Under the tradition of common law, judges would often require a "bad state of mind" in addition to an action or omission (
actus reus) to find a criminal guilty. Over time, culpable mental states (
mens rea) became varied among different types of crimes. Within the United States, there is no single encompassing criminal law. Criminal laws are passed and enforced by the states‚ or the federal government, but each of these criminal "codes" vary and may or may not draw from the same theoretical sources.
State criminal law The vast majority of criminal prosecutions in the United States are carried out by the
several states in accordance with the laws of the state in question. Historically, the states (with the partial exception of
civil-law Louisiana) applied common law rules of
mens rea similar to those extant in England, but over time American understandings of common law
mens rea terms diverged from those of English law and from each other. Concepts like "general intent" and "specific intent" dominated classifications of mental states in state common law, but by the late 1950s to early 1960s, the common law of
mens rea was widely acknowledged to be a slippery, vague, and confused mess. This was one of several factors that led to the development of the Model Penal Code. Nevertheless, states continue to use mental states beyond or besides those listed in the Model Penal Code. Supreme Court Justice
Stephen Breyer described the distinction between the two systems in his dissent in
Delling v. Idaho:
Federal criminal law Since the federal government of the United States does not have a generalized
police power like that of the states, the scope of its criminal statutes is necessarily circumscribed. Ordinary prosecutions are the province of the states, and only crimes connected to the constitutional powers may be pursued by the federal government. Nevertheless, the Supreme Court holds that required
mens rea is an essential element of federal criminal offenses. Consequently, Title 18 of the
United States Code does not use the aforementioned culpability scheme but relies instead on more traditional definitions of crimes taken from common law. For example,
malice aforethought is used as a requirement for committing capital murder, and the Supreme Court has applied mental states such as "willfully."
Model Penal Code Because the landscape of criminal law varied from state to state, the
American Law Institute (which issues "restatements" of American legal jurisprudence) declined to issue a restatement of criminal law in favor of a "model" code for states to issue new, standardized criminal law. This
Model Penal Code ("MPC") was completed in 1962, and received praise from legal scholars for its reformulation of criminal law. Although not all states follow the criminal law as constructed within the MPC, over 34 states had adopted part or substantially all of the MPC as law by 1983. •
Negligently: a "reasonable person" ought to be aware of a "substantial and unjustifiable risk" that is a "gross deviation" from a normal standard of care. •
Recklessly: the actor "consciously disregards a substantial and unjustifiable risk" in "gross deviation" from a normal standard of care. or is aware to a high probability that his conduct is of a prohibited nature, or is aware to a high probability that the attendant circumstances exist. •
Purposefully: the actor
consciously engages in conduct and "desires" the result. The Supreme Court has not found a large difference between purposeful and knowing conduct, not only in theory but also in application. The MPC also recognizes culpability not because of a mental state, but for crimes that are legislatively proscribed due to the imposition of "absolute liability." Strict liability crimes will require evidence of such legislative intent, and courts seriously examine such evidence before assuming a crime permits strict liability rather than a mens rea. •
Strict liability: the actor engaged in conduct and his mental state is irrelevant. This
mens rea may only be applied where the forbidden conduct is a mere violation, i.e. a
civil infraction.
Differences between common law crimes and MPC crimes The elements constituting a crime vary between codes that draw on common law principles and those that draw from the Model Penal Code. For example, the
mens rea required of murder in federal law under the
United States Code is distinct from the
mens rea of murder under the
Texas Penal Code (which adopted the Model Penal Code in 1974 Many states still adhere to older terminology, relying on the terms "intentional" to cover both types of
mens rea: "purposeful" and "knowing".
Limits and criticisms of MPC mens rea Not all states have adopted the MPC, and for states that have, application of the Model Code varies. Despite its attempt to standardize criminal law, this variance has resulted in confusion and criticism. Some scholars have criticized the levels of culpability in the current Model Penal Code as insufficient or needing revision. Scholars' allegations include incoherency from conflicted philosophical commitments, or the federal governments' failure to explicitly adopt the Model Penal Code resulting in departure from common law precedents. Since the publication of the MPC, confusion has also occurred where norms towards crimes have also changed: especially regarding sexual crimes, hate crimes, drug crimes, and digital crimes. But while some scholarship argues that commitment to reforms gave way to "cynicism and fatigue," Rather than dwell on philosophical or normative arguments, some scholars have looked to evidence-based arguments to update the Code. In an empirical study, participants were presented with scenarios and asked to rate how deserving of punishment the scenario was. The results showed that participants' judgments matched up with the hierarchy of
mens rea in the MPC, but also found that participants struggled most with "recklessness" scenarios. As a result, the study suggests revising the language of the categories. == Modes of culpability outside the United States ==