General principles - Mental disorder

Learning Outcomes

After reading this article, you will be able to identify when mental disorder is relevant to criminal liability on the MBE. You will understand the main insanity tests, the difference between insanity and diminished capacity, and the requirements for fitness to stand trial. You will be able to apply these principles to MBE-style questions and avoid common pitfalls.

MBE Syllabus

For the MBE, you are required to understand how mental disorder affects criminal responsibility and procedure. This includes:

  • Recognizing when insanity is a defense to criminal charges and knowing the main insanity tests (M'Naghten, Irresistible Impulse, Durham, and Model Penal Code).
  • Distinguishing insanity from diminished capacity and intoxication.
  • Understanding the burden of proof and procedural requirements for raising insanity.
  • Knowing the rules for fitness to stand trial (competency) and the consequences of incompetency.
  • Identifying when mental disorder is relevant to sentencing or post-trial procedures.

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

  1. Which of the following is NOT a recognized test for insanity on the MBE?
    1. M'Naghten test
    2. Irresistible impulse test
    3. Substantial capacity test (Model Penal Code)
    4. Reasonable person test
  2. If a defendant is found not guilty by reason of insanity, the usual result is:
    1. Immediate release
    2. Civil commitment until no longer dangerous
    3. Mandatory life imprisonment
    4. Automatic retrial
  3. Which statement best describes the difference between insanity and diminished capacity?
    1. Insanity is a procedural issue; diminished capacity is a defense to liability.
    2. Insanity is a complete defense; diminished capacity may negate specific intent.
    3. Both are complete defenses to all crimes.
    4. Diminished capacity applies only to strict liability offenses.
  4. Which party generally bears the burden of proving insanity on the MBE?
    1. The prosecution, beyond a reasonable doubt
    2. The defendant, by a preponderance of the evidence or clear and convincing evidence
    3. The judge, by judicial notice
    4. The jury, by majority vote

Introduction

Mental disorder can affect criminal liability and procedure in several ways. The most important for the MBE are the insanity defense, diminished capacity, and the requirement that a defendant be fit (competent) to stand trial. These doctrines are tested regularly and require careful attention to the specific legal standards and burdens of proof.

Insanity as a Defense

Insanity is a complete defense to criminal liability if, at the time of the offense, the defendant met the legal test for insanity. The MBE may test any of the four main insanity tests:

Key Term: Insanity (Legal) A legal defense excusing criminal responsibility if, at the time of the offense, the defendant met a recognized test for insanity.

Key Term: M'Naghten Test The defendant is insane if, due to a mental disease or defect, they did not know the nature and quality of the act or did not know it was wrong.

Key Term: Irresistible Impulse Test The defendant is insane if, due to mental illness, they could not control their actions or conform their conduct to the law.

Key Term: Durham Test The defendant is insane if the unlawful act was the product of a mental disease or defect.

Key Term: Model Penal Code (Substantial Capacity) Test The defendant is insane if, due to mental disease or defect, they lacked substantial capacity either to appreciate the criminality (wrongfulness) of their conduct or to conform their conduct to the law.

Burden of Proof

On the MBE, the defendant generally bears the burden of proving insanity, either by a preponderance of the evidence or by clear and convincing evidence, depending on the jurisdiction. The prosecution must prove all elements of the offense, but does not have to disprove insanity unless the defendant raises it.

Consequences of a Successful Insanity Defense

A verdict of not guilty by reason of insanity usually results in civil commitment until the defendant is no longer dangerous due to mental illness.

Diminished Capacity

Diminished capacity is not a complete defense, but may prevent conviction for specific intent crimes if the defendant, due to mental disorder, could not form the required intent.

Key Term: Diminished Capacity A partial defense where mental disorder short of insanity prevents the defendant from forming the specific intent required for certain crimes.

Diminished capacity is not recognized in all jurisdictions and does not apply to general intent or strict liability offenses.

Fitness to Stand Trial (Competency)

A defendant must be competent to stand trial. This means they must understand the proceedings and be able to assist in their defense.

Key Term: Fitness to Stand Trial (Competency) The requirement that a defendant have sufficient present ability to consult with counsel and understand the proceedings against them.

If a defendant is found incompetent, the trial is postponed until competency is restored. Incompetency is not a defense to the crime itself.

Intoxication and Mental Disorder

Intoxication is not a mental disorder, but voluntary intoxication may sometimes negate specific intent. Involuntary intoxication may be treated like insanity if it produces a mental state meeting the insanity test.

Key Term: Involuntary Intoxication Intoxication not self-induced, such as by force, fraud, or unforeseen reaction to medication, which may excuse criminal liability if it produces insanity.

Worked Example 1.1

A defendant is charged with murder. At trial, he presents evidence that, due to schizophrenia, he believed he was squeezing a lemon, not a person's neck, when he strangled the victim. The jurisdiction applies the M'Naghten test.

Answer: Under the M'Naghten test, the defendant is insane if, due to mental disease, he did not know the nature and quality of his act. Here, if the jury believes he thought he was squeezing a lemon, he did not know the nature of his act and should be found not guilty by reason of insanity.

Worked Example 1.2

A defendant is charged with burglary, a specific intent crime. He suffers from a personality disorder that impairs his judgment but does not meet the legal test for insanity. He argues he could not form the intent to commit a felony inside the building.

Answer: If the jurisdiction recognizes diminished capacity, and the jury finds the defendant's mental disorder prevented him from forming the specific intent for burglary, he may be acquitted of burglary but could still be convicted of a lesser general intent offense.

Worked Example 1.3

A defendant is charged with assault. Before trial, his attorney moves for a competency hearing, arguing the defendant cannot understand the proceedings or assist in his defense.

Answer: If the court finds the defendant incompetent to stand trial, the trial is postponed until competency is restored. This does not bar prosecution if competency is later regained.

Exam Warning

The insanity defense is rarely successful and is only available if the defendant meets the legal test at the time of the offense. Mental illness alone does not equal legal insanity. Always apply the specific test given in the question.

Revision Tip

On the MBE, pay close attention to whether the question is about insanity (at the time of the offense), diminished capacity (specific intent), or competency (fitness to stand trial). Do not confuse these doctrines.

Key Point Checklist

This article has covered the following key knowledge points:

  • Insanity is a complete defense if the defendant meets a recognized legal test at the time of the offense.
  • The four main insanity tests are M'Naghten, Irresistible Impulse, Durham, and Model Penal Code (substantial capacity).
  • The defendant usually bears the burden of proving insanity.
  • Diminished capacity may negate specific intent but is not a complete defense.
  • Fitness to stand trial (competency) is required for trial to proceed; incompetency postpones but does not bar prosecution.
  • Involuntary intoxication may excuse liability if it produces insanity.
  • Not guilty by reason of insanity usually leads to civil commitment, not immediate release.

Key Terms and Concepts

  • Insanity (Legal)
  • M'Naghten Test
  • Irresistible Impulse Test
  • Durham Test
  • Model Penal Code (Substantial Capacity) Test
  • Diminished Capacity
  • Fitness to Stand Trial (Competency)
  • Involuntary Intoxication
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