Imagine you’re driving a car, and a police officer spots you and pulls you over for speeding. He orders you out of the car. Maybe he wants to place you under arrest. Or maybe he wants to search your car for evidence of a crime. Can the officer do that?
The Fourth Amendment is the part of the Constitution that gives the answer. According to the Fourth Amendment, the people have a right “to be secure in their persons, houses, papers and effects, against unreasonable searches and seizures.” This right limits the power of the police to seize and search people, their property, and their homes.
The Fourth Amendment is often in the news. Police in some cities have engaged in aggressive use of “stop and frisk.” In some cases, a police stop ends with officers or others firing their weapons. There is concern about the use of aerial surveillance, whether by piloted aircraft or drones. And AI algorithms are being used to mine data looking for suspicious activity.
The application of the Fourth Amendment to all these activities would have surprised those who drafted it, and not only because they could not imagine modern technologies like the Internet and drones. They also were not familiar with organized police forces like we have today. Policing in the eighteenth and early nineteenth centuries was a responsibility of the citizenry, which participated in “night watches.” Other than that, there was only a loose collection of sheriffs and constables, who lacked the tools to maintain order as the police do today.
The primary concerns of the generation that ratified the Fourth Amendment were “general warrants” and “writs of assistance.”. In England, the King employed “general warrants” to go after his political enemies, leading to the famous decisions in Wilkes v. Wood (1763) and Entick v. Carrington (1765). General warrants allowed the King’s messengers to break into the homes of the King’s critics and arrest them without probable cause that they had committed a crime. In those cases, judges decided that general warrants were illegal. Over in the colonies, the King’s officials used the writs of assistance—like general warrants, but often unbounded by time restraints—to search for goods on which taxes had not been paid. James Otis famously challenged the writs in a Boston court. Although he lost, some such as John Adams attribute this legal battle as the spark that led to the Revolutionary War. Both controversies helped support the idea that a person’s home is their castle, not easily invaded by the government.
Today the Fourth Amendment is understood as placing limits on the government whenever it detains or searches a person or property. The Fourth Amendment also provides that “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 idea is that to avoid the evils of general warrants, each search or seizure should be cleared in advance by a judge, and that to get a warrant the government must show “probable cause”—a certain level of suspicion of criminal activity—to justify the search or seizure.
The government can conduct a legal search if it has a valid warrant or else an exception to the warrant requirement applies. Police can search cars without warrants, they can detain people on the street without them, and they can always search or seize in an emergency without going to a judge.
The Fourth Amendment usually comes in court during a criminal prosecution. The Supreme Court has ruled that if the police seize evidence as part of an illegal search, the evidence normally cannot be admitted into court. This is called the “exclusionary rule.” It is controversial because in most cases evidence is being tossed out even though it shows the person is guilty and, as a result of the police conduct, they might avoid conviction. “The criminal is to go free because the constable has blundered,” declared Benjamin Cardozo (a famous judge and ultimately Supreme Court justice). But, responded another Supreme Court justice, Louis Brandeis, “If the government becomes the lawbreaker, it breeds contempt for the law.”
One of the difficult questions today is what constitutes a “search”? If the police standing in Times Square in New York watched a person planting a bomb in plain daylight, we would not think they needed a warrant or any cause. But what about installing closed circuit TV cameras on poles, or flying drones over backyards, or gathering evidence that you have given to a third party such as an Internet provider or a banker?
Another hard question is when a search is acceptable when the government has no suspicion that a person has done something wrong. Lest the answer seem to be “never,” think of airport security. Surely it is okay for the government to screen people getting on airplanes, yet the idea is as much to deter people from bringing weapons as it is to catch them—there is no “cause,” probable or otherwise, to think anyone has done anything wrong. This is the same sort of issue with bulk data collection, and possibly with gathering biometric information.
Whatever the right answers are, advancing technology and the many threats that face society means that the Fourth Amendment will continue to play a central role in the future.