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The language of the provision which became the Fourth Amendment underwent some modest changes on its passage through the Congress, and it is possible that the changes reflected more than a modest significance in the interpretation of the relationship of the two clauses. Madison's introduced version provided "The rights to be secured in their persons, their houses, their papers, and their other property, from all unreasonable searches and seizures, shall not be violated by warrants issued without probable cause, supported by oath or affirmation, or not particularly describing the places to be searched, or the persons or things to be seized." As reported from committee, with an inadvertent omission corrected on the floor, the section was almost identical to the introduced version, and the House defeated a motion to substitute "and no warrant shall issue" for "by warrants issuing" in the committee draft. The word "secured" was changed to "secure" and the phrase "against unreasonable searches and seizures" was reinstated. In some fashion, the rejected amendment was inserted in the language before passage by the House and is the language of the ratified constitutional provision.

Not every incident where an officer ascertains information is considered a "search." An officer who views something which is publicly viewable, for instance, by looking through the window of a house from the street, is not conducting a "search" of the house. In Katz v. United States (1967), the Supreme Court ruled that there is no search unless an individual has an "expectation of privacy" and the expectation is "reasonable" - that is, it is one that society is prepared to recognize. So, for example, there is generally no search when officers look through garbage because there is no expectation that garbage is private. Similarly, there is no search where officers monitor what phone numbers an individual dials, although Congress has placed statutory restrictions on such monitoring. This doctrine sometimes leads to somewhat unexpected results; in Florida v. Riley (1989), the Supreme Court ruled that there was no expectation of privacy, and thus no search, where officers hovered in a helicopter 400 feet above a suspect's house and conducted surveillance. The Supreme Court has also ruled that there can be no expectation of privacy in illegal activity. Therefore, investigations that reveal only illegal activity, such as some use of drug sniffing dogs, are not searches.

The decision in Terry v. Ohio (1968) established that some brief seizures may be made without probable cause. If an officer has a reasonable suspicion that a crime has been committed or will soon be committed, that