What legal principle does the defense of insanity invoke?

The defense of insanity invokes the legal principle of lack of accountability due to mental health status. This principle is rooted in the understanding that individuals who are mentally ill may not possess the capacity to understand the nature or wrongfulness of their actions at the time the crime was committed. This concept is often associated with the M'Naghten Rule, which states that a person may be excused from legal responsibility if, due to a severe mental disorder, they did not know the nature of the act or did not know that the act was wrong. The essence of this principle is that mental health can significantly impair judgment and decision-making, leading to a diminished capacity for criminal intent.

When an individual successfully establishes an insanity defense, it recognizes their lack of culpability in the eyes of the law, emphasizing the need for treatment rather than punishment. This legal framework acknowledges that mental illness can create a barrier to moral responsibility, and thus the legal system accommodates this by allowing for alternative routes such as mental health evaluations and treatment instead of traditional sentencing.