Also known as: sanely · sanity · sound mind · mental capacity
Written by attorneys · grounded in primary & secondary sources — see below
The mental condition of possessing a sound mind capable of understanding the nature and consequences of legal acts and forming the intent required for criminal liability. This condition is assessed at the precise time of the relevant act or transaction.
Sabrina Shah, recovering from surgery and taking pain medication, executed an irrevocable assignment of her entire portfolio to a high-risk hedge fund. Her spouse had no independent income and pending long-term care needs. The transfer placed both her future security and that of her dependent at substantial risk, so the assignment was invalid for lack of capacity.
Seth Shapiro, an eighty-eight-year-old resident of an assisted-living facility, signed a will naming a new acquaintance as primary beneficiary instead of his grandchildren. He occasionally misidentified relatives and properties during the meeting. Because he lacked the ability to know in a general way the natural objects of his bounty and relate them to his property, the will was invalid.
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Samuel Soto consumed hard cider and marijuana throughout the afternoon before participating in a marriage ceremony. He laughed inappropriately and required repeated prompting to recite his lines. Because he could not understand the nature of the legal act at the moment of the ceremony, the marriage was invalid for lack of capacity.
Sylvia Santos executed an irrevocable deed transferring an income-producing apartment building to a company formed by her caregiver's son. She relied on the rental income as her primary support and occasionally confused tenants and family members. The transfer jeopardized her future financial security, rendering the deed invalid.
Spencer Silver selected a deadly weapon, concealed himself to obtain an opportunity, and carried out a premeditated attack resulting in death. Evidence showed he understood the nature of his actions and the wrongfulness of killing. Because he possessed the mental capacity to form wilfulness and malice aforethought, he was held criminally responsible.
Sarah Sullivan, diagnosed with schizophrenia, was arrested and interrogated. Medical evaluation confirmed she remained alert, oriented, intelligent within normal limits, and sane within the legal definition. Because she possessed the mental capacity to understand her rights and the consequences of speaking, her detailed confession was admissible.
An individual eighteen or more years of age who is of sound mind may make a will. Sound mind requires the ability to know in a general way the nature and extent of property, the natural objects of bounty, and the disposition being made.
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The donor must possess the mental capacity necessary to make or revoke a will and must also understand the effect the gift may have on the donor's future financial security and that of anyone dependent on the donor.
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Capacity is determined at the precise time of the marriage ceremony. A party under the influence of alcohol or drugs may lack the mental capacity to understand the actions and agree to them.
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A person is presumed sane and capable of intending the natural and probable consequences of acts. This presumption may be rebutted by evidence that the defendant lacked the mental capacity to form the required intent or to know the wrongfulness of the conduct.
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A person incurs only voidable duties when, because of mental illness or intellectual disability, the person cannot reasonably understand the nature and consequences of the transaction or act in a reasonable manner regarding it, and the other party has reason to know of the condition.
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…Miranda was "alert and oriented as to time, place, and person," intelligent within normal limits, competent to stand trial, and sane within the legal definition. At the police station, the victim picked Miranda out of a lineup, and two officers then took him into a separate room to interrogate him, starting about 11:30…