Supreme Court of the United States
Illinois v. Lance Gates
Decided June 8, 1983 – 462 U.S. 213
Justice REHNQUIST delivered the opinion of the Court.
This totality-of-the-circumstances approach is far more consistent with our prior treatment of probable cause than is any rigid demand that specific “tests” be satisfied by every informant’s tip. Perhaps the central teaching of our decisions bearing on the probable cause standard is that it is a “practical, nontechnical conception.” “In dealing with probable cause, … as the very name implies, we deal with probabilities. These are not technical; they are the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.” Our observation in United States v. Cortez, 449 U.S. 411, 418 (1981) regarding “particularized suspicion,” is also applicable to the probable cause standard:
“The process does not deal with hard certainties, but with probabilities. Long before the law of probabilities was articulated as such, practical people formulated certain common-sense conclusions about human behavior; jurors as factfinders are permitted to do the same—and so are law enforcement officers. Finally, the evidence thus collected must be seen and weighed not in terms of library analysis by scholars, but as understood by those versed in the field of law enforcement.”
As these comments illustrate, probable cause is a fluid concept—turning on the assessment of probabilities in particular factual contexts—not readily, or even usefully, reduced to a neat set of legal rules. Informants’ tips doubtless come in many shapes and sizes from many different types of persons.
Moreover, the “two-pronged test” directs analysis into two largely independent channels—the informant’s “veracity” or “reliability” and his “basis of knowledge.” There are persuasive arguments against according these two elements such independent status. Instead, they are better understood as relevant considerations in the totality-of-the-circumstances analysis that traditionally has guided probable cause determinations: a deficiency in one may be compensated for, in determining the overall reliability of a tip, by a strong showing as to the other, or by some other indicia of reliability.
If, for example, a particular informant is known for the unusual reliability of his predictions of certain types of criminal activities in a locality, his failure, in a particular case, to thoroughly set forth the basis of his knowledge surely should not serve as an absolute bar to a finding of probable cause based on his tip. Likewise, if an unquestionably honest citizen comes forward with a report of criminal activity—which if fabricated would subject him to criminal liability—we have found rigorous scrutiny of the basis of his knowledge unnecessary. Conversely, even if we entertain some doubt as to an informant’s motives, his explicit and detailed description of alleged wrongdoing, along with a statement that the event was observed first-hand, entitles his tip to greater weight than might otherwise be the case. Unlike a totality-of-the-circumstances analysis, which permits a balanced assessment of the relative weights of all the various indicia of reliability (and unreliability) attending an informant’s tip, the “two-pronged test” has encouraged an excessively technical dissection of informants’ tips, with undue attention being focused on isolated issues that cannot sensibly be divorced from the other facts presented to the magistrate.
Notes, Comments, and Questions
The Gates Court rejects the Aguilar-Spinelli test’s insistence on using two specific measures to compose a (somewhat) mathematical formula for probable cause. As the Court explains, the existence of probable cause will not be found by entering “veracity” and “basis of knowledge” into a formula which yields the total weight of evidence presented to a magistrate.
As the Court puts it:
“This totality-of-the-circumstances approach is far more consistent with our prior treatment of probable cause than is any rigid demand that specific ‘tests’ be satisfied by every informant’s tip. Perhaps the central teaching of our decisions bearing on the probable cause standard is that it is a ‘practical, nontechnical conception.’”
When police have probable cause to believe either (1) that evidence of crime will be found in a particular place or (2) that a certain person has committed a crime, important police action becomes lawful that would have remained unlawful absent probable cause. One important example involves vehicle stops; police may stop a car based on probable cause to believe that its driver has committed a traffic law violation. It is widely believed that many officers use this power for reasons other than traffic enforcement—for example, stopping drivers who violate trivial traffic rules in the hope of discovering evidence of more serious lawbreaking. In addition, some critics of police allege that at least some officers use their traffic-stop authority in ways that constitute unlawful discrimination, such as on the basis of race. Based on these beliefs and allegations, motorists have sought review of vehicle stops, justified by probable cause, on the basis of police officers’ “real” or “true” reasons for conducting the stops. The Court has resisted engaging in such review.