A justification defense deems conduct that is otherwise criminal to be socially acceptable and non-punishable under the specific circumstances of the case. Justification focuses on the nature of the conduct under the circumstances.
Examples include:
• Self-defense
• Defense of others
• Defense of property and habitation
• Use of lawful force
• Necessity
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Excuse defenses focus on the defendant’s moral culpability or his ability to possess the requisite mens rea. An excuse defense recognizes that the defendant has caused some social harm but that he should not be blamed or punished for such harm.
Examples include:
• Duress
• Insanity
• Diminished capacity
• Intoxication (in very limited circumstances)
• Mistake of fact
• Mistake of law (in very limited circumstances)
Justification and excuse defenses apply to all crimes. Some defenses, however, pertain to just one or a few crimes. For example, “legal impossibility” is a common law defense to the crime of attempt.
Justification, excuse, and offense-modification defenses all relate to the defendant’s culpability or to the wrongfulness of his conduct. In contrast, extrinsic or non-exculpatory defenses bar conviction, or even prosecution, based on factors unrelated to the defendant’s actions or state of mind at the time of commission. Examples of such defenses are statutes of limitations, diplomatic immunity, and incompetency to stand trial.