A more thorough explanation:

MPC Test

The MPC Test is a legal test used in criminal law to determine if a person is criminally responsible for their actions. It is also known as the Substantial-Capacity Test. According to this test, a person is not responsible for their actions if they lack substantial capacity due to a mental disease or defect to either appreciate the criminality of their conduct or to conform their conduct to the law. This test combines elements of both the McNaghten rules and the irresistible-impulse test by allowing consideration of both volitional and cognitive weaknesses.

One example of the MPC Test being used is in the case of John Hinckley, who attempted to assassinate the President of the United States. He was found not guilty by reason of insanity using the MPC Test. However, since then, many jurisdictions have narrowed the insanity defense and adopted a new test resembling the McNaghten rules.

The MPC Test is used to determine if a person is responsible for their actions in criminal law. The example of John Hinckley illustrates how the MPC Test was used to find him not guilty by reason of insanity. However, since then, many jurisdictions have changed their laws to make it harder to use the insanity defense. This shows how the MPC Test has influenced the legal system and how it continues to be debated and changed over time.