Probable cause

Probable cause is a reasonable basis, grounded in specific facts, to believe that a crime occurred or that a person committed one. It is a legal threshold for searches, arrests, and some warrants.

Arrest: An arrest is the restraint of a person by legal authority to answer for an alleged offense. Probable cause generally supplies the constitutional basis for a warrantless arrest.
Reasonable suspicion: Reasonable suspicion is a particularized, objective basis to suspect criminal activity, short of probable cause. It permits limited investigative stops but does not ordinarily justify an arrest or full search.
Illinois v. Gates: Illinois v. Gates is a 1983 U.S. Supreme Court decision adopting a totality-of-the-circumstances test for informant-based warrant applications. The decision explains how an informant's tip can contribute to probable cause without rigidly separate tests.
Beyond a reasonable doubt: Beyond a reasonable doubt is the high standard of proof required to convict a defendant in a criminal trial. Probable cause permits earlier investigative action and is far below the standard for conviction.
Search warrant: A search warrant is a judicial order authorizing a search of specified places or items. A judge ordinarily requires probable cause before issuing a search warrant.
Totality of the circumstances: The totality-of-the-circumstances approach evaluates evidence collectively rather than through a rigid checklist. Courts use this approach to decide whether facts establish probable cause.
Spinelli v. United States: Spinelli v. United States is a 1969 U.S. Supreme Court decision that assessed informant tips using two distinct considerations. Its stricter framework was replaced by the flexible approach later adopted in Gates.
Preponderance of the evidence: Preponderance of the evidence means that a claim is more likely true than not. This civil proof standard differs from probable cause in purpose and the decisions it governs.
Warrantless search: A warrantless search is a government search conducted without prior judicial authorization. Probable cause supports some warrantless searches, though an exception to the warrant requirement is also needed.
Affidavit: An affidavit is a written statement confirmed by oath or affirmation. Warrant applications commonly present the facts offered to establish probable cause in an affidavit.

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