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Concept: Actus reus


A coherent practice of mens rea (‘guilty mind’) ascription in criminal law presupposes a concept of mens rea which is insensitive to the moral valence of an action’s outcome. For instance, an assessment of whether an agent harmed another person intentionally should be unaffected by the severity of harm done. Ascriptions of intentionality made by laypeople, however, are subject to a strong outcome bias. As demonstrated by the Knobe effect, a knowingly incurred negative side effect is standardly judged intentional, whereas a positive side effect is not. We report the first empirical investigation into intentionality ascriptions made by professional judges, which finds (i) that professionals are sensitive to the moral valence of outcome type, and (ii) that the worse the outcome, the higher the propensity to ascribe intentionality. The data shows the intentionality ascriptions of professional judges to be inconsistent with the concept of mens rea supposedly at the foundation of criminal law.

Concepts: Intentionality, Concepts in metaphysics, Thought, Criminal law, Intention, Motive, Mens rea, Actus reus


In American criminal law, actus non facit reum, nisi mens sit rea, “an act does not make one guilty, without a guilty mind.” Both actus reus and mens rea are required to justify criminal liability. The Model Penal Code’s (MPC) section on culpability has been especially influential on mens rea analysis. An issue of increasing importance in this realm arises when an offensive act is committed while the actor is under the influence of drugs. Several legal doctrines address the effect of intoxication on mental state, including the MPC, limiting or eliminating its relevance to the mens rea analysis. Yet these doctrines do not differentiate between intoxication and addiction. Neuroscience research reveals that drug addiction results in catastrophic damage to the brain resulting in cognitive and behavioral deficits. Methamphetamine addiction is of particular interest to criminal law because it causes extensive neural destruction and is associated with impulsive behavior, violent crime, and psychosis. Furthermore, research has revealed important distinctions between the effects of acute intoxication and addiction. These findings have implications for the broader doctrine of mens rea and, specifically, the intoxication doctrines. This Note argues for the adoption of an addiction doctrine that acknowledges the effect of addiction on mens rea that is distinct from doctrines of intoxication.

Concepts: Psychology, Brain, Drug addiction, Heroin, Crime, Criminal law, Mens rea, Actus reus