Extract

are neither few nor well-delineated. The post-Warren Court has tended to focus on whether a search or seizure was reasonable, rather than on whether a warrant could or should have been obtained, and thus has tended to produce rulings that are case-specific rather than rule-oriented, with the result that neither a warrant nor probable cause is required in a large number of situations.

The oldest and most common reason given for forgoing a warrant is “exigency”—the concern that police or others will be harmed or that evidence will be destroyed if the police take the time to obtain a warrant. The most common reason given for permitting a search or seizure on less than probable cause is the perception that the action in question is relatively unintrusive. The modern tendency has been to define exigency broadly and intrusiveness narrowly. Other rationales for justifying particular exceptions to the warrant and probable cause standards include the minimal consequence of finding evidence of wrongdoing, the benign motives or lack of expertise of the enforcing government officials, the existence of other constraints that are thought to provide a sufficient substitute for a warrant, and, as the next section makes clear, tradition.

Of all of the routine police actions that implicate the Fourth Amendment, a custodial arrest—an arrest that results in the police taking the individual into custody for booking—is the most significant. But while such an arrest must be based on probable cause to believe the person...