The criminal law needs a practical and consistent method to describe the behavior for which its special power of arrest, conviction, and punishment may be used. Simply put, it needs a basic architecture to define crime. Although they may differ on their reasons, most utilitarians and retributivists agree on the basic elements of a crime.
Voluntary Act. Subject to some exceptions we will discuss shortly, the criminal law only punishes voluntary action; it does not punish inaction or mere thinking. The “voluntary act” element of a crime is usually called the actus reus.