Unit 4: Legality Principles


  • Dressler 39-48

  • Mochan (CP)

  • Farinella (CP)

  • Banks (CP)

Key terms: 

  • legality

  • rule of lenity

  • bills of attainder

  • ex post facto laws


One of the core principles of our criminal law system is the legality principle: one cannot be found liable for conduct that is not defined as an offense at the time the conduct occurs. The Constitution provides the basis for the legality principle. Article 1 prohibits legislatures from enacting bills of attainder (special legislation that declares a person guilty without a trial) and ex post facto laws (laws that criminalize conduct after the fact, increase the punishment after the fact, or alter evidence rules to make convictions easier). Through the due process clause of the Fifth and Fourteenth Amendment, the legality principle also applies to the state and federal judiciary, although less strictly than it applies to the legislature. Courts may alter the interpretation of a common law doctrine or statute and apply the new interpretation retroactively, so long as the new interpretation was foreseeable. For example, in Rogers v. Tennessee, 532 U.S. 451 (2001), the Supreme Court held that the Tennessee Supreme Court’s abolition of the common law “year and a day” rule, requiring a murder victim to die within a year and a day of the attack in order for the defendant to be guilty of murder, was not unforeseeable, and therefore could be applied retroactively. The court reasoned that modern medical advances made the purposes underlying the rule non-applicable; most other jurisdictions had abolished the rule, giving notice to the defendant that it might be abolished in Tennessee as well; and the rule had never been applied in Tennessee in an outcome determinative way—the rule was only mentioned in three Tennessee cases total, always in dicta.

Fair Notice

The legality principle dictates that criminal statutes should be understandable and provide fair notice so that people know in advance what conduct is illegal. Statutes do not have to be perfectly clear (that ideal would be unattainable given that statutes have to be broad enough to take into account a wide range of human conduct), but they must be specific enough to avoid criminalizing ordinary conduct. Citizens are responsible for knowing how courts have interpreted certain words in a statute.

Although courts seldom invalidate statutes for vagueness, different types of statutes may require different standards of clarity. To determine if a statute is unconstitutionally vague, courts will consider the purpose of the statute, the necessity of ambiguity in the statute, and the impact of the statute on protected rights. The First Amendment provides some limiting principles to statutes that implicate speech and association, and statutes that have a “chilling effect” on protected speech or association are more likely to be found vague or overbroad.

Principled Delegation

Another corollary of the legality principle is principled delegation: statutes should be crafted so that they do not delegate basic policy matters to police officers, judges and juries for resolution on an ad hoc and subjective basis. Vagrancy statutes such as the one in Morales are sometimes invalidated under this theory.

The Rule of Lenity 

When a statute is subject to two reasonable interpretations, the rule of lenity requires that the statute should be interpreted in a way that favors the defendant.  The lenity principle generally only comes into play as a tiebreaker, and only if the court cannot reasonably ascertain legislative intent. If the court uses all of the tools of statutory interpretation available to it and still finds the statute ambiguous, then the lenity principle requires the court to interpret the statute in favor of the defendant.

The Model Penal Code does not recognize the lenity doctrine.

Questions for Review:

Q1. In In Re Banks, the Supreme Court of North Carolina found that the following statute was not too vague or overbroad: Any person who shall peep secretly into any room occupied by a female person shall be guilty of a misdemeanor and upon conviction shall be fined or imprisoned in the discretion of the court. The court found that the word “secretly” meant that to be guilty under the statute, the offender must have the specific intent to invade a woman’s privacy. Even with this finding, if you were the defense attorney, how would you argue that the statute should be invalidated?

Q2. As a legislator, how would you draft a statute that criminalized Mochan’s conduct but was not overly broad or vague?

Q3. The lenity principle has long been recognized by the common law, but the MPC does not recognize it. Do you think the lenity doctrine should be applied when interpreting statutes? Why or why not?