Introduction

Acts, Omissions, and Voluntariness

Introduction

Criminal liability rests on conduct. Bad thoughts alone cannot constitute a crime, and liability requires either an act or an omission to act where the law imposes a duty to act.¹ The same idea underlies the rule that status crimes are unconstitutional, because people may be punished only for their conduct and never simply for being a certain kind of person.² In the usual account, this conduct requirement is the actus reus, the guilty-act element, which sits beside the mens rea, or mental-state element, in most offenses.³ Conduct alone is still not enough if the bodily movement behind it was never the person's own choice, and the difference shows most clearly when two cases end the same way.

The Code treats the first driver's steering as a voluntary act and the second driver's convulsion as something outside that category, because a reflex or convulsion is expressly listed as involuntary.⁴ That result comes from Model Penal Code § 2.01, the provision that organizes this topic.⁵ Subsection (1) states the voluntary act requirement as the general rule: a person is not guilty of an offense unless liability rests on conduct that includes a voluntary act, or the omission to perform an act of which the person is physically capable.⁶ The rule has two halves because a person can cause harm by doing something or by failing to do something, and each route carries its own threshold: voluntariness for an act, and physical capacity for an omission, since no one can fairly be blamed for failing to do what the person could not physically do. Subsection (2) lists the movements that are not voluntary acts, and subsection (3) allows an omission to support liability only where the law defining the offense makes it sufficient or a duty to perform the omitted act is otherwise imposed by law.⁷ Subsection (4) treats possession as an act when the possessor knowingly procured or received the thing possessed, or was aware of control over it long enough to have ended the possession.⁸

Three definitions from the Code's general provisions frame how § 2.01 does its work. Section 1.13 defines an act as a bodily movement, whether voluntary or involuntary, defines an omission as a failure to act, and defines conduct as an action or omission together with its accompanying state of mind or, where relevant, a series of acts and omissions.⁹ Because the definition of act is this broad, the word covers a spasm as readily as a deliberate step, and the same section sends the word voluntary back to § 2.01 for its meaning.¹⁰ The screening therefore happens in § 2.01, which separates the bodily movements that can ground liability from those that cannot. Although conduct as defined includes the actor's state of mind, the physical side of conduct, the act or omission itself, corresponds roughly to the actus reus, and that physical side is what this chapter takes up.¹¹ The chapter moves from the voluntary-act rule to the movements the Code excludes, then to omissions and the legal duties that make them punishable, and finally to possession. The first task is to state the baseline rule and the line it draws between a movement the person willed and one the person did not, which is where the next section begins.