What is "Diminished Capacity" in Criminal Law?

You will often hear of a defendant pleading "diminished capacity" to a crime, which is different from pleading insanity. Diminished capacity means that the defendant is guilty of the crime, but to a lesser offense. In criminal law, there are two factors used to determine guilt: actus reus, which refers to the act of the crime itself; and mens rea, which refers to the mental state prior to and during the commission of a crime. Diminished capacity deals exclusively with mens rea.

If you plead "diminished capacity" in criminal law, you acknowledge that you committed the crime, but claim that mitigating factors rendered you incapable of possessing the mental capacity needed to commit the crime on the offense with which you are charged. For example, if you are charged with murder in the first degree, you might claim diminished capacity to reduce the charges to manslaughter in the second degree.

"Diminished capacity" has sparked much controversy in criminal law because there is no clear definition as to what might constitute the defense. You've probably heard of the "Twinkie defense", which goes back to a 1979 California case (People v. White) in which a former city employee shot and killed two people, but claimed that his high intake of junk food combined with his depression over being fired created diminished capacity.

This case in particular enraged the public because the jury bought the defense, and "diminished capacity" has since been ridiculed by many activist groups and prosecutors. However, it still exists today, depending on the crime committed. If there are mitigating factors that might have influenced the defendant outside of his control, he may be found guilty of a lesser charge.