Under the M'Naghten rule, which criterion is primarily used to determine whether a defendant can be found not guilty by reason of insanity?

• A. Whether the defendant was experiencing hallucinations at the time of the crime
• B. Whether the defendant was unable to understand the nature and quality of the act or that it was wrong due to a mental disorder
• C. Whether the defendant was diagnosed with a personality disorder
• D. Whether the defendant had a history of substance abuse

Answer: (B)

Verified step by step guidance

1. Understand that the M'Naghten rule is a legal standard used to assess criminal responsibility in cases involving insanity.
2. Recognize that the key criterion under the M'Naghten rule focuses on the defendant's cognitive ability at the time of the crime.
3. Specifically, the rule asks whether the defendant was unable to understand the nature and quality of their act or did not know that the act was wrong due to a mental disorder.
4. Note that experiencing hallucinations, having a personality disorder, or a history of substance abuse are not the primary criteria under this rule, although they may be relevant in other contexts.
5. Therefore, the main test is about the defendant's mental state in terms of understanding their actions and their wrongfulness at the time of the offense.