• The U.S. legal system defines probable cause as evidence or facts that would make a reasonable person believe a crime or wrongdoing has been, is being or will be committed. Probable cause is only based on facts and evidence, and not just suspicion.

    Four Sources

    Probable cause must be established by four sources. These sources are observation, expertise, information and circumstantial evidence.

    The Fourth Amendment

    The Fourth Amendment is the constitutional clause that limits the police force from unlawfully searching, seizing and arresting individuals. This amendment is the basis for courts in determining the proper use of probable cause.

    Search Warrants

    Without the proper determination of probable cause in a given situation, no person shall have their property or persons searched or violated. Warrants can be issued when there is probable cause and they must be supported by oath or affirmation that describes places to be searched or person or things to be seized.


    The police can detain and hold a person in a public place if they have reasonable cause for doing so. This is why officers sometimes stop and frisk people without probable cause. Without probable cause, an arrest cannot be made.


    Law enforcement personnel must be extremely careful and not violate a citizen's rights. Without the Fourth Amendment and the rulings that derive from it, law enforcement could have unchecked power when it comes to arresting, detaining and searching individuals whether they're guilty or not.



    U.S. Legal Definitions

    Austin Peay State University

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