Final answer:
The statement is true; an arrest under the Fourth Amendment must be based on probable cause to be legal. Probable cause is necessary for arrest warrants and warrantless arrests when an officer witnesses a misdemeanor or suspects a felony. There are certain exceptions when a warrant is not required.
Step-by-step explanation:
The statement that an arrest is a seizure under the Fourth Amendment and must be based upon probable cause to be legal is true. The requirement of probable cause applies to both arrest warrants and situations where warrants are not required. In most states, police can arrest someone suspected of a felony crime without a warrant if they have probable cause.
For minor crimes or misdemeanors, an arrest can occur without a warrant if the officer witnesses the crime. Additional situations where police may conduct searches or seizures without a warrant include when there is consent, exigent circumstances, or when evidence is in plain view.
The Fourth Amendment clearly states, "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized." Therefore, the basis for any legal arrest is the establishment of probable cause.