Insanity Defenses (and How I Keep Them Straight)

There are several different tests for insanity, and they can be easily confused. That’s why it’s sometimes an examiners’ favorite. You have to know the different approaches. Here’s a shorthand way:

Under the M’Naghten rule, because of a mental impairment, the defendant doesn’t know right from wrong or doesn’t understand the nature and quality of his actions.

Here’s how I remember this test: The M’Naughten rule is sometimes referred to as the McNaghten rule, which reminds me of McDonald’s. My kids love McDonalds, as do I. We simply don’t know right from wrong, and we may not understand the impact of our actions. I refuse to watch Super Size Me.

For the irresistible impulse test, it’s just like the name says: the defendant just could not resist the impulse to act. Said another way, the defendant was unable to control his actions or to conform his conduct to the law.

How do I remember this test? The name of the test makes it obvious.

For the Durham test, you have to find that “but for the mental illness, the defendant would not have done the act.”

How do I remember this test? The name of this test reminds me of the 1988 rom-com sports flick, Bull Durham, starring Kevin Costner, Susan Sarandon, and Susan Sarandon’s former partner, Tim Robbins. If you’re not familiar with the movie, it’s basically a mature comedy about sex and baseball. There’s one scene in the movie where Costner slaps Robbins on the butt. Sixteen-year-old me (the age when I likely saw the movie in 1988) thought that scene was hilarious. So, “butt” equals “but” equals “but for” equals “Bull Durham” equals “Durham test.”

Finally, you have the MPC test—think of it as a combination of M’Naghten and irresistible impulse. Under the MPC test, as the result of a mental impairment, the defendant doesn’t know right from wrong or understand his actions or he was unable to control his actions or conform his conduct to the law.

How do I remember this test? MPC is combination of letters, so the test is a combination of the M’Naghten and irresistible impulse tests. The MPC doesn’t include the Durham test because (Bull) Durham is in a league of its own (to use another baseball reference).