The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
The concept of
probable cause is central to the meaning of the warrant clause. Neither the Fourth Amendment nor the federal statutory provisions relevant to the area define
probable cause; the definition is entirely a judicial construct. An applicant for a warrant must present to the magistrate facts sufficient to enable the officer himself to make a determination of probable cause.
In determining what is probable cause . . . [w]e are concerned only with the question whether the affiant had reasonable grounds at the time of his affidavit . . . for the belief that the law was being violated on the premises to be searched; and if the apparent facts set out in the affidavit are such that a reasonably discreet and prudent man would be led to believe that there was a commission of the offense charged, there is probable cause justifying the issuance of a warrant.1 Probable cause is to be determined according to
the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.2 Warrants are favored in the law and their use will not be thwarted by a hypertechnical reading of the supporting affidavit and supporting testimony.3 For the same reason, reviewing courts will accept evidence of a less
judicially competent or persuasive character than would have justified an officer in acting on his own without a warrant.4 Courts will sustain the determination of probable cause so long as
there was substantial basis for [the magistrate] to conclude that there was probable cause.5