Reasonableness Standard

Abstract The reasonableness standard guides many legal judgments about whether to impose criminal liability. Causing harm, such as another's death, through unreasonable or negligent behavior may itself constitute a crime. But reasonableness can be a defense to crime too, as occurs, for example, in self‐defense, where a reasonable belief in the need to use deadly force can sometimes justify a crime.

Reasonableness is sometimes only a partial defense, reducing the potential maximum sentence because a defendant's emotions, while not desirable, were “understandable.” What is “reasonable” may turn on majority views or on normative judgments. The standard is also always one of how the reasonable person would behave “under the circumstances.” What circumstances to count—such as a person's physical infirmities, temperament, race, or gender—is generally a normative question. Juries usually decide reasonableness, though some thinkers see this as a process of masking value judgments as “facts.”