The eighth amendment`s prohibition of cruel and unusual punishment prohibits punishment that is grossly disproportionate to criminality. The Supreme Court ruled that a sentence of 15 years of hard labour was a constitutionally prohibited sanction for a public official who had falsified a minor document. Similarly, the death sentence of a convicted rapist has been classified as cruel and unusual punishment. Ex post facto laws are laws that aim to retroactively make previously legal conduct illegal, retroactively increase a penalty, retroactively change the rules of evidence in a criminal case, or retroactively change the definition of a crime. Ex post facto laws are prohibited by the Constitution. The authors believed that it was imperative to give citizens an idea of the behavior that could be punished and that it was important to prevent the tyranny of those in power. Criminal laws must also be comprehensible to persons with ordinary information. If a reasonable person cannot determine what a law is trying to order or prohibit, that law will be struck down as void because of its vagueness. The doctrine of vagueness derives from the clauses of the Fifth and Fourteenth Amendments. Laws prohibiting vagrancy have sometimes been attacked as void because a language does not contain an adequate warning about the type of behavior that might violate the law.