The Sources and Limitations of the Criminal Law

Principle of Legality

Today, most jurisdictions have enacted comprehensive modern criminal statutes and have abolished courts’ authority to create new crimes. This clear preference for a statutory criminal law reflects a collective sense of justice that individuals are entitled to the protection afforded by clearly announced rules that both protect individual autonomy and limit governmental authority. Fair warning is an essential part of the American criminal justice system. Relying on statutes rather than cases to create crimes also supports separation of powers: the legislature makes the law; courts interpret and apply the law.

The principle of legality is an important part of American criminal law today, a principle expressed in the often-cited Latin maxim: “Nullum crimen, nulla poena, sine lege “ (“There is no crime without law, no punishment without law”). Today, a defendant cannot be convicted of a crime unless the legislature has enacted in advance a statutory definition of the offense.[8]

Providing prior notice of illegality by statute also supports the reasons for convicting and punishing lawbreakers. Utilitarians would concede that, before deterrence can be effective, an individual must be able to know what conduct is forbidden and the consequences of breaking the law. Most retributivists conclude that the fundamental purpose of punishment is to blame those who choose to do wrong. Unless adequate notice of criminal behavior is provided, it is difficult to argue that the defendant has “chosen” to commit a wrongful act. Moral condemnation and punishment without such notice are indefensible.

Ex Post Facto

The Constitution expressly forbids both Congress and state legislatures from passing ex post facto criminal laws.[9] Legislatures cannot enact statutes that criminalize acts that were innocent when done or that increase the severity of the crime or the punishment after the fact. Such laws are a form of retroactive criminalization. This constitutional restraint ensures that the legislature give fair warning of criminal conduct and its consequences.[10]

The ex post facto prohibition is expressly limited to legislatures. Nonetheless, American courts today are sensitive to the basic unfairness created by unforeseen judicial interpretations of criminal statutes that expand their reach and, in effect, retroactively criminalize behavior or aggravate the severity of the crime or its punishment. Concern that due process prohibits such judicial construction of criminal statutes and respect for the separation of powers have influenced courts to avoid such interpretations.[11]