03 Criminal Law and Criminal Liability
Learn how U.S. criminal law defines offenses, establishes criminal liability, recognizes defenses, and limits punishment.
What governs
defines conduct the government may punish and sets rules for deciding whether a person is legally responsible. A criminal prosecution is brought by the government for a public offense, unlike a civil lawsuit, which usually resolves a dispute between private parties. differs across states and between state and federal systems, so the applicable statute and jurisdiction matter.
Sources of
In the United States, comes chiefly from constitutions and statutes. State legislatures define most crimes, while Congress defines federal crimes, many of which appear in Title 18 of the U.S. Code. A statute typically identifies prohibited conduct and sets available penalties. The federal government generally may prosecute only offenses within its constitutional authority.
Courts interpret statutes and constitutional rules, and their decisions create precedent. Some states also retain or incorporate parts of common-law criminal doctrine, although legislatures have defined many offenses by statute.
Legality and fair notice
Criminal laws must give people fair notice of what is prohibited. The government may not retroactively make previously lawful conduct criminal or increase punishment for past conduct. These requirements are part of legality: criminal liability must rest on a law that existed when the conduct occurred.
Elements of an offense
The prosecution generally must prove every element of the charged offense . The governing law supplies the exact elements. Depending on the offense, those elements may include conduct, a mental state, attendant circumstances, and a result with a required causal connection.
The conduct element, or , is usually a voluntary act. In limited circumstances, it may be a failure to act when the person had a legal duty to do so. A reflexive movement ordinarily is not a voluntary act.
Attendant circumstances are facts that must exist for the conduct to be criminal. For example, an offense may require that property belong to another person. If an offense requires a particular result, such as injury or death, the prosecution must establish the required causal connection between the defendant’s conduct and that result.
Mental states and
The mental-state element, or , is the culpability required by the offense. A widely used framework distinguishes acting purposely, knowingly, recklessly, or negligently. The statute determines which mental state applies and to which elements.
Some regulatory or other narrowly defined offenses impose for one or more elements, so the prosecution need not prove a culpable mental state for those elements. Whether an offense is depends on the statute and its interpretation. should not be assumed merely because a law is silent about intent.
Applying the elements
Consider a theft statute that requires taking another person’s property with the purpose of keeping it. The prosecution must establish the taking, that the property belonged to someone else, and the required purpose. Accidentally carrying away a similar-looking bag may raise a question about intent; believing the bag was one’s own may prevent proof of an essential element.
Defenses to criminal liability
A defendant may argue that the prosecution has failed to prove an element. If the factfinder has a reasonable doubt about any required element, the defendant must be acquitted. A defense may negate an offense element, establish a or , or bar prosecution for a procedural or constitutional reason. The burden of proof for particular defenses can differ, but the prosecution retains the burden to prove the crime’s elements .
A claims the conduct was legally permissible in the circumstances. Self-defense, for example, may justify reasonable force used against an imminent unlawful threat, subject to jurisdiction-specific rules.
An accepts that the conduct was wrongful but argues that the defendant should not be held fully responsible under the circumstances. Duress is one example; its availability and requirements vary, and it is not a defense to every offense.
Other defenses and jurisdictional variation
Other defenses may contest identity, raise a legally recognized mistake, or challenge whether the defendant had the capacity or required mental state. Insanity is a distinct legal defense whose test differs among jurisdictions; it is not simply a medical diagnosis. Defenses and their requirements vary by jurisdiction and offense.
Purposes of punishment
Punishment is commonly justified by several aims. means proportionate accountability for wrongdoing; seeks to discourage the defendant or others from offending; reduces opportunities for further crime; and supports changes that may reduce future offending. Some systems also emphasize repairing harm to victims and communities.
These purposes can conflict. For example, a severe sentence may incapacitate someone while doing little to rehabilitate them.
Statutory and constitutional limits
Federal law directs sentencing courts to impose a sentence “sufficient, but not greater than necessary” to serve statutory purposes. It identifies just punishment, , public protection, and treatment or training among the considerations. This is a federal sentencing framework; state laws differ.
Punishment is also constitutionally limited. The Eighth Amendment prohibits cruel and unusual punishments, and constitutional doctrine restricts certain punishments that are grossly disproportionate or based on a person’s status rather than prohibited conduct. Due process requires fair procedures, including proof of each element. Punishment is therefore not unlimited merely because a legislature has prohibited conduct.