Legal defenses fall into two broad categories: justifications and excuses. Both categories of defenses acknowledge that the criminal act was committed. Justification defenses examine the circumstances existing at the time the act was committed, and excuse defenses examine the defendant’s mental state or beliefs at the time the act was committed. Not every defense fits perfectly within one category or the other and legal scholars sometimes disagree about whether a defense is justified or excused.
Self-Defense and Defense of Others
Justification defenses are those where a defendant claims that the positives of the act outweigh the negatives. If the circumstances are such that the defendant’s conduct, which would otherwise be criminal, is warranted, then the act may be justified. Justification defenses include self-defense, defense of others, necessity and consent.
Self-defense is the use of force towards another person when the actor reasonably believes it is necessary to protect himself against the use of unlawful force by the other person. Tennessee, for example, allows a person to defend herself with as much resistance as necessary to prevent the offense from occurring if the offense (1) is against her person or (2) is an attempt to take or injure property in her possession.
To constitute self-defense, the act must be in response to an immediate threat and accompanied by an act expressing an intent to execute that threat. For example, in a Florida case, a husband threatened to kill his wife from inside their home. He took no action to carry out his threat and his wife shot him from a place of safety outside the home. In this case, self-defense was not established. Similarly, threats of future harm usually cannot serve as the basis for a claim of self-defense.
Still, courts have recognized an exception for systematically abused people who undertake preemptive strikes against their abusers. This defense, colloquially known as “battered women’s syndrome”, can allow a defense or, in some cases, mitigation of the crime when the battered person strikes while the abuser is asleep or during a pause of the abuse.
The force used in self-defense must not exceed the harm threatened. For example, if an actor shoots a would-be-burglar with a machine gun from thirty to forty feet away while the burglar is fleeing and making no aggressive gestures towards the actor, the defense will probably not apply. The law places a greater value on human life than property and deadly force is never justified to prevent a trespass upon property in the absence of an imminent threat against the actor or his family.
One also generally has a duty to retreat before resorting to the use of “deadly force,” which means force likely to cause death or serious injury. An actor must make reasonable efforts to withdraw from a confrontation if he can do so safely. Thus, if one has the ability to walk away from a potentially deadly altercation and chooses not to do so, he will not be able to claim self-defense if he does use deadly force. One exception to the duty to retreat is the castle doctrine. Under the castle doctrine, a person does not have a duty to retreat if attacked in her own home.
For example, in the North Carolina case, State v. Browning, the defendant’s brother advanced towards him with a hammer and a knife in an area of the yard about twenty feet from his back door. The defendant fatally shot his brother. The court held that this area of the yard was close enough to the home so as to entitle the defendant to the benefit of the castle doctrine and to stand his ground.
Many jurisdictions have further limited the duty to retreat if the actor is not engaged in any unlawful behavior and is attacked in any place where he has a right to be. These laws, sometimes known as “stand your ground” laws, have eliminated the duty to retreat when threatened with deadly force, or eliminated it under certain circumstances, such as when the defendant is in his car.
Defense of Others
“Defense of others” is a defense in a criminal proceeding when the defendant uses reasonable force against another person who is threatening to inflict force upon a third party. This defense operates similarly to self-defense in that the threat must be immediate, and the force used must be proportionate. As a general rule, defense of others may only be used when the actor would be justified in using force if he were standing in the shoes of the third party he is defending or when defendant reasonably believes that the third person is in imminent danger of injury, even if the belief is mistaken. The defense may not be used if the offense against the third party has already been completed. For example, if a father learns that his daughter was sexually abused after the fact and he then kills the perpetrator, he cannot claim defense of others because the father did not have a reasonable belief that the daughter was in imminent danger of injury.
The defense of necessity applies when someone commits a criminal act in order to prevent a greater harm from occurring. The defense applies when
(1) the actor reasonably believes the conduct is immediately necessary to avoid imminent harm,
(2) the need to avoid the harm outweighs the harm of defendant violating the law, and
(3) there was no adequate alternative to committing the offense.
For example, if a man drives his pregnant wife to the hospital for medical care while his driver’s license is suspended, the defense of necessity may apply. The defense cannot be used, however, when the defendant creates the situation leading to the necessity of the criminal act (such as by intentionally injuring the person he purports to save). It also cannot be used in cases of intentional homicide, as killing a person is not justified to save a life except in cases of self-defense.
Some crimes, such as rape, require a lack of consent as an element of the crime. Thus, if the victim consents to the act, no crime has actually occurred. The defense can also be used when the actor consents to a criminal act that might otherwise constitute assault. Consent can also be implied by participation in an activity. For example, if someone is injured during a football game the defense will apply because physical injury is a reasonably foreseeable hazard of participation.
The consent must be given intelligently and voluntarily. If someone gives consent while under the influence of drugs and the actor knows the person is unable to exercise a reasonable judgment, the defense of consent will not be available.
For public policy reasons, a person generally cannot consent to violent crimes such as murder or serious assault likely to cause death or serious bodily injury except where the benefit outweighs the risk, as in the case of a life-saving but dangerous surgery.
Excuses: Insanity and Diminished Capacity
Unlike justification defenses, excuse defenses are not asserted to claim that the act was warranted or proper. Excuse defenses are used when the actor’s mental state or belief demonstrate that he should not be held responsible for the criminal act. Excuse defenses include insanity, diminished capacity, duress, mistake, infancy and entrapment.
If a defendant is legally insane at the time he commits the crime, he may be found not guilty by reason of insanity. The legal definition of insanity is not the same as the medical definition of insanity and the existence of a psychological disorder or mental abnormality alone is insufficient to establish that a defendant is legally insane. The insanity defense is not allowed in a few states, but those states do allow a “guilty but insane” verdict that provides for institutionalization instead of a prison sentence. Most states allow a verdict of “not guilty by reason of insanity” (or similar phrasing) that also allow defendants to be institutionalized as criminally insane.
There are four tests that courts around the country use to determine if a defendant is legally insane:
- The M’Naghten Rule, which represents the common law rules, requires that a defendant either (1) not understand what he was doing at the time or (2) not understand that what he was doing was wrong because of a disease of the mind.
- The “Irresistible Impulse” test asks whether or not a defendant was unable to control his impulses which led to the criminal act because of a mental disease.
- The Model Penal Code’s test for insanity requires that a defendant suffer from a mental disease or defect and, as a result, lacks the capacity to appreciate the criminality of his conduct or to conform his conduct to the requirements of the law. The Model Penal Code’s test is mainly a combination of the first two tests in that satisfaction of either test allows the defense to work.
- The Durham Rule states that an accused is not criminally responsible if his unlawful act is a product of mental disease or of mental defect.
Twenty-five states use the M’Naghten Rule and a few of those states also incorporate aspects of the irresistible impulse test into their insanity jurisprudence. Twenty states have adopted the Model Penal Code test. New Hampshire is the only state that uses the Durham Rule. Even within the same jurisdictions, application of the insanity defense can be somewhat inconsistent. Consider the following case examples from New York applying the Model Penal Code test:
In one case, a defendant successfully used the insanity defense after he stabbed a young boy in the chest while playing video games. At the time, the defendant was taking antipsychotic medication and had been diagnosed with paranoid schizophrenia.
In another case, a defendant was unable to succeed with an insanity defense and was convicted of second-degree murder after he pushed a woman onto the subway tracks during a psychotic episode. The defendant suffered from delusions, was schizophrenic, and had been admitted to psychiatric hospitals on numerous occasions in the past.
Diminished capacity is a distinct defense from insanity. A successful insanity defense results in a not guilty verdict, whereas diminished capacity is a defense that often reduces the charge but does not usually absolve the defendant of all responsibility. This defense generally applies only to specific intent crimes, where diminished capacity can negate an element of the crime.
For example, in the California case, People v. Noah, a defendant was involved in an altercation that resulted in a stabbing. He was charged with malicious aggravated assault. Psychiatric evidence was presented to show that the defendant, although sane, suffered from mental defects rendering him incapable of forming the specific intent to assault with malice. The defendant’s diminished capacity defense could be applied to the specific intent crime of malicious aggravated assault but could not be applied to the general intent crime of aggravated assault. The defendant was convicted and sentenced under the lesser charge of aggravated assault.
Duress and Mistake
Duress is a defense to criminal conduct if the person acted while under the threat of imminent serious bodily injury to himself or a third person. Duress is defined as “any unlawful threat or coercion used… to induce another to act in a manner he otherwise would not.” The basis for allowing a duress defense is that the duress experienced would overwhelm the will of an ordinary person. The defense requires proof of four elements: (1) threat of death or serious bodily injury, (2) the threat must be imminent, (3) the threat must create reasonable fear in the actor, and (4) there must be no reasonable means of escape. Implicit threats are sometimes sufficient to raise a duress defense. In the Washington case, State v. Harvill, the defendant was arrested for selling drugs. He testified that he received multiple aggressive phone calls from the purchaser telling him to “get the drugs.” The defendant feared that the purchaser, who had a reputation for violence, would hurt him and his family if he did not provide the drugs. On appeal, the court held that a threat arising indirectly from the circumstances could establish that the defendant acted under duress.
The defense is not available if the defendant recklessly places himself in a situation where he will likely be subject to duress. Like necessity, duress is also not a defense to a charge of homicide.
There are two types of mistake defenses: Mistake of Fact and Mistake of Law. A mistake of fact can negate an element of the crime. For example, if a defendant is charged with theft, but mistakenly believed the property belonged to him, the mistake of fact defense would apply since it negates the specific intent necessary for theft. Mistake of fact is not a defense to crimes in which the mistake was a product of negligence or recklessness.
Ignorance of the law is generally not a defense. That the defendant didn’t know the speed limit or didn’t know that assault was a crime is no defense. For example, in the Texas case, Medrano v. State, the defendant was charged with bigamy. His first wife had deserted him over three years ago and the defendant argued that he was operating under the belief that the marriage had become void due to abandonment. The court ruled that this was a mistake of law and could not be relied upon as a defense.
Still, mistake of law defense can be allowed as a defense when the mistake negates an element of the crime. For example, knowledge that taxes are due is an element of the crime of tax evasion. So, ignorance that one owed taxes can be a defense to a criminal charge of tax evasion.
Other “Excuses” Defenses
The defense of infancy applies when a defendant is below the age of responsibility. Children may be deemed not to have the mental capacity necessary to form criminal intent. The minimum age can vary from jurisdiction to jurisdiction. It is generally accepted that children under the age of seven cannot form criminal intent. Beyond the age of seven, the law provides a presumption that a child below the age of responsibility (16 or 17, typically) was incapable of forming criminal intent. However, the prosecution can rebut the presumption by showing that the child knew what he was doing at the time of the criminal act and that the child knew the act was wrong. Thus, a juvenile defendant may be held criminally responsible even if he is below the age of responsibility. In the Nevada case, Poole v. State, for example, a thirteen-year-old defendant was convicted of second-degree murder. That he was capable of criminal intent was shown in that he hid the murder weapon, fabricated stories to attempt to establish an alibi, claimed the shooting was accidental and testified that he knew killing was wrong.
All states have juvenile justice systems in place to deal with young offenders. In most states, this means defendants under age 17, but some states set the age at 15 or 16. There are significant sentencing differences between juvenile court and criminal court with a much greater emphasis on rehabilitation for juveniles. Juveniles do not have the right to trial by jury.
Underage offenders are sometimes tried and sentenced as adults when the alleged crime is very serious, and/or the juvenile has serious criminal history.
Entrapment occurs when a law enforcement officer induces a person to commit a crime that he would not otherwise have committed for the purpose of instituting a criminal prosecution. It applies in situations when an officer uses deception, persuasion or fraud to convince an actor to engage in unlawful conduct. If police merely provide an opportunity, the defense will not apply. A key inquiry is whether the idea to commit the crime originates with the defendant or with the police.
To succeed with a defense of entrapment, the defendant must also show no predisposition to commit the crime. This inquiry turns on whether the defendant was an “unwary innocent” who had no predisposition or whether the defendant was an “unwary criminal” who readily availed himself of the opportunity police provided. Consider the following case:
The defendant was charged with possessing and selling cocaine and claimed he was entrapped. The Court found that the defendant had a predisposition to commit the crime because he made references to his supplier, cocaine was present in his car and he used drug-trade jargon. That he might not otherwise have completed this particular transaction without undercover police request did not matter.
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 See generally Linda A. Malone, “Is There Really a Difference between Justification and Excuse or Did We Academics Make It Up?” (2009). Faculty Publications. Paper 65.
 Model Penal Code § 3.02.
 Neb. Rev. Stat. Ann. § 28-1409.
 Tenn. Code Ann. § 38-2-102.
 State v. Coles, 91 So. 2d 200, 202-03 (Fla. 1956).
 See generally Lenore E.A. Walker, “Battered Women Syndrome and Self-Defense,” 6 Notre Dame J.L. Ethics & Pub. Pol’y 321 (1992).
 Geralds v. State, 647 N.E.2d 369, 372-73 (Ind. Ct. App. 1995).
 Bullard v. State, 195 N.E.2d 856, 857 (Ind. 1964).
 Redcross v. State, 708 A.2d 1154, 1158-59 (Md. Ct. App. 1998).
 Gainer v. State, 391 A.2d 856, 860-61 (Md. Ct. App. 1978).
 State v. Browning, 221 S.E.2d 375, 377 (N.C. Ct. App. 1976).
 “Self Defense and ‘Stand Your Ground,’” National Conference of State Legislatures, (July 27, 2018), http://www.ncsl.org/research/civil-and-criminal-justice/self-defense-and-stand-your-ground.aspx.
 Idaho Code Ann. § 19-203.
 State v. McNeil, 109 P.3d 1125, 1127-28 (Idaho Ct. App. 2005).
 State v. Arrasmith, 966 P.2d 33, 38 (Idaho Ct. App. 1998).
 Tex. Penal Code Ann. § 9.22.
 State v. Cole, 403 S.E.2d 117, 118-19 (S.C. 1991).
 See KY. REV. STAT. ANN § 503.030.
 See e.g. Del. Code Ann. tit. 11, § 452.
 N.H. Rev. Stat. Ann. § 626:6.
 Durrence v. State, 695 S.E.2d 227, 230 (Ga. 2010).
 Parsons v. State, 81 Ala. 577 at *9, *31 (1887).
 Model Penal Code § 4.01.
 Durham v. United States, 214 F.2d 862, 874-75 (D.C. Cir. 1954), abrogated by US v. Brawner F.2d 969 (D.C. Cir. 1972).
 The Insanity Defense Among the States, FindLaw, https://criminal.findlaw.com/criminal-procedure/the-insanity-defense-among-the-states.html (last visited Nov. 27, 2018).
 Beatrice R. Maidman, “The Legal Insanity Defense: Transforming theLegal Theory into A Medical Standard,” 96 B.U. L. Rev. 1831, 1849-1850 (2016).
 Id. at 1850.
 People v. Noah, 5 Cal. 3d 469, 478 (1971).
 Ind. Code Ann. § 35-41-3-8.
 State v. Harvill, 234 P.3d 1166, 1170 (Wash. 2010).
 18 Pa. Stat. and Cons. Stat. Ann. § 309.
 People v. Anderson, 28 Cal. 4th 767, 50 P.3d 368 (2002).
 Medrano v. State, 22 S.W. 684, 684 (Tex. Ct. Crim. App. 1893).
 “Old Enough to be a Criminal?” Special Protections Progress & Disparity, UNICEF, https://www.unicef.org/pon97/p56a.htm (last visited Nov. 27, 2018).
 Poole v. State, 625 P.2d 1163, 1165 (Nev. 1981).
 Nicole Scialabba, “Should Juveniles Be Charged as Adults in the Criminal Justice System?” American Bar Association (Oct. 3, 2016), https://www.americanbar.org/groups/litigation/committees/childrens-rights/articles/2016/should-juveniles-be-charged-as-adults/.
 Conn. Gen. Stat. Ann. § 53a-15.
 Blanco v. State, 218 So. 3d 939, 943 (Fla. Dist. Ct. App. 2017).
 Sallomi v. State, 629 So. 2d 969, 970 (Fla. Dist. Ct. App. 1993).