The two tiers consist of probable cause and reasonable suspicion. The model's purpose is to limit police discretion by supplying these officers with workable standards regarding the level of justification required to support particular intrusions. The first tier, probable cause, is required specifically by the Constitution only for searches and seizures conducted pursuant to the warrant clause of the fourth amendment. However, the Court has applied the probable cause standard to all seizures of persons that are equivalent in degree of intrusiveness to an arrest and to all full-scale searches. The second tier, reasonable suspicion, is a less stringent standard than probable cause. Recent decisions (Adams v. Williams, Gerstein v. Pugh, and United States v. Cortez) by the Court have weakened this two-tier model considerably. The model no longer represents an effective guideline for police intrusions. Instead, it sanctions limited intrusions upon little evidence. Moreover, it permits more severe intrusions upon a probable cause standard that requires less than a preponderance of the evidence. This standard is imprecise, nebulous, and difficult for the police to implement and for courts to review. Behind this transformation is the Court's distaste for the exclusionary rule. Excluding tainted evidence often results in the exoneration of guilty persons. This concern, however, does not justify the Court's elimination of fundamental constitutional requirements. Society consists of innocent and guilty persons alike, both deserving the protections that the fourth amendment is designed to provide. A total of 193 footnotes are supplied. (Author summary modified)