One of the great complaints about the civil law system is that you can sue over anything. Although this is not strictly true, the civil law system is designed to be very flexible and to provide remedies for new problems that have not yet been anticipated by the courts or the legislatures. The administrative law system also has very broad authority to deal with new problems, or to apply new solutions to old problems, much to the chagrin of a regulated industry, as anyone who tries to keep up with Medicare/Medicaid rules can attest. In contrast, the common law tradition and the Constitution require that a person be given specific notice of what constitutes a crime. For example, the Constitution bans ex post facto laws— those that are passed to criminalize behavior that has already occurred—and bills of attainder— laws passed to punish specific individuals without trial or other due process protections. [Fletcher v. Peck, 6 Cranch 87 (1810).]

More generally, a defendant may attack a criminal law as vague or overbroad, meaning that it does not define the crime or the elements of the crime in such a way that a reasonable person would know what was illegal. If the court agrees, it will declare the law unconstitutional, preventing the prosecution of the defendant. As a result of this constitutional requirement, criminal statutes are very specific, spelling out the required details of the crime. This is most true when the crime is a conventional crime against another person, such as rape, murder, assault, or fraud. The standards for business- related crimes, such as antitrust or Medicare fraud, are much less specific, sometimes saying little more than that submitting a false claim is a crime. Although such laws have been attacked for vagueness and overbreadth, these challenges have been unsuccessful.