The Cognitive Psychology of Mens Rea

Abstract

Actus non facit reum nisi mens sit rea - the act does not make a person guilty unless the mind is also guilty. Few today would disagree with the maxim; the criminal law has long since rejected the idea that causing harm should be criminal regardless of the defendant's subjective culpability. Still, the maxim begs a critical question: can jurors accurately determine whether the defendant acted with the requisite guilty mind? Given the centrality of mens rea to criminal responsibility, we would expect legal scholars to have provided a persuasive answer to this question. Unfortunately, nothing could be further from the truth. Most scholars simply presume that jurors can mindread accurately. And those scholars that take mindreading seriously have uniformly adopted common sense functionalism, a theory of mental-state attribution that is inconsistent with a vast amount of research into the cognitive psychology of mindreading. Common-sense functionalism assumes that a juror can accurately determine a defendant's mental state by applying commonsense generalizations about how external circumstances, mental states, and physical behavior are causally related. Research indicates, however, that mindreading is actually a simulation-based, not theory-based, process. When a juror perceives the defendant to be similar to himself, he will mindread through projection, attributing to the defendant the mental state that he would have had in the defendant's situation. And when the juror perceives the defendant to be dissimilar to himself, he will mindread through prototyping, inferring the defendant's mental state from the degree of correspondence between the defendant's act and his pre-existing conception of what the typical crime or defense of that type looks like. This goal of this essay is to provide a comprehensive - though admittedly speculative - explanation of how jurors use projection and prototyping to make mental-state attributions in criminal cases. The first two sections explain why jurors are unlikely to use a functionalist method in a case that focuses on the defendant's mens rea. The next three sections introduce projection and prototyping, describe the evidence that jurors actually use them to make mental-state determinations, and discuss the cognitive mechanism - perceived similarity between juror and defendant - that determines which one a juror will use in a particular case. The final two sections explain why projection and prototyping are likely to result in inaccurate mental-state determinations and discuss debiasing techniques that may make them more accurate.