The fourth amendment protects the security of people's "persons, houses, papers, and effects" in two distinct (if overlapping) ways. First, it requires a sufficiently weighty public interest before the government's agents are allowed to search or seize. Thus, for example, probable cause is required for arrest. Whatever uncertainty there may be in the phrase "probable cause" (and, for that matter, however indefinite the idea of "arrest" may have become), in this context, at least, the probable cause standard requires the demonstration of objective facts that point with some probability to the guilt for some particular offense of the person arrested. As the Supreme Court stated in its 1949 decision, Brinegar v. United States, "[p]robable cause exists where 'the facts and circumstances within their [the officers'] knowledge and of which they had reasonably trustworthy information [are] sufficient in themselves to warrant a man of reasonable caution in the belief that' an offense has been or is being committed [by the arrestee]." The governmental interest ultimately served by arrest is of course the enforcement of the criminal laws. The arrest brings the suspected wrong-doer to book, and it may also permit discovery of additional incriminating evidence. Yet the probable cause standard insists upon a sufficient likelihood that this interest will in fact be served before an arrest may be made. It assesses the relative worth of the opposing interests - the public interest in law enforcement and the individual's right to be left alone - and identifies when the one must give way to the other. It tolerates some but not too much risk of the arrest of the innocent. This is the interest-balancing role of the fourth amendment. Second, the fourth amendment also performs a discretion control function. Even when the governmental interest at stake might otherwise justify a search or seizure, that search or seizure may be illegal if allowing it would confer too broad a discretionary authority on the police. There is, it is thought, a separate evil in leaving the police too much discretion to decide on their own where to search and whom and what to seize, under their own perhaps unknowable standards or under no standards at all. The Brinegar opinion adverted to this idea when it mentioned that permitting arrests on less than probable cause would "leave law-abiding citizens at the mercy of the officers' whim or caprice." Anthony Amsterdam seems to have been ref erring to these two functions of the fourth amendment when he asked whether a fourth amendment that limits the opportunity for "indiscriminate searches" should not also be concerned "with discriminatory ones. "
William J. Mertens,
The Fourth Amendment and the Control of Police Discretion,
U. Mich. J. L. Reform
Available at: https://repository.law.umich.edu/mjlr/vol17/iss3/5