Introduction

Mental States for Criminal Liability

Introduction

A driver passes a school during the morning hours when students arrive, travelling 30 m.p.h. over the speed limit, and strikes and kills a child who is trying to cross the road. He stops at once, jumps out, and protests when confronted that he never meant to kill anyone and is not a bad person.¹ Most people would still call him guilty of a homicide, though they would blame him less than a calculating killer who stalks a victim for days before running the victim down.² The harm is the same in both cases, a dead child, so the difference in blame cannot come from the result. It comes from the defendant's mind: what he wanted, what he was aware of, and what he should have noticed. The part of criminal law that sorts defendants this way is mens rea, Latin for “guilty mind,” and it limits liability to blameworthy defendants by requiring some mental connection to each act, fact, or result that makes up the crime.³ The demand for a culpable mind is old. In Morissette v. United States the Supreme Court described the view that an injury is a crime only when inflicted by intention as universal and persistent in mature legal systems, and it observed that courts have protected defendants who were not blameworthy in mind through labels such as “malice aforethought,” “guilty knowledge,” and “mens rea.”⁴

The Model Penal Code turns that intuition into a rule. Under Model Penal Code § 2.02(a), a person is not guilty of an offense unless he acted purposely, knowingly, recklessly, or negligently, “as the law may require,” with respect to “each material element of the offense,” subject to an exception in § 2.05 that this chapter leaves aside.⁵ Each quoted phrase does separate work. The words “as the law may require” mean that the definition of the offense determines which of the four levels the prosecutor must prove. The words “each material element” mean that the mental connection is measured against the individual building blocks of the offense, so culpability becomes a question asked about every element in turn. Culpability, the blameworthiness these four levels measure, therefore has to be shown element by element, except in cases of absolute liability.⁶ The reason is practical: a careful driver and a deliberate killer can cause the same death, and a law that looked only at the death would punish them alike and would have no vocabulary for ranking one defendant's blame against another's.

The label mens rea is itself shorthand. For some crimes the required fault is only recklessness or negligence, which are not true states of mind, and a few strict-liability crimes require no culpable mental state at all. The vocabulary also differs by legal tradition. English common law produced many mental-state terms, such as wilfully, maliciously, and intentionally, with no necessary relationship to one another, whereas the Code recognizes four precisely defined levels that stand in a logical relationship and mean the same thing wherever they appear.⁷ This chapter follows that contrast. The first half builds the Code's framework: the element-by-element requirement, the four culpability levels, the way a higher level can stand in for a lower one, and the rules that fill gaps when an offense definition is silent or unclear about mental state. The second half turns to common-law murder, whose mental element is the term of art malice aforethought, and closes by showing how the two vocabularies map onto each other. The place to begin is the phrase in § 2.02(a) that carries the most weight: what does it mean to require a mental state “with respect to each material element” of an offense?⁸