Definition

The most widely held common definition would be "a reasonable belief that a crime has been committed" and that the person is linked to the crime with the same degree of certainty. An alternative definition has been proposed, "reason to believe that an injury had criminal cause", which is claimed to be more protective of individual rights as was intended by the authors of the Bill of Rights. See the critique below.

In the context of warrants, the Oxford Companion to American Law defines probable cause as "information sufficient to warrant a prudent person's belief that the wanted individual had committed a crime (for an arrest warrant) or that evidence of a crime or contraband would be found in a search (for a search warrant)." "Probable cause" is a stronger standard of evidence than a reasonable suspicion, but weaker than what is required to secure a criminal conviction. Even hearsay can supply probable cause if it is from a reliable source or is supported by other evidence.