Okay, here's another one of those posts that is written for people curious about a forensic psychology topic that often makes the news, but that people don't know all that much about. In addition, I'd be happy to answer any questions about the topic, since many people find "not guilty by reason of insanity pretty interesting," and yet the people in the news (or in TV, movies, etc.) usually do a horrible job portraying the issue.
Generally speaking, in order to consider that an individual is guilty of committing a crime, there must be proof of two elements: 1) the individual engaged in unlawful conduct (actus reus); and 2) the individual did so with unlawful intent (mens rea). The degree, or amount, of intent is usually included in the description of the offense. For example, there are differing levels of intent necessary for the commission of involuntary manslaughter versus first degree murder.
The second prong noted above (mens rea) presumes that people act with free will (now, I know this is a debate that has raged forever, and will likely be never be settled, but from a legal standpoint this larger debate doesn’t matter). The law does recognize, however, that while most of us choose our own behavior, and are therefore responsible for it, some individuals are incapacitated due to mental illness to the extent that their free will is impaired.
Broadly speaking, the first type of mental illness that can be considered to potentially impair free will would be mental illnesses that impair cognitive functioning. This would be the sort of mental illness that impairs an individual’s ability to make rational, informed decisions based on a reasonable understanding of the world. For example, an individual with an IQ of 45 would almost certainly be considered cognitively impaired to the point where mens rea would not be assumed. That is, due to severe cognitive limitations, that individual would not be considered able to grasp the world in such a manner that unlawful intent would be ascribed to him or her. A non-mental health way of looking at this would be how we would address a crime committed by a five-year old. We simply don’t hold a five-year old to the same standards as an adult, because their capacity to understand the world and reality is significantly limited.
In another post, I’ll address the second aspect of a limitation on free will. In addition, I will post an analysis of this issue with respect to Josef Fritzl, the Austrian guy who kept his daughter locked in his basement for 20 years...