§ 5.01 Principle of Legality
[A] “Legality”: Definition
There are a lot of things in this world that you shouldn’t do, but not all of them are crimes. In our legal system, only things that are defined by statute as criminal can be punished. This is the overarching doctrine of the American legal system, and it even supercedes the interest in punishing guilty defendants.
1. Regular people should be able to understand criminal statutes.
2. Criminal statutes should be clear enough such that major policy decisions are not left to the executive or judicial branches of government.
3. When courts interpret statutes, they should lean in favor of the defendant.
The principle of legality prevents the government from abusing its enemies using the criminal justice system. It maximizes personal freedom by minimizing the risk that someone can break a law without being aware of it. The legality principle also assures “fair warning” of what conduct is considered criminal and what punishments may be enforced against such conduct. “Fair warning” is important for both retributive and utilitarian justifications of the criminal justice system.
The latter argument may be seen as weak because people rarely look at penal codes before deciding how to act, and if they do, it’s so they can be as bad as possible without getting punished.
Courts rarely invalidate a law for being too vague. However, retroactive laws are not enforced.
[C] Constitutional Law
 Bill of Attainder and Ex Post Facto Clauses
The Constitution forbids laws that declare the guilt and punishment of a specific person. It also forbids the retroactive application of laws.
 Due Process Clause
The due processes clauses in the Fifth and Fourteenth amendments are the judicial analogue of the ex post facto and bill of attainder prohibitions.
§ 5.02 Statutory Clarity
Vague statutes are unconstitutional because they fail to give people fair warning as to what conduct is unlawful.
Courts look at several criteria to determine whether statutes are too vague. In particular, courts will find statutes unconstitutional if they could be construed to impair an important constitutional right, such as free speech.
Barring such constitutional problems, judges rarely find criminal statutes to be too vague. For example, it is permissible for a statute to hold people to an imprecise standard of good behavior.
The ideal behind statutory clarity is far from the reality. Most people neither have the time, training, or else money to actually research criminal statutes before they act.
§ 5.03 Avoiding Undue Discretion in Law Enforcement
Vague statutes allow cops and prosecutors to discriminate against people.
Several examples of “loitering” ordinances that have been found unconstitutional are provided.
§ 5.04 Strict Construction of Statutes (Rule of Lenity)
If a statute is unclear, the court needs to consider what the intent of the legislature was in drafting the statute.
The rule of lenity says that when there’s a tie between the state and the accused, the accused wins. It only kicks in when there’s really a tie and the court is right on the razor’s edge with its decision.
Since statutes can be interpreted different ways, lenity may cause courts to act contrary to legislative intent. For this reason, many states and the Model Penal Code have rejected the Rule of Lenity.