You’re staring at a fact pattern where someone just killed another person. Your instinct says “that’s murder”—but then you spot the twist. The defendant was being attacked. Or thought they were. Or maybe they were legally insane at the time. Suddenly, you’re not dealing with guilt or innocence anymore. You’re dealing with criminal defenses on the MBE, and these questions separate students who memorize from students who understand.
The bar examiners love criminal defenses because they test your ability to apply multi-layered analysis under pressure. A single fact pattern can implicate self-defense, imperfect self-defense, and voluntary manslaughter—all at once. Let’s break down how justification and excuse defenses actually work on the MBE, so you can spot them instantly and apply the right rule.
The Critical Distinction: Justification vs. Excuse
Here’s what trips up most bar takers: not all defenses work the same way. Some defenses say “the act was justified under the circumstances.” Others say “the defendant shouldn’t be held responsible because of their mental state or condition.”
Justification defenses claim the conduct was socially acceptable or necessary. Self-defense is the classic example. Society says you’re allowed to use reasonable force to protect yourself from imminent unlawful force. The act itself—using violence—is justified by the circumstances.
Excuse defenses admit the conduct was wrong but argue the defendant lacked the mental capacity to be held criminally responsible. Insanity is the textbook excuse defense. The defendant did commit the act, but their mental disease or defect means we don’t punish them the same way.
Why does this distinction matter on the MBE? Because the elements are completely different. Justification defenses focus on the reasonableness of the defendant’s actions in response to external threats. Excuse defenses focus on the defendant’s internal mental state and capacity.
Self-Defense on the Bar Exam: The Most Tested Justification
Self-defense appears in roughly one out of every three criminal law MBE questions involving violence. You need to know the elements cold, and you need to recognize the variations the examiners throw at you.
Self-defense allows a defendant to use reasonable force to protect themselves against what they reasonably believe is imminent unlawful force. Let’s unpack that:
The force must be reasonable. You can’t shoot someone who’s about to slap you. The force used must be proportional to the threat faced. Deadly force is only justified when the defendant reasonably believes they face imminent death or serious bodily injury.
The threat must be imminent. A threat to harm you next week doesn’t justify violence today. The attack must be happening now or about to happen immediately. This is where battered spouse cases get tricky on the MBE—if the defendant kills while the abuser is sleeping, traditional self-defense doesn’t apply because the threat wasn’t imminent.
The belief must be reasonable. Here’s the key: we judge reasonableness from the perspective of a reasonable person in the defendant’s situation. The defendant must actually believe force is necessary (subjective), and that belief must be objectively reasonable.
Consider this fact pattern: Defendant sees Victim reaching into his jacket pocket. Defendant, who has been threatened by Victim before, honestly believes Victim is reaching for a gun and shoots him. Victim was actually reaching for his phone. Is this self-defense?
It depends on whether a reasonable person in the defendant’s position would have believed Victim was reaching for a weapon. If yes, self-defense applies even though the defendant was factually wrong. The defense is judged by what the defendant reasonably believed, not by what was actually true.
Imperfect Self-Defense: When Honest Isn’t Reasonable
Now here’s where the MBE gets sneaky. What if the defendant’s belief was honest but not reasonable?
Imperfect self-defense applies when the defendant genuinely believed deadly force was necessary, but that belief was objectively unreasonable. In jurisdictions recognizing this doctrine, imperfect self-defense doesn’t provide a complete defense—but it does reduce murder to voluntary manslaughter.
The MBE loves this because it tests whether you understand the difference between complete defenses and mitigating doctrines. A defendant with imperfect self-defense still committed a homicide. The unreasonable belief doesn’t justify the killing. But because the defendant acted out of a genuine (if mistaken) belief in the need for self-protection, the law treats it as voluntary manslaughter rather than murder.
Watch for fact patterns where the defendant overreacts to an ambiguous situation. That’s your imperfect self-defense signal.
Defense of Others and Defense of Property
The MBE will test whether you know the limitations on these related justification defenses.
Defense of others follows the same rules as self-defense. You can use reasonable force to protect a third person from imminent unlawful force. Traditionally, you “stepped into the shoes” of the person you were defending—if they didn’t actually have a right to self-defense, neither did you. Modern rule: You’re judged by what you reasonably believed, even if the person you defended was actually the aggressor.
Defense of property never justifies deadly force. You can use reasonable non-deadly force to prevent the theft or destruction of your property, but you cannot kill someone to protect property. Spring guns and deadly traps are almost always unlawful for this reason.
The MBE will give you a fact pattern where someone shoots a fleeing thief. That’s not defense of property—the threat has passed, and deadly force was never justified to protect mere property anyway.
Insanity Defense on the MBE: Four Tests You Must Know
The insanity defense is the most commonly tested excuse defense, and the MBE makes it complicated by asking you to apply different tests in different questions.
M’Naghten Test (most common): The defendant is not guilty by reason of insanity if, at the time of the act, they suffered from a mental disease or defect that caused them either: (1) not to know the nature and quality of their act, or (2) not to know that their act was wrong. This is a cognitive test—did the defendant understand what they were doing and that it was wrong?
Irresistible Impulse Test: The defendant is insane if they had a mental disease or defect that prevented them from controlling their conduct, even if they knew it was wrong. This adds a volitional component—could the defendant stop themselves?
Durham Test (rarely used): The defendant is not guilty if their act was the product of mental disease or defect. This is the broadest test and is only used in a handful of jurisdictions.
Model Penal Code Test: The defendant is not guilty if, at the time of the act, they lacked substantial capacity either to appreciate the criminality of their conduct or to conform their conduct to the requirements of law. This combines cognitive and volitional elements.
The MBE will tell you which test to apply in the call of the question. Your job is to apply the facts to the correct standard. Watch for defendants who know their act is wrong but claim they couldn’t control themselves—that only works under tests that include a volitional component.
Intoxication: Voluntary vs. Involuntary
Voluntary intoxication is never a defense to general intent crimes or crimes with a malice or recklessness mens rea. It can negate the specific intent required for specific intent crimes, but only if the intoxication prevented the defendant from forming that intent.
Here’s the MBE trap: voluntary intoxication doesn’t give you a free pass just because you were drunk. It only matters if you were so intoxicated that you couldn’t form the specific intent the crime requires. If you intended to kill someone while drunk, you still had the intent to kill—voluntary intoxication doesn’t help you.
Involuntary intoxication occurs when the defendant didn’t know they were consuming an intoxicating substance or was forced to consume it. This is treated like a mental disease or defect and is analyzed under whichever insanity test the jurisdiction uses.
The MBE loves giving you a defendant who got drunk voluntarily and then committed a crime. Don’t overthink it. Unless the crime requires specific intent and the defendant was too intoxicated to form that intent, voluntary intoxication is irrelevant.
Duress: When Someone Made You Do It
Duress is an excuse defense that applies when the defendant committed a crime because they reasonably believed another person would imminently kill or seriously injure them or a family member if they didn’t comply. The threat must be of death or serious bodily harm—threats to property or reputation don’t qualify.
Duress is never a defense to intentional murder. You cannot kill an innocent person to save yourself. The MBE will test this repeatedly. Duress can reduce murder to manslaughter in some jurisdictions, but it won’t provide a complete defense.
The threat must be imminent and present. If the defendant had time to seek help from authorities, duress doesn’t apply.
Necessity: Choosing the Lesser Evil
Necessity (also called the “choice of evils” defense) applies when the defendant committed a crime to avoid a greater harm caused by natural forces or circumstances. Classic example: You break into a cabin during a blizzard to avoid freezing to death.
Necessity requires: (1) the defendant reasonably believed their action was necessary to avoid imminent harm, (2) there was no legal alternative, and (3) the harm avoided was greater than the harm caused.
Unlike duress, necessity can apply to any crime—but it’s very rarely successful for homicide. Courts generally hold that one human life is not more valuable than another, so you can’t kill one person to save another under necessity.
The MBE distinguishes duress from necessity by the source of the threat. If another person is threatening you, that’s duress. If natural forces or circumstances create the emergency, that’s necessity.
Mistake of Fact: When Being Wrong Matters
Mistake of fact can negate the mens rea required for a crime, but only if the mistake is reasonable and relates to an element of the offense.
For specific intent crimes, even an unreasonable mistake of fact is a defense if it negates the specific intent. For general intent crimes, only a reasonable mistake of fact is a defense.
For strict liability crimes, mistake of fact is never a defense. This is why statutory rape is such a harsh crime—even a reasonable belief that the victim was above the age of consent doesn’t matter.
The MBE will give you a defendant who made a mistake about a critical fact. Your job is to determine: (1) what mens rea does the crime require, and (2) does the mistake negate that mens rea?
How to Memorize Criminal Defenses for the MBE
Criminal defenses are tested through layered analysis. The examiners give you a fact pattern where multiple defenses might apply, then ask you to identify which one fits best or how each defense would affect the outcome.
You need to memorize the elements of each defense, but you also need to understand how they interact. Self-defense might fail, but imperfect self-defense might apply. Insanity might not work under M’Naghten, but it might under the Model Penal Code test.
This is where active recall makes the difference. You can’t just read through defenses and hope you’ll recognize them on test day. You need to practice applying them to fact patterns until the analysis becomes automatic.
If you want all the criminal defenses organized for exactly this kind of active recall, FlashTables covers every justification and excuse defense in the Criminal Law & Procedure subject, with each rule broken down into its testable elements. The two-column format puts the rule on the left and the elements on the right, so you’re forced to retrieve the information rather than passively re-reading outlines.
What to Memorize Right Now
Here’s your takeaway for criminal defenses on the MBE:
Self-defense: Reasonable force against imminent unlawful force based on a reasonable belief. Deadly force only for imminent death or serious bodily injury.
Imperfect self-defense: Honest but unreasonable belief—reduces murder to manslaughter in jurisdictions that recognize it.
Insanity: Know all four tests. M’Naghten is most common. The MBE will tell you which test to apply.
Voluntary intoxication: Only negates specific intent if the defendant was too intoxicated to form it. Never a defense to general intent crimes.
Duress: Imminent threat of death or serious bodily harm. Never a complete defense to intentional murder.
Necessity: Choice of evils from natural forces. Harm avoided must outweigh harm caused.
Mistake of fact: Negates mens rea for specific intent crimes (even if unreasonable). Must be reasonable for general intent crimes. Never works for strict liability.
Criminal defenses are where the MBE tests whether you actually understand criminal law or just memorized a list of crimes. Master the elements, practice the analysis, and you’ll spot these defenses instantly when they appear in fact patterns.