The Court in recent history has expressed a preference for a warrant in its decisions. Despite this expressed preference, the Court, by its deeds, has expanded on the opportunities for warrantless police activity. Exceptions to this preference must be justified and the scope of the warrantless searches should be limited to their justification. Historically, exceptions to requiring a search warrant were based on practicality concerns, primarily the concern that a warrant could not be secured in time to accomplish the objective of the search. Recent years have seen the basis for exceptions move from practicality concerns to such factors as a reduced expectation of privacy, as is the case with the automobile exception.
In analyzing various exceptions to the warrant requirement, we are reminded of the relationship between the two clauses of the Fourth Amendment discussed in the history section. United States v. Rabinowitz (1950) presents an excellent example of a debate between Justice Minton and Justice Frankfurter, which highlights the differing approaches to the Fourth Amendment. Minton, for the majority, maintained that the reasonable clause should be read separately and distinctly from the warrant clause so that the existence of a warrant was only one possible factor relevant to the reasonableness of a search. This interpretation viewed the existence of a warrant as important in determining reasonableness, but not as an absolute requirement. Frankfurter, in dissent, argued that the two clauses should be read together so that warrantless searches are per se unreasonable. Frankfurter's preference for a warrant stated that “searches conducted outside the judicial process, without prior approval by judge or magistrate, are per se unreasonable under the Fourth Amendment—subject only to a few specifically established and well-delineated exceptions” (This language was picked up in later cases, including Katz v. United States, 1967.)
In applying the Frankfurter analysis, exceptions to warrants were limited to the practicality concerns that required the warrant exception in the first place.