Criminal Defenses: An Overview

Criminal Defenses: An Overview

Criminal law defines prohibited conduct and establishes when a person may be held criminally responsible. But criminal law also recognizes that not every person who appears to have committed a prohibited act should necessarily be convicted.

A person may have acted in self-defense.

A person may have been forced to act by an immediate threat.

A person may have acted to prevent a greater harm.

A person may have been legally insane.

A person may have made a mistake that prevented the required mental state from existing.

Or the prosecution may simply be unable to prove one of the elements of the offense beyond a reasonable doubt.

These situations are addressed through criminal defenses.

A criminal defense is a legal or factual basis that prevents, limits, or defeats criminal liability. Cornell’s Legal Information Institute describes defenses broadly as grounds through which a defendant may prevent or limit liability, including factual and legal grounds. Cornell Legal Information Institute — Defense

The important point is that not all defenses operate in the same way.

Some defenses say:

“The prosecution has not proved that I committed the crime.”

Others say:

“I committed the prohibited act, but the law considers my conduct justified.”

Still others say:

“I committed the act, but circumstances make me less or not at all blameworthy.”

Understanding these distinctions is essential to understanding criminal responsibility.

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1. What Is a Criminal Defense?

A criminal defense is a legal basis on which a defendant seeks to avoid or limit criminal liability.

Cornell’s LII identifies several broad categories, including failure of proof, mistakes, justifications, and excuses. Cornell Legal Information Institute — Criminal Law

A defense may challenge:

• an element of the offense;
• the defendant’s mental state;
• the voluntariness of the conduct;
• the circumstances surrounding the conduct;
• the legality of the government’s conduct;
• the admissibility of evidence; or
• the defendant’s legal responsibility despite proof of the underlying conduct.

The word defense therefore covers a very broad range of legal arguments.

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2. The First and Simplest Defense: Failure of Proof

The prosecution has the burden of proving the elements of a criminal offense.

If the prosecution fails to prove even one required element beyond a reasonable doubt, the defendant should be acquitted.

This is not necessarily an “affirmative defense.”

It is simply a demand that the prosecution satisfy its burden.

For example, suppose a defendant is charged with a crime requiring intentional conduct.

The prosecution proves that the defendant performed the physical act but cannot prove the required intent.

The defendant can argue:

The prosecution has failed to prove an element of the offense.

No additional justification may be necessary.

This distinction is fundamental.

A defendant does not ordinarily have to prove innocence.

The prosecution must prove guilt.

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3. Defenses That Attack an Element of the Crime

Some defenses operate by showing that an element of the offense does not exist.

For example, a prosecution may require:

• a voluntary act;
• a particular mental state;
• causation;
• possession;
• knowledge;
• intent;
• a particular circumstance; or
• a prohibited result.

If the defendant can establish a reasonable doubt concerning the required element, the prosecution may fail.

Consider a possession offense.

If the prosecution cannot establish that the defendant knowingly possessed the prohibited item, the possession element may not be satisfied.

Or consider a specific-intent offense.

If the evidence creates reasonable doubt about the defendant’s required intent, the prosecution may fail even though the physical act occurred.

These are sometimes called failure-of-proof defenses because they challenge the prosecution’s proof rather than introducing a separate justification.

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4. Affirmative Defenses

An affirmative defense operates differently.

Cornell’s LII defines an affirmative defense as a defense in which the defendant introduces evidence that, if found credible, can negate criminal liability even when the defendant committed the alleged acts. Cornell Legal Information Institute — Affirmative Defense

Examples can include:

• self-defense;
• insanity;
• necessity;
• duress; and
• entrapment.

The exact classification and burden of proof can vary by jurisdiction and by defense.

This is important because the phrase affirmative defense does not mean that the defendant generally carries the burden of proving innocence.

Rather, certain defenses require the defendant to raise and, under applicable law, establish particular facts.

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5. Justification Defenses

A justification defense argues that the conduct itself was legally justified under the circumstances.

Cornell’s LII describes justification as a defense based on the idea that the defendant’s conduct was justified or not wrongful under the circumstances. Cornell Legal Information Institute — Justification

The classic example is self-defense.

Imagine that someone unlawfully attacks another person.

The person being attacked uses reasonable force to stop the attack.

The physical conduct may otherwise resemble assault.

But if the requirements of self-defense are satisfied, the law treats the conduct as justified.

The important conceptual point is:

The defendant is not merely excused from wrongdoing. The circumstances make the conduct legally permissible.

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6. Self-Defense

Self-defense is one of the most familiar criminal defenses.

It generally concerns the use of force to protect oneself from unlawful force or threatened injury.

Cornell Legal Information Institute — Self-Defense

Although the exact rules vary by jurisdiction, questions commonly include:

• Was the defendant confronted with unlawful force?
• Was the threat imminent?
• Did the defendant reasonably believe force was necessary?
• Was the force used proportionate to the threat?
• Was the defendant the initial aggressor?
• Did the defendant have a duty to retreat under applicable law?

For example:

A person is attacked with a knife and uses reasonable force to stop the attacker.

The law may regard the response as justified.

But:

A person is insulted and responds by using deadly force.

Self-defense is far less likely to apply because the nature and proportionality of the threat are fundamentally different.

Self-defense will be examined in much greater detail in a later article.

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7. Defense of Others

The law may also recognize the right to use reasonable force to protect another person from unlawful harm.

This is commonly known as defense of others.

For example:

A person sees an attacker violently assaulting another individual and intervenes with reasonable force to stop the attack.

The precise requirements vary by jurisdiction.

The underlying principle resembles self-defense:

The law may justify otherwise criminal conduct when the conduct is reasonably necessary to prevent unlawful harm to another person.

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8. Defense of Property

Some jurisdictions also recognize a defense involving the use of force to protect property.

The rules are generally more restrictive than those governing defense of human life or physical safety.

The law distinguishes between:

• protection of property;
• prevention of theft;
• prevention of trespass;
• protection against violent intrusion; and
• use of deadly force.

The precise rules vary significantly by jurisdiction.

The important conceptual point is that the law may recognize circumstances in which conduct that would otherwise constitute a crime is legally justified because it protects a recognized interest.

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9. Necessity

The necessity defense is sometimes described as the “choice of evils” defense.

It generally applies when a person commits an otherwise unlawful act to prevent a more serious harm.

Cornell’s LII describes necessity as a defense where unlawful conduct is justified because it prevents a greater threatened harm and the actor has no reasonable alternative. Cornell Legal Information Institute — Necessity Defense

For example:

A person breaks into an unoccupied building during a severe emergency to obtain shelter from an immediate threat to life.

The question is not simply whether the person technically violated a criminal statute.

The question is whether the circumstances made the violation legally justified.

Typical questions include:

• Was there an imminent threat?
• Was the threatened harm sufficiently serious?
• Was there a reasonable alternative?
• Was the defendant’s response proportionate?
• Did the defendant create the emergency?
• Did the defendant actually and reasonably believe the conduct was necessary?

The exact requirements vary by jurisdiction.

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10. Excuse Defenses

Justification and excuse are conceptually different.

A justification defense says:

“The conduct was right or permissible under the circumstances.”

An excuse defense says:

“The conduct was wrongful, but this defendant should not be held fully responsible for it.”

This distinction is fundamental to criminal-law theory.

Consider two situations.

Justification

A person uses force to stop an imminent unlawful attack.

The law may say:

The conduct was justified.

Excuse

A person commits a criminal act because another person threatens immediate death unless the act is performed.

The conduct may remain wrongful, but the defendant argues that the coercive circumstances excuse the conduct.

This distinction helps explain why criminal defenses are not all based on the same theory.

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11. Duress

Duress generally involves criminal conduct committed because another person uses unlawful threats or coercive pressure.

Cornell’s LII describes criminal duress as an affirmative defense based on conduct compelled by a sufficiently serious threat, with the precise requirements varying by jurisdiction. Cornell Legal Information Institute — Duress

For example:

A criminal organization threatens to kill a person unless the person transports an illegal package.

The defendant may argue that the threat destroyed meaningful freedom of choice.

Duress typically focuses on threats from another person.

That distinguishes it conceptually from necessity, which more often involves circumstances or forces not caused by another person’s coercion.

The distinction is not absolute in every jurisdiction.

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12. Insanity

The insanity defense concerns a defendant’s mental condition at the time of the offense.

It asks whether a legally recognized mental disease or defect prevented the defendant from possessing the required degree of criminal responsibility.

Cornell’s LII explains that insanity is a legal defense based on mental illness or defect and that jurisdictions use different tests, including the M’Naghten rule and the Model Penal Code approach. Cornell Legal Information Institute — Criminal Insanity

A successful insanity defense may result in a verdict such as not guilty by reason of insanity, rather than an ordinary acquittal followed by unrestricted release.

The exact consequences vary by jurisdiction.

Insanity should also be distinguished from competence to stand trial.

These are different questions:

Insanity: Was the defendant legally responsible at the time of the offense?

Competency: Is the defendant currently capable of understanding and participating in the criminal proceedings?

Those concepts should never be treated as interchangeable.

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13. Diminished Capacity

Diminished capacity is related to insanity but is not the same doctrine.

A diminished-capacity argument generally focuses on whether a mental condition prevented the defendant from forming a particular mental state required for an offense.

Cornell’s LII distinguishes diminished capacity from insanity, noting that diminished capacity can operate to negate an element such as intent rather than necessarily providing a complete excuse. Cornell Legal Information Institute — Insanity and Diminished Capacity

For example:

A defendant is charged with a crime requiring specific intent and argues that a legally recognized mental impairment prevented formation of that intent.

The result may be:

• acquittal of the charged offense;
• conviction of a lesser offense; or
• no effect, depending on the jurisdiction and offense.

This is one reason the distinction between failure of proof and affirmative excuse is important.

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14. Mistake of Fact

A mistake of fact occurs when a person has an incorrect understanding of the circumstances.

Whether it is a defense depends upon:

• the offense;
• the required mental state;
• whether the mistake was reasonable;
• whether the mistake was honest;
• and the applicable jurisdictional rules.

For example:

A person takes an umbrella believing it belongs to them, when in fact it belongs to someone else.

If theft requires a particular mental state concerning ownership or intent to deprive, the mistake may be relevant.

The mistake does not automatically excuse the conduct.

Instead, the question is:

Does the mistake prevent the prosecution from proving the mental state required by the offense?

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15. Mistake of Law

A mistake of law occurs when a person misunderstands the legal status of conduct.

The general principle is much less forgiving than mistake of fact.

A person ordinarily cannot escape criminal responsibility simply by saying:

“I did not know that this conduct was illegal.”

This principle is associated with the general idea that ignorance of the law is not ordinarily a defense.

But there are important exceptions and qualifications.

For example, the exact wording of a statute may require knowledge of a particular legal fact or status.

The Supreme Court has also recognized circumstances in which a person’s misunderstanding of law can matter when the statute itself makes knowledge of the law relevant to an element.

Mistake-of-law doctrines therefore require careful analysis rather than an absolute rule.

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16. Voluntary and Involuntary Conduct

A criminal offense generally requires legally relevant conduct.

An involuntary movement may not satisfy the actus reus requirement.

For example:

A person has an involuntary seizure and strikes another individual.

The physical movement occurred.

But if it was genuinely involuntary, criminal liability may fail because the required voluntary act was absent.

This is fundamentally a failure-of-proof issue rather than a traditional affirmative defense.

The law therefore distinguishes between:

• voluntary conduct;
• reflexive movements;
• unconscious movements;
• seizures;
• sleep-related conduct; and
• other forms of involuntary behavior.

The principle connects directly with the criminal-law requirement of actus reus.

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17. Intoxication

Intoxication may sometimes affect criminal liability.

But the rules differ depending upon whether intoxication was:

• voluntary; or
• involuntary.

Voluntary intoxication generally has limited use as a defense.

In some jurisdictions, however, it may be relevant to whether the defendant formed a particular specific intent.

Involuntary intoxication may have broader consequences.

The precise rules depend heavily upon jurisdiction and offense.

Intoxication therefore should not be treated as a universal defense to criminal conduct.

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18. Entrapment

Entrapment concerns government involvement in criminal conduct.

A defendant may claim that law enforcement induced the defendant to commit a crime that the defendant otherwise would not have committed.

Cornell’s LII describes entrapment as an affirmative defense involving inducement by law enforcement or a state agent. Cornell Legal Information Institute — Entrapment

Under the traditional subjective approach used in many jurisdictions, the defense generally focuses on:

1. government inducement; and
2. lack of predisposition to commit the crime.

The Supreme Court addressed the issue in Jacobson v. United States, emphasizing that government inducement must be distinguished from simply providing an opportunity to commit a crime.

Cornell Legal Information Institute — Jacobson v. United States

Entrapment therefore does not mean:

“The police gave me an opportunity.”

It concerns whether government conduct improperly induced criminal conduct that otherwise would not have occurred.

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19. Consent

Consent is highly dependent upon the particular offense.

In some criminal cases, consent may have little or no legal significance.

In others, the absence of valid consent is itself part of the offense.

Cornell’s LII notes that consent is generally not a defense to criminal charges, although it may be relevant to offenses such as rape and sexual assault and in other contexts where consent is legally significant. Cornell Legal Information Institute — Consent

The key question is therefore:

Does the criminal statute make the absence of consent an element of the offense, or otherwise recognize consent as a defense?

Consent must not be treated as a universal criminal defense.

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20. Constitutional and Procedural Defenses

Not every criminal defense concerns whether the defendant’s conduct was justified or excused.

Some defenses challenge the government’s conduct or the legal process itself.

Examples may involve:

• unconstitutional searches;
• unlawful seizures;
• violations of due process;
• improper interrogation;
• violations of the right to counsel;
• unconstitutional discrimination;
• speedy-trial violations;
• double jeopardy; and
• suppression of illegally obtained evidence.

These issues belong partly to criminal procedure rather than substantive criminal law.

They can nevertheless have decisive consequences for a criminal prosecution.

For example, if critical evidence is suppressed because it was obtained unlawfully, the prosecution may become unable to prove its case.

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21. Failure of Proof vs. Affirmative Defense

This is one of the most important distinctions in the subject.

Failure of proof

The defendant says:

“The prosecution has not proved an element of the crime.”

Example:

“The prosecution cannot prove that I knowingly possessed the item.”

Affirmative defense

The defendant says:

“Even if the prosecution has proved the basic offense, additional circumstances make me legally justified or excused.”

Example:

“I used force, but I did so in lawful self-defense.”

The distinction matters because the burden of proof may operate differently.

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22. Justification vs. Excuse

Another essential distinction is between justification and excuse.

Justification

The conduct is considered permissible under the circumstances.

Examples include:

• self-defense;
• defense of others;
• certain forms of defense of property;
• necessity.

Excuse

The conduct remains wrongful, but the defendant’s responsibility is reduced or eliminated because of circumstances affecting blameworthiness.

Examples may include:

• duress;
• insanity;
• certain forms of involuntary intoxication.

The distinction is primarily theoretical, but it helps explain why different defenses are structured differently.

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23. Complete and Partial Defenses

Some defenses completely defeat criminal liability for the offense.

Cornell’s LII describes a complete defense as one that, when established, eliminates liability for the claim at issue. Cornell Legal Information Institute — Complete Defense

Other defenses may have only a partial effect.

For example, a particular defense may:

• negate a specific-intent element;
• reduce a charge;
• establish a lesser offense;
• mitigate punishment; or
• affect sentencing without producing acquittal.

The precise effect depends on the jurisdiction and the defense involved.

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24. The Burden of Proof and Criminal Defenses

The burden of proof is especially important in criminal defenses.

The prosecution generally bears the burden of proving the elements of the offense beyond a reasonable doubt.

But the burden associated with an affirmative defense may vary.

Some jurisdictions require the defendant merely to produce evidence supporting the defense.

Others may place a burden of persuasion on the defendant.

Constitutional limitations also matter.

The allocation of burdens must therefore be analyzed carefully rather than assuming one universal rule.

Cornell’s LII provides an overview of the concept of affirmative defenses and notes that the burden may rest on the party raising the defense, although the precise rule depends on the applicable law. Cornell Legal Information Institute — Affirmative Defense

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25. The Defendant Does Not Always Have to Prove Innocence

This point is worth emphasizing.

Suppose the prosecution charges a defendant with murder.

The defendant argues:

“The prosecution has not established that I was the person who committed the killing.”

That is not an affirmative defense.

The defendant is challenging the prosecution’s evidence.

The prosecution must prove guilt.

Similarly, if the prosecution cannot prove the required mens rea, the defendant may be entitled to acquittal without proving an alternative explanation.

This reflects one of the foundational principles of criminal law:

The government bears the burden of proving criminal guilt.

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26. Multiple Defenses Can Be Raised

A defendant may rely on more than one defense.

For example, a defendant might argue:

1. the prosecution cannot prove the required intent;
2. alternatively, the defendant acted in self-defense;
3. alternatively, the force used was justified under another applicable doctrine.

The availability of multiple defenses does not necessarily mean that they are factually or legally consistent.

Criminal defense strategy may involve presenting alternative theories because the defendant does not know which factual proposition the jury will accept.

The important principle is that defenses can operate at different levels.

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27. Defenses Depend on the Specific Crime

There is no universal list of defenses that applies identically to every crime.

The relevance of a defense depends upon the elements of the offense.

For example:

• self-defense is particularly relevant to crimes involving force;
• mistake of fact may be relevant where a crime requires knowledge or intent;
• insanity may affect criminal responsibility;
• necessity may apply to certain emergency conduct;
• entrapment concerns government inducement;
• consent may matter where lack of consent is part of the offense.

A defense should therefore never be analyzed in isolation.

The first question should always be:

What exactly must the prosecution prove?

Only then can the relevance of a particular defense be evaluated.

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28. A Practical Framework for Analyzing Criminal Defenses

When analyzing a criminal defense, use the following sequence.

Step 1: Identify the offense

What crime has been charged?

Step 2: Identify every element

What must the prosecution prove?

Step 3: Examine the prosecution’s evidence

Has every element been established?

Step 4: Look for failure of proof

Could the prosecution fail because an element is missing?

Step 5: Identify the proposed defense

Is it:

• failure of proof?
• justification?
• excuse?
• affirmative defense?
• mistake?
• constitutional or procedural defense?

Step 6: Determine the legal requirements

What must be established for the defense to apply?

Step 7: Analyze the burden

Who must produce evidence?

Who bears the burden of persuasion?

What standard applies?

Step 8: Examine the facts

Do the actual circumstances satisfy the defense?

Step 9: Consider alternative defenses

Could another defense apply if the first fails?

Step 10: Determine the effect

Would the defense produce:

• acquittal;
• failure to prove an element;
• a lesser offense;
• suppression of evidence;
• mitigation; or
• another legal consequence?

This framework prevents the common mistake of treating every defense as simply:

“I did it, but I had a reason.”

Criminal defenses are much more sophisticated than that.

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29. Common Misunderstandings

“A defense means the defendant admits committing the crime.”

Not necessarily.

A defendant may simply argue that the prosecution has failed to prove an element.

“The defendant always has to prove the defense.”

Not necessarily.

The burden varies by defense and jurisdiction.

“Self-defense means any force is lawful if the defendant felt threatened.”

Incorrect.

Requirements such as reasonableness, imminence, necessity, proportionality, and aggressor status may apply.

“Insanity means the defendant was mentally ill.”

Not automatically.

Legal insanity is a specific legal standard, not simply a medical diagnosis.

“Necessity and duress are the same.”

They overlap, but necessity generally involves circumstances creating the emergency, while duress ordinarily involves coercion by another person.

“Entrapment means the police gave the defendant an opportunity.”

Incorrect.

Entrapment generally requires improper inducement and, under the subjective approach, lack of predisposition.

“Ignorance of the law is always a defense.”

Generally no.

Mistake of law is ordinarily much more restricted than mistake of fact.

“Every defense results in acquittal.”

Not necessarily.

Some defenses may negate a particular element, reduce liability, affect the offense of conviction, suppress evidence, or influence sentencing.

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30. The Deeper Principle: Criminal Defenses Define the Boundaries of Responsibility

Criminal law is not simply a list of prohibited acts.

It is a system for determining when a person should be held responsible for prohibited conduct.

That requires two complementary questions.

First:

What conduct does the law prohibit?

Second:

When should a person be held responsible for engaging in that conduct?

Criminal defenses help answer the second question.

A person may perform an act that appears criminal but nevertheless lack the required mental state.

A person may perform an act intentionally but under circumstances that justify it.

A person may perform a wrongful act but under coercive circumstances that excuse the conduct.

A person may be unable to understand the nature or wrongfulness of the conduct because of legally recognized insanity.

Or the government may simply fail to prove its case.

The defense system therefore places limits on the reach of criminal punishment.

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31. Criminal Defenses and Moral Responsibility

The law of criminal defenses also reflects a deeper philosophical question:

When is a person blameworthy?

Imagine two people who perform exactly the same physical act.

Person A deliberately attacks an innocent victim for personal gain.

Person B uses force to stop an imminent attack on another person.

The physical conduct may look similar.

The moral and legal circumstances are entirely different.

Likewise, compare:

• a person who commits a crime freely;
• a person forced to act under an immediate threat of death;
• a person who acts under a legally recognized mental incapacity; and
• a person whose conduct was genuinely necessary to prevent a greater harm.

Criminal law distinguishes among these situations because punishment is not supposed to depend solely on physical causation.

It depends upon culpability.

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32. Criminal Defenses and the Presumption of Innocence

The law of defenses also fits within the larger structure of the presumption of innocence.

A defendant begins the criminal process without a presumption of guilt.

The prosecution must establish the elements of the offense.

Only after the prosecution’s case is understood can the role of a particular defense be properly analyzed.

This is why the distinction between:

“The prosecution failed to prove the crime”

and

“The defendant committed the act but has a legal defense”

is so important.

The first concerns the government’s proof.

The second concerns an additional legal principle affecting responsibility.

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33. Criminal Defenses Are Jurisdiction-Specific

Although criminal law has broad common-law traditions, the exact rules governing defenses vary considerably across U.S. jurisdictions.

Differences may concern:

• available defenses;
• definitions;
• burdens of proof;
• evidentiary requirements;
• retreat rules;
• insanity tests;
• intoxication;
• necessity;
• duress;
• mistake;
• consent;
• entrapment; and
• sentencing consequences.

Even when two jurisdictions recognize the same defense, they may formulate its elements differently.

For that reason, general criminal-law principles should always be distinguished from the law of the particular jurisdiction.

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Key Takeaways

• A criminal defense is a legal or factual basis for avoiding or limiting criminal liability.
• Not every defense is an affirmative defense.
• Failure of proof argues that the prosecution has not established an element of the offense.
• Justification argues that the conduct was legally permissible under the circumstances.
• Excuse argues that the conduct was wrongful but the defendant should not be held fully responsible.
• Common justification defenses include self-defense, defense of others, defense of property, and necessity.
• Common excuse defenses include duress and insanity.
• Mistake of fact may sometimes negate a required mental state.
• Mistake of law is generally much more restricted.
• Involuntary conduct may defeat the actus reus requirement.
• Intoxication can sometimes affect criminal responsibility, but its availability varies significantly.
• Entrapment concerns improper government inducement.
• Consent is highly dependent on the specific offense.
• Constitutional and procedural doctrines can also provide powerful defenses or grounds for excluding evidence.
• The burden of proof for affirmative defenses varies by jurisdiction and defense.
• The first step in analyzing any defense is to identify exactly what the prosecution must prove.
• Criminal defenses ultimately define the boundaries of criminal responsibility and culpability.

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Frequently Asked Questions

What is a criminal defense?

A criminal defense is a legal or factual argument that prevents, limits, or defeats criminal liability.

Does a defense mean that the defendant admits committing the crime?

No. A defendant may argue that the prosecution has failed to prove an element of the offense without admitting guilt.

What is an affirmative defense?

An affirmative defense is a defense that can negate criminal liability even when the underlying conduct has been established. Examples include self-defense, insanity, necessity, duress, and entrapment, although classification and burdens vary by jurisdiction. Cornell Legal Information Institute — Affirmative Defense

What is a justification defense?

A justification defense argues that the defendant’s conduct was legally permissible under the circumstances. Self-defense is the classic example.

What is an excuse defense?

An excuse defense accepts that the conduct was wrongful but argues that circumstances make the defendant insufficiently blameworthy to justify criminal punishment.

What is the difference between justification and excuse?

Justification says:

The conduct was permissible.

Excuse says:

The conduct was wrongful, but the defendant should not be held fully responsible.

Is self-defense an affirmative defense?

It can be, depending on the jurisdiction. The exact burden and procedural treatment vary among jurisdictions.

Is insanity the same as mental illness?

No. A medical diagnosis does not automatically satisfy the legal requirements for insanity. Criminal insanity is determined according to the applicable legal test. Cornell Legal Information Institute — Criminal Insanity

Is necessity the same as duress?

No. They are closely related but conceptually distinct. Necessity generally involves circumstances or forces creating a choice between harms, while duress generally involves coercion by another person. Cornell Legal Information Institute — Necessity Defense

Can a defendant raise more than one defense?

Yes, where permitted by applicable law. Defendants may present alternative defenses or theories concerning the prosecution’s failure of proof.

Does every defense result in an acquittal?

No. Some defenses negate an element, produce a lesser offense, suppress evidence, or otherwise affect criminal liability or punishment.

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Conclusion

Criminal defenses are not exceptions tacked onto criminal law after the fact.

They are part of the architecture of criminal responsibility itself.

Criminal law establishes what conduct is prohibited, but defenses establish when punishment is nevertheless inappropriate.

The distinction between failure of proof, justification, and excuse provides the foundation for understanding the subject.

A failure-of-proof defense says that the prosecution has not established the crime.

A justification defense says that the conduct was legally permissible under the circumstances.

An excuse defense says that the conduct was wrongful but that the defendant’s circumstances make criminal responsibility inappropriate.

Other defenses address mistakes, involuntary conduct, intoxication, government misconduct, constitutional violations, and other circumstances that can prevent or limit liability.

The central lesson is therefore:

Criminal liability requires more than proof that a prohibited act occurred. The law must also determine whether the defendant possessed the required culpability and whether any recognized defense makes criminal punishment inappropriate.

That is why criminal defenses are fundamental to the structure of criminal law.

They mark the boundary between conduct that the law condemns and conduct for which the law may legitimately impose punishment.