MPC § 3.05: Use of Force for the Protection of Other Persons
What does Use of Force for the Protection of Other Persons (Model Penal Code) provide?
Section 3.05 extends the self-defense principles of Section 3.04 to the protection of third parties. The actor is justified in using force to protect another person when they believe such force is immediately necessary to protect the other person against unlawful force and the actor believes that the circumstances are such that the protected person would be justified in using such protective force, and the actor believes their intervention is necessary.
Source: Model Penal Code § 3.05
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Summary
Section 3.05 extends the self-defense principles of Section 3.04 to the protection of third parties. The actor is justified in using force to protect another person when they believe such force is immediately necessary to protect the other person against unlawful force and the actor believes that the circumstances are such that the protected person would be justified in using such protective force, and the actor believes their intervention is necessary.
The MPC's approach allows the defender to use the same degree of force that the protected person would be entitled to use in self-defense. If the protected person would be justified in using deadly force, the defender may also use deadly force. The limitations on force from Section 3.04 carry over: the duty to retreat (the actor must attempt to secure the protected person's retreat if possible), the ban on deadly force by an initial aggressor, and the proportionality requirements.
Critically, the MPC takes a subjective approach to defense of others: the actor is judged based on what they believe about the situation, not on the actual facts. If the actor honestly but mistakenly believes the person they are defending is being unlawfully attacked, the defense is available (subject to the Section 3.09 limitations on reckless or negligent mistakes). This contrasts with the older common law "alter ego" rule.
Key Provisions
5 essential provisions of § 3.05
Force justified when actor believes it is immediately necessary to protect another against unlawful force
Actor must believe the protected person would be justified in using self-defensive force under the circumstances
Actor must believe their intervention is necessary for the other person's protection
Same limitations as self-defense apply: retreat duty, proportionality, and initial aggressor rules
Subjective belief standard: actor judged on what they believe about the situation, not actual facts
MPC vs. Common Law
How the MPC approach to use of force for the protection of other persons differs from common law
The most significant difference is the abolition of the common law "alter ego" (or "shoes of the other") rule. Under the older common law approach, a person defending another "stepped into the shoes" of the person defended — if that person was actually the aggressor or otherwise not entitled to use force, the defender had no defense regardless of their honest and reasonable belief. This was widely criticized as unfair because it penalized Good Samaritans who reasonably misread the situation. The MPC and most modern jurisdictions reject the alter ego rule in favor of the subjective belief standard. The MPC treats the defender's reasonable mistake about who is the aggressor the same way it treats reasonable mistakes in self-defense — through the Section 3.09 framework. Many modern common law jurisdictions have now followed the MPC's lead on this point.
Exam Relevance
How § 3.05 appears on criminal law exams
Defense of others questions typically test whether students know the alter ego rule and its MPC rejection. The classic pattern: D sees what appears to be A attacking B, and D uses force against A — but it turns out B was actually the aggressor and A was acting in self-defense. Under the MPC, D is justified if their belief was honest (and if unreasonable, the analysis shifts to Section 3.09). Under the old common law alter ego rule, D would have no defense because B was not entitled to use force. Students should compare approaches and discuss policy rationales — the MPC approach encourages intervention to protect others, while the alter ego rule may deter people from intervening when they are uncertain about the situation.
Related Sections
Sections frequently studied alongside § 3.05
More from Article 3 — General Principles of Justification
Other sections in Article 3