Diminished Capacity Definition and Legal Meaning

On this page, you'll find the legal definition and meaning of Diminished Capacity, written in plain English, along with examples of how it is used.

What is Diminished Capacity?

n. A psychological term that is used in criminal trials to refer to the accused not being insane, but being under emotional distress, physical conditions or factors that affected their ability to fully comprehend the nature of their actions. In an attempt to remove the element of premeditation or criminal intent, it is raised by the defense to obtain a conviction for a lesser crime. For example: manslaughter instead of murder. Juries have been overly impressed by psychiatric testimony. A notorious instance was in People v. Dan White, the admitted killer of Sand Francisco Mayor George Moscone and Supervisor Harvey Milk. White received a manslaughter conviction on the basis that he had diminished capacity due to the sugar content of his blood which was due to eating “Twinkies.”

History and Meaning of Diminished Capacity

Diminished capacity is a legal defense that originated in the United States in the early 20th century. The theory behind this defense is that the accused should not be held fully responsible for their actions due to some sort of mental impairment or emotional distress. This impairment may preclude the accused from fully understanding the nature of their actions, the wrongfulness of their actions, or from forming the requisite intent to commit a crime. Over time, the definition of diminished capacity has evolved and its application in criminal trials has been controversial.

Examples of Diminished Capacity

  1. A person with a history of mental illness kills their neighbor after becoming convinced that the neighbor is part of a vast conspiracy to harm them. The defense raises the argument of diminished capacity to reduce the charge from murder to manslaughter.
  2. In a case of vehicular homicide, the accused claims that they were under the influence of prescription medication that impaired their ability to drive. The defense raises the argument of diminished capacity to reduce the charge to a lesser offense.
  3. A person with a low IQ is accused of participating in a robbery. The defense raises the argument of diminished capacity to argue that the accused did not fully comprehend the criminal nature of their actions.

Legal Terms Similar to Diminished Capacity

  1. Insanity defense - A legal defense that asserts that the accused should not be held responsible for their actions due to mental illness or defect.
  2. Automatism - A defense that asserts that the accused committed a criminal act without the control of their actions due to an involuntary bodily movement or other circumstance.
  3. Guilty but mentally ill - A verdict that acknowledges the defendant’s guilt and account for their mental illness or emotional distress.