What is Criminal Law?

You don’t need a law degree to answer this question, but here goes:  The term “criminal law” is generally defined as body of rules and statutes that defines conduct prohibited by the government because it threatens and harms public safety and welfare.

In addition to defining and prohibiting such conduct, criminal statutes describe the punishments to be imposed for engaging in criminal activity.  Although there are some common law crimes, most crimes in the United States are established by local, state, and federal governments. Criminal laws vary significantly from state to state.

There is, however, a Model Penal Code (MPC) which serves as a good starting place to gain an understanding of the basic structure of criminal liability.  Acts defined as crimes include both felonies (serious offenses such as murder and armed robbery) and misdemeanors (less serious offenses, such as shoplifting or jaywalking).

The Model Penal Code

The Essential Guide to Criminal Law

Felonies are usually punishable by imprisonment of a year or more, while misdemeanors are generally punishable by less than a year.  Most criminal laws subdivide felonies into different classes with varying degrees of punishment.

The Elements of a Crime

All statutes describing criminal behavior can be broken down into their various elements. Most crimes consist of two elements: an act, or “actus reus,” and a mental state, or “mens rea“. Prosecutors have to prove each and every element of the crime to yield a conviction.

Furthermore, the prosecutor must persuade the jury or judge “beyond a reasonable doubt” of every fact necessary to constitute the crime charged. In civil cases, the plaintiff needs to show a defendant is liable only by a “preponderance of the evidence,” or more than 50%.

The Act

All crimes must involve an act that is undertaken by the defendant.  The act requirement is fulfilled when the defendant purposely, knowingly, or recklessly does something prohibited by law. An act is purposeful when a person holds a conscious objective to engage in certain conduct or to cause a particular result. To act knowingly means to do so voluntarily and deliberately, and not owing to mistake or some other innocent reason. An act is reckless when a person knows of an unjustifiable risk and consciously disregards it.

An omission, or failure to act, may constitute a criminal act if there is a duty to act. For example, a parent has a duty to protect his or her child from harm. A parent’s failure to take reasonable steps to protect a child could result in criminal charges if the omission were considered to be at least reckless.

Ordinarily, a person cannot be convicted of a crime unless he or she is aware of all the facts that make his or her conduct criminal. However, if a person fails to be aware of a substantial and unjustifiable risk, an act or omission involving that risk may constitute negligent conduct that leads to criminal charges, if  the defendant took a very unreasonable risk by acting or failing to act.


To successfully convict someone of a crime, a prosecutor must also prove that the defendant intended to commit the crime he or she is accused of, and that intent must be formed before, and result in, the act.   The intent need not have been formed at any particular length of time before the act.  They can can take place within a split second of each other. If intent is not clear from direct evidence, a jury may infer a defendant’s intent to commit the act  from facts that would lead a reasonable person to believe that it existed.  For example, the intent to commit murder may be inferred if the defendant is found to have had a gun in his possession prior to the murder taking place.

Criminal intent may also be presumed from the commission of the act, if the act has natural and probable consequences that anyone would be aware of.  For example, the intent to commit vandalism may be demonstrated by the particular act that caused the vandalism, i.e., the defendant’s throwing a rock at a window.  The defendant may rebut this presumption by introducing evidence showing a lack of criminal intent.  For example, if the vandalism defendant intended to harmlessly toss the rock but suffered from a muscle spasm that cause it to be thrown at the window.

Proof of general criminal intent is required for the conviction of most crimes. The intent element is usually fulfilled if the defendant was generally aware that he or she was very likely committing a crime. This means that the prosecution need not prove that the defendant was aware of all of the elements constituting the crime. For example, in a prosecution for the possession of more than a certain amount of a controlled substance, it is not necessary to prove that the defendant knew the precise quantity. Other examples of general-intent crimes are Battery, rape,Kidnapping, and False Imprisonment.

Some crimes require a specific intent, which the prosecution must prove as an independent fact.  For example, to show intent to commit robbery, the prosecutor must present evidence showing that the defendant specifically intended to steal the property.  The main difference between specific and general intent is that with general intent crimes, intent may be inferred from the commission of the act, while the opposite is true with specific intent.  Examples of specific-intent crimes are solicitation, attempt, conspiracy, first-degree premeditated murder, assault, Larceny, robbery, burglary, forgery, false pretense, and Embezzlement.

Most criminal laws require that the specified crime be committed with knowledge of the act’s criminality and with criminal intent. However, some statutes make an act criminal regardless of intent. When a statute is silent as to intent, knowledge of criminality and criminal intent need not be proved. Such statutes are called Strict Liability laws. Examples are laws forbidding the sale of alcohol to minors, and Statutory Rape laws.