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Legality, Vagueness and Interpretation
One of the most fundamental defenses to a criminal prosecution is that of nullum crimen sine lege, nulla poena sine lege (“no crime without law, no punishment without law”). In its simplest translation, this Latin maxim asserts the ex post facto prohibition: that conduct must be criminalized and penalties fixed in advance of any criminal prosecution. More broadly, the maxim is also invoked in connection with corollary legislative and interpretive principles compelling criminal statutes to be drafted with precision (the principle of specificity), to be strictly construed without extension by analogy, and to have ambiguities resolved in favor of the accused (the principle of lenity or in dubio pro reo). Together, these precepts undergird the principle of legality and serve several purposes: ensuring that individuals are capable of obtaining notice of prescribed conduct so they can rationally adjust their behavior to avoid sanction; protecting the citizenry from arbitrary or oppressive state action in the face of ambiguities or gaps in the law; and effectuating the expressive purposes of the law by clearly articulating conduct that is collectively condemned. The principle of nullum crimen sine lege writ large thus embodies “an essential element of the rule of law” by speaking to the very legitimacy of a legal rule, providing a check on the power of all branches of government over individuals, and policing the separation of powers by ensuring legislative primacy in substantive rulemaking. Indeed, Alexander Hamilton recognized violations of the principle as “the favorite and most formidable instruments of tyranny.”
Today, most crimes are defined by statutes, which in theory ensures adherence to the legality principle by giving people advance notice of what conduct the law prohibits. Yet some statutes are broadly, ambiguously, or vaguely worded; many statutes require interpretation to understand their meaning in particular contexts and applications. Ordinary people may need to interpret statutes in order to figure out whether their conduct is legal; police and prosecutors must interpret statutes in order to conclude whether they can arrest or charge a person for conduct that they believe violated a statute. Ultimately, courts' interpretation of criminal statutes are definitive, and for this reason case law--in addition to a statute's text--continues to be an important source the understanding the precise meaning of criminal law. As cases in this chapter illustrate, the Constitution is understood to prohibit excessively "vague" statutes, so courts occasionally hold that statutes are "void for vagueness." But more often, courts use a variety of tools--sometimes called 'canons' of interpretation or construction--to interpret statutes whose meanings are in some respect unclear or uncertain, without invalidating them as excessively vague. As the case, Nash, illustrates, statutes can be quite vague by any ordinary standard and yet not deemed to be unconstitutionally vague.
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