§ 9.01 Actus Reus: General Principles

§ 9.01 Actus Reus: General Principles¹

[A] Definition

Generally speaking, crimes have two components: the "actus reus," the physical or external portion of the crime; and the "mens rea," the mental or internal feature.² The concept of "actus reus" is the focus of this chapter.

The term "actus reus" was not generally used by scholars in criminal law treatises prior to the twentieth century,³ but it has found currency in modern Anglo-American jurisprudence. Unfortunately, there is no single accepted definition.

As used in this text, the term "actus reus" generally includes three ingredients of a crime, which can be encapsulated in a single sentence: The actus reus of an offense consists of (1) a voluntary act (or, rarely, a failure to act⁴); (2) that causes; (3) social harm.⁵ For example, if A picks up a knife and stabs B, killing B, the actus reus of a criminal homicide has occurred: A has performed a voluntary act (stabbing B) that caused B's death (the social harm). As is developed in this chapter, "voluntary act" and "social harm" are legal terms of art that require special attention. The element of causation, which links the defendant's voluntary act to the social harm, is discussed in Chapter 14.⁶

[B] Punishing Thoughts: Why Not?

Suppose that three people separately would like the President of the United States to die: A fantasizes killing the President; B, intending to kill the President, devises a mental plan to commit the offense, but goes no further; and C actually kills the President. A society might plausibly punish all three persons. A would be punished for her morally objectionable fantasy; B would be punished for mentally devising her wrongful plan; and C would be punished for acting out her intentions. In Anglo-American criminal law, however, only C is punishable, as "[t]he reach of the criminal law has long been limited by the principle that no one is punishable for his thoughts."⁷

Reasons of pragmatism and principle justify the non-criminalization of mere thoughts. On a pragmatic level, the requirement of conduct is "[r]ooted in skepticism about the ability . . . to know what passes through the minds of men."⁸ We often have difficulty accurately reconstructing our own thoughts, much less "reading" another person's mind! Science fiction authors, however, have envisioned a world in which scientists — and, therefore, the government — will be able to read our thoughts.⁹ What if such science fiction becomes science reality? Even now, scientists are able to use electrodes to measure brain waves and, with some...