic disorder causing distorted risk assessment. After receiving safety briefings that a pressure test was mandatory, she directed the crew to bypass it to meet a shipping deadline. The vessel ruptured and damaged an adjacent warehouse. Her mental condition supplied no defense because the conduct deviated from the standard of a reasonable person.
Marcus Mitchell inspected a home and observed clear water intrusion and mold but omitted any mention when completing disclosure forms for buyer Michelle Murphy. He later received a dementia diagnosis that impaired his recall. The omission breached the reasonable-agent standard. His undiagnosed condition did not lower the required level of care.
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Maurice Marshall owned a clothing store and received six direct complaints about a cracked entrance step over four months. He acknowledged each complaint yet posted no warning and made no repair. Customer Mason McCarthy tripped and broke his leg. Marshall's intellectual disability did not alter the objective standard applied to his inaction.
Mariam Mansour operated a crane at a construction site and had a documented intellectual disability. She misread hand signals and swung a load over a sidewalk, dropping debris that injured a pedestrian. The jury measured her conduct against that of a reasonable crane operator. The disability supplied no basis for a reduced standard.
Metro Bank employee Madison Meyers worked as a deckhand and misunderstood instructions due to an intellectual disability, leaving trucks improperly chocked. Rough seas shifted the cargo and injured a passenger. Her conduct was judged against the ordinary reasonable-person standard. The mental condition did not excuse or lower the required care.
Momentum Capital employee Marcus Mitchell processed a vision test at the motor vehicle office and had an intellectual disability. He recorded a failing score as passing, allowing an unqualified driver to obtain a license that later caused an accident. The court applied the unmodified reasonable-clerk standard. The disability did not modify the objective measure of care.
No. The law applies an objective reasonable-person standard to adults regardless of intellectual disability or other mental conditions. The rule treats mental deficiency differently from physical disabilities, which receive an adjusted standard.
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Physical disability triggers an adjusted standard measured by a reasonable person with the same physical limitation. Mental deficiency receives no such adjustment and the ordinary reasonable-person standard continues to apply.
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No. The rule focuses on whether the conduct conformed to the objective standard, not on the defendant's subjective capacity or knowledge of the condition. Undiagnosed mental deficiency supplies no defense.
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The rule prioritizes compensation for injured third parties and avoids difficult evidentiary inquiries into the precise effect of mental conditions. It also encourages treatment and workplace accommodations rather than reliance on the condition as a shield.
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…of a threat to the health or life of the mother, or that the child "may be born with incapacitating physical deformity or mental deficiency," or that a pregnancy "resulting from legally established statutory or forcible rape or incest may constitute a threat to the mental or physical health of the patient," two other physicians…