Model Penal Code
The Model Penal Code is a statutory text which was developed by the American Law Institute
American Law Institute
The American Law Institute was established in 1923 to promote the clarification and simplification of American common law and its adaptation to changing social needs. The ALI drafts, approves, and publishes Restatements of the Law, Principles of the Law, model codes, and other proposals for law...

 (ALI) in 1962. The Chief Reporter on the project was Herbert Wechsler
Herbert Wechsler
Herbert Wechsler was a legal scholar and former director of the American Law Institute . He is most widely known for his constitutional law scholarship and for the creation of the Model Penal Code...

. The current form of the MPC was last updated in 1981. The purpose of the MPC was to stimulate and assist legislatures in making an effort to update and standardize the penal law
Penal law
In the most general sense, penal is the body of laws that are enforced by the State in its own name and impose penalties for their violation, as opposed to civil law that seeks to redress private wrongs...

 of the United States of America. Primary responsibility for criminal law lies with the individual states, and such national efforts work to produce similar laws in different jurisdictions. The standard they used to make a determination of what the penal code should be was one of "contemporary reasoned judgment" — meaning what a reasoned person at the time of the development of the MPC would judge the penal law to do. The ALI performed an examination of the penal system in the USA and the prohibitions, sanctions, excuses, and authority that are used throughout. The MPC was a combination of what the ALI deemed to be the best rules for the penal system in the United States. Since its formulation, the MPC has played an important role in standardizing the codified penal laws of the United States.

Element Analysis

Under the MPC, crimes are defined in terms of a set of "elements of the offense," each of which must be proven to the finder of fact beyond a reasonable doubt. There are three types of elements:
  1. conduct of a certain nature,
  2. attendant circumstances at the time of the conduct, or
  3. the result of that conduct.

The elements are those facts that:
  1. are included in the definition of forbidden conduct as provided by the statute, or
  2. establish the required culpability, or
  3. negate an excuse or justification for such conduct, or
  4. negate a defense under the statute of limitation, or
  5. establish jurisdiction or venue.

All but the last two categories are material elements, and the prosecution must prove that the defendant had the required kind of culpability with respect to that element.

Mens rea or Culpability

One of the major innovations of the MPC is its use of standardized mens rea
Mens rea
Mens rea is Latin for "guilty mind". In criminal law, it is viewed as one of the necessary elements of a crime. The standard common law test of criminal liability is usually expressed in the Latin phrase, actus non facit reum nisi mens sit rea, which means "the act does not make a person guilty...

 terms (criminal mind, or in MPC terms, culpability) to determine levels of mental states, just as homicide is considered more severe if done intentionally rather than accidentally. These terms are (in descending order) "purposely", "knowingly," "recklessly", and "negligently
Criminal negligence
In the criminal law, criminal negligence is one of the three general classes of mens rea element required to constitute a conventional as opposed to strict liability offense. It is defined as an act that is:-Concept:...

", with a fifth state of "strict liability
Strict liability (criminal)
In criminal law, strict liability is liability for which mens rea does not have to be proven in relation to one or more elements comprising the actus reus although intention, recklessness or knowledge may be required in relation to other elements of the offence...

". Each material element of every crime has an associated culpability state that the prosecution must prove beyond a reasonable doubt.
  • Purposely. If the element involves the nature of the conduct or the result thereof, it is his conscious object to engage in that conduct or cause the result. If the element involves attendant circumstances, he is aware of the circumstances or believes or hopes that they exist.
  • Knowingly. If the element involves the nature of the conduct or the attendant circumstances, he is aware that his conduct of that nature or that the circumstances exist. If the element involves a result, he is practically certain that the result will occur. Further, if the element involves knowledge of the existence of a particular fact, it is satisfied if he is aware of a high probability of the existence of that fact, unless he actually believes that it does not exist.
  • Recklessly. A person consciously disregards a substantial and unjustifiable risk that the element exists or will result, such that its disregard involves a gross deviation from the standard of conduct that a law-abiding person would observe.
  • Negligently. A person should be aware of a substantial and unjustifiable risk that the element exists or will result, such that the failure to perceive it involves a gross deviation from the standard of conduct that a reasonable person would observe.

If an offense requires a specific kind of culpability, then any more severe culpability will suffice. Thus if an offense is defined in the form, "It is illegal to knowingly do X," then it is illegal to do X knowingly or purposely (a more severe state), but not to do so recklessly or negligently (the two less severe states). Strict liability means that it is illegal to do something, regardless of one's mental state. If a statute provides only a single kind of culpability for a crime, that kind of culpability is assumed to apply to all elements. If no culpability is stated by statute, a minimum of recklessness is assumed to be required. The MPC declines to use the common terms "intentional" or "willful" in its specification of crimes, in part because of the complex interpretive history of these terms. However, it defines that any (non-MPC) statute in the jurisdiction's criminal code that uses the term "intentionally" shall mean "purposely," and any use of "willfully" shall mean "with knowledge." If a law makes an actor absolutely liable for an offense, the actor can only be guilty of what the MPC calls violations, which only deserve penalties of fines, and no jail time. See sections 2.05 and 1.04.

Unlawful acts explicitly set forth

Another important feature is that under the MPC, any action not explicitly outlawed is legal. This concept follows the saying, "That which is not forbidden is allowed" as opposed to "That which is not allowed is forbidden." Legal scholars contrast the MPC's limits with laws passed by Nazi Germany
Nazi Germany
Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...

 and the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

, which allowed people to be punished for acts not specifically outlawed but similar to acts that were. The MPC provision has a prospective effect in that it applies to those acts which may be committed in the future. This is not the same as a retrospective effect of past acts which are protected by the rule against ex post facto laws.

Under the MPC, ignorance of criminal law
Ignorantia juris non excusat
Ignorantia juris non excusat or ignorantia legis neminem excusat is a legal principle holding that a person who is unaware of a law may not escape liability for violating that law merely because he or she was unaware of its content...

 is not considered a valid defense, unless the legislature intended on making the mistake of law
Mistake of law
Mistake of law is a legal principle referring to one or more errors that were made by a person in understanding how the applicable law applied to their past activity that is under analysis by a court. In jurisdictions that use the term, it is typically differentiated from mistake of fact...

 a defense, the law is unknown to the actor and had not been published, or the actor is acting as a result of some official statement about the law. See sections 2.02(9) and 2.04.

Options for enacting jurisdictions

Certain parts of the MPC contain multiple options, inviting states
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

 to choose one. A particularly controversial topic is the proper place of the death penalty in the MPC. However, the MPC explicitly states that the "[American Law] Institute took no position on the desirability of the death penalty." Note that no state is obligated to adopt any specific part of the MPC; see below.


Advocates of the MPC stress that the law must be clearly defined to prevent arbitrary enforcement, or a chilling effect on a population that does not know what actions are punishable. This is known as the legality principle. However, critics say that the assumption that there are no possible legal systems between the extremes of "forbidden" and "allowed" is the central weakness of the MPC. British law, for example, assumes that a jury can decide what is "reasonable" both in the context of British law and social expectations as well as the specific accusation they are being asked to judge. Behavior may thus be deemed unlawful by a jury in cases where the MPC would require legislative change to produce a conviction.


The MPC is not law in any jurisdiction
Jurisdiction is the practical authority granted to a formally constituted legal body or to a political leader to deal with and make pronouncements on legal matters and, by implication, to administer justice within a defined area of responsibility...

 of the United States; however, it served and continues to serve as a basis for the replacement of existing criminal codes in over two-thirds of the states. Many states adopted portions of the MPC, but only states such as New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...

, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

, Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...

, and Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

 have enacted almost all of the provisions. Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

 adopted the model penal code in its entirety in 1971, but the legislature repealed this action in 1972.

The repeal of the MPC in Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

 came about after intense rejection of the new codification due to the lack of laws regulating morality
Morality is the differentiation among intentions, decisions, and actions between those that are good and bad . A moral code is a system of morality and a moral is any one practice or teaching within a moral code...

, problems with the MPC in certain areas that affected important political groups in the state, and also prosecutors
The prosecutor is the chief legal representative of the prosecution in countries with either the common law adversarial system, or the civil law inquisitorial system...

 and police
The police is a personification of the state designated to put in practice the enforced law, protect property and reduce civil disorder in civilian matters. Their powers include the legitimized use of force...

 who were critical of some areas of the new MPC-based code. The state bar association
State bar association
A state bar association is a bar association that represents or seeks to represent all of the attorneys in a specific U.S. state. Membership in such an association may be voluntary or mandatory for practitioners in that state. State bar associations may be tasked with the administration of the...

, judiciary committees in the legislature, and the Supreme Court of Idaho defended the new code based on the MPC. Chief in the objections were the omission of sodomy
Sodomy is an anal or other copulation-like act, especially between male persons or between a man and animal, and one who practices sodomy is a "sodomite"...

, adultery
Adultery is sexual infidelity to one's spouse, and is a form of extramarital sex. It originally referred only to sex between a woman who was married and a person other than her spouse. Even in cases of separation from one's spouse, an extramarital affair is still considered adultery.Adultery is...

 and fornication
Fornication typically refers to consensual sexual intercourse between two people not married to each other. For many people, the term carries a moral or religious association, but the significance of sexual acts to which the term is applied varies between religions, societies and cultures. The...

 as crimes, as well as objection by gun owners of the new stricter gun control law
Gun politics in the United States
Gun politics in the United States refers to an ongoing political and social debate regarding both the restriction and availability of firearms within the United States. It has long been among the most controversial and intractable issues in American politics...


On rare occasions, the courts will turn to the MPC for its commentary on the law and use it to seek guidance in interpreting non-code criminal statutes. It is also used frequently as a tool for comparison.

Section 230.3 Abortion (Tentative draft 1959, Official draft 1962) of the MPC was used as a model for abortion law
Abortion in the United States
Abortion in the United States has been legal in every state since the United States Supreme Court decision in Roe v. Wade, on January 22, 1973...

 reform legislation enacted in 13 states from 1967 to 1972. It is included as Appendix B of Justice Blackmun
Harry Blackmun
Harold Andrew Blackmun was an Associate Justice of the Supreme Court of the United States from 1970 until 1994. He is best known as the author of Roe v. Wade.- Early years and professional career :...

's opinion in the January 22, 1973 Doe v. Bolton
Doe v. Bolton
Doe v. Bolton, 410 U.S. 179 , was a landmark decision of the United States Supreme Court overturning the abortion law of Georgia. The Supreme Court's decision was released on January 22, 1973, the same day as the decision in the better-known case of Roe v. Wade, 410 U.S...

 decision of the United States Supreme Court
Supreme Court of the United States
The Supreme Court of the United States is the highest court in the United States. It has ultimate appellate jurisdiction over all state and federal courts, and original jurisdiction over a small range of cases...

 (Roe v. Wade
Roe v. Wade
Roe v. Wade, , was a controversial landmark decision by the United States Supreme Court on the issue of abortion. The Court decided that a right to privacy under the due process clause in the Fourteenth Amendment to the United States Constitution extends to a woman's decision to have an abortion,...

s lesser-known companion case).

In October 2009, the ALI voted to disavow the framework for capital punishment
Capital punishment
Capital punishment, the death penalty, or execution is the sentence of death upon a person by the state as a punishment for an offence. Crimes that can result in a death penalty are known as capital crimes or capital offences. The term capital originates from the Latin capitalis, literally...

that it had included in the MPC, "in light of the current intractable institutional and structural obstacles to ensuring a minimally adequate system for administering capital punishment." A study commissioned by the institute had said that experience had proved that the goal of individualized decisions about who should be executed and the goal of systemic fairness for minorities and others could not be reconciled.
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