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Definitions Of Probable Cause Vs. Reasonable Suspicion

Definitions Of Probable Cause Vs. Reasonable Suspicion

Probable cause and reasonable suspicion are two of the most important concepts in deciding when it is appropriate for police to make an arrest, search for evidence, and stop a person for questioning. Probable cause and reasonable suspicion have evolved through state and federal court decisions, but they began in the U.S. Supreme Court.

Probable Cause to Arrest  

The Fourth Amendment to the United States Constitution states that people have the right to be free from unreasonable searches and seizures. It goes on to specify that a search warrant cannot be issued unless there is probable cause for doing so. The Constitution does not offer a definition of probable cause. Providing a definition was left to the justices of the Supreme Court.

The Supreme Court has interpreted the Fourth Amendment use of the word “seizure” to mean both the seizure of evidence and, as in an arrest, the seizure of a person. The Court also applied probable cause to:

  • Searches
  • Seizures
  • Arrests conducted without a warrant

According to the Supreme Court, probable cause to make an arrest exists when an officer has knowledge of such facts as would lead a reasonable person to believe that a particular individual is committing, has committed, or is about to commit a criminal act. The officer must be able to articulate the facts and circumstances forming the basis for probable cause.

Probable Cause Vs. Reasonable Suspicion

 Probable Cause to Search and Seize Evidence 

Probable cause to search for evidence or to seize evidence requires that an officer is possessed of sufficient facts and circumstances as would lead a reasonable person to believe that evidence or contraband relating to criminal activity will be found in the location to be searched. As with an arrest, if an officer cannot articulate the facts forming the basis for probable cause, the search and seizure will not hold up in court.

Probable Cause Arrests vs. Arrest Warrants

Reasonable Suspicion 

Reasonable suspicion is a standard established by the Supreme Court in a 1968 case in which it ruled that police officer should be allowed to stop and briefly detain a person if, based upon the officer’s training and experience, there is reason to believe that the individual is engaging in criminal activity. The officer is given the opportunity to freeze the action by stepping in to investigate. Unlike probable cause that uses a reasonable person standard, reasonable suspicion is based upon the standard of a reasonable police officer.


This article contains general legal information but does not constitute professional legal advice for your particular situation. The Law Dictionary is not a law firm, and this page does not create an attorney-client or legal adviser relationship. If you have specific questions, please consult a qualified attorney licensed in your jurisdiction.

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