The Fourth Amendment | National Constitution Center | Khan Academy

Hey, this is Kim from Khan Academy, and today I'm talking with some experts about the Fourth Amendment. This is the Fourth Amendment of the Bill of Rights, and the Fourth Amendment deals with unreasonable search and seizure.

So here's the official text of the amendment: "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."

To learn more about the Fourth Amendment, I talked to two law professors who specialize in criminal law: Professor Tracy Mears of Yale University and Professor Orrin Kerr of George Washington University. Professor Kerr is a particular expert in criminal procedure and computer crime.

"Professor Kerr, can you tell us a little bit about what the Fourth Amendment is and why the framers were interested in protecting these rights?"

"In particular, the Fourth Amendment is a ban on unreasonable searches and seizures by the government. It's something the framers were interested in because they wanted to limit the government's power. At the time of the framing, the English king had engaged in some pretty bad things that the framers wanted to stop, and one of those was raiding people's homes with what was called a general warrant. The general warrant was basically a warrant that said the police could go anywhere and look for anything without any limit."

I asked Professor Mears to explain a little bit more about general warrants. She's a professor at Yale Law School who specializes in criminal procedure and criminal law policy.

"They were a general warrant allowing these officials to search people's homes, places, papers—the kinds of things that the Fourth Amendment lists—in ways that people thought was not okay. The Fourth Amendment was primarily concerned with a couple of things: one, a case involving seditious libel investigation. It's a case called 'Intake,' and a warrant was issued authorizing Intic—that's the subject of the warrant—his arrest and the seizure of all of his books and papers, so that he could be prosecuted for seditious libel."

"That case isn't as well known as the second case, which is called the 'Writs of Assistance' case. Basically, the Writs of Assistance involved customs inspectors who were trying to crack down on smuggling that was affecting Boston's economy. To aid in that task, inspectors used writs of assistance that were issued by the king and authorized the inspectors both to draft assistance—hence the name Writs of Assistance—and to search any place where smuggled goods might be concealed. The framers wanted to put an end to that, and so they said 'no general warrants are allowed' and searches and seizures have to be reasonable."

"What that really means is the government can't just stop anyone, arrest anyone, or break into someone's house. There are limits as to what the government can do."

But what are those limits? What determines probable cause for a search, and what renders a search and seizure unreasonable?

"Yeah, what counts as unreasonable is a really big question. There are different answers, different courts have suggested, but the basic idea is that first, if the government has a valid warrant, a search or seizure is reasonable. If a warrant—a judge has signed off and said 'yeah, the government has probable cause to search this place for particular evidence,' then the government can do that."

"And then the Supreme Court has laid out a bunch of what they call exceptions to the warrant requirement, which are also reasonable searches. For example, if a person consents to a search, that's reasonable, or in the case of a car, a car can be searched without a warrant based on probable cause. That's called the automobile exception."

"There are rules that govern when the police can stop somebody temporarily. When the government needs an arrest, they need probable cause. There are basically all sorts of rules that the Supreme Court has laid out on a bunch of different cases that say what counts as an unreasonable search or seizure."

"The Supreme Court has said that probable cause means a fair probability that evidence will be found in a particular place or that a particular person committed a crime. Fair probability is the language now. That's not something the Supreme Court has said; you know, that's not 50%. That doesn't mean it's more probable than not; it just means there's pretty good reason to think that there's evidence in a particular place or a particular person committed a crime."

"So it doesn't mean a hunch; it doesn't mean the officer just had the idea pop into his head, but it also doesn't mean that the officer's certain. There's gotta be a pretty good reason, but not certainty, to think that person committed the crime or that there's evidence there."

But when I asked Professor Mears the same question, she wasn't convinced it was so easy to tell what counts as probable cause.

"So what counts as a true probable cause to issue a warrant upon?"

"Sorry, we can just skip this and let's take a second. I mean, I taught this today. You can't—these aren't questions that you can just simply answer. No one can actually. I mean, literally, I taught today the fact that there is no real law on what probable cause is; it's inherently a factual determination."

"So how does this work in practice?"

"I asked Professor Kerr if it's the case that a police officer has to convince a judge that there's probable cause to issue a warrant."

"Yeah, so it can come up in two ways. In some cases, the Supreme Court says that the police have to go to a judge first and get a warrant, and then they have to convince the judge that what they're about to do is based on probable cause. Then other cases come up when the government has searched first or arrested first, and then they come back with the evidence or come back with the person who was arrested, and then there's a hearing as to whether there was probable cause for the arrest that already occurred."

"So either way, the standards are the same—it's that fair probability idea, ultimately up to a judge whether the police were right or wrong in doing what they did."

"Interesting, so there is a little bit of prior leg work involved in some cases. What happens in cases when it might be really important to get evidence, say if there's a bomb threat?"

"There are some rules that allow searches or seizures without a warrant under what they call exigent circumstances. That basically means there was an emergency, so the government had to act without a search warrant. If there's a ticking time bomb that they think is going to go off in a package and they've got good reason to think there is this ticking time bomb in the package, they don't have to say 'hey, we're going to go find a judge,' because by the time they do that the bomb might have gone off. They can search that package under this exigent circumstances idea."

"So that's an exception to the rules. Although beyond that, there's no difference between a serious case and a less serious case under the Fourth Amendment. They're kind of all serious cases, so the courts have to follow and the police have to follow the same rules in less serious and more serious cases."

Professor Mears gave me an example of what seemed like a less serious case, but it's still a really interesting example of what counts as an unreasonable search and seizure.

"I'll give you one more case that I'm sure the high school students would love, and my students love it. It's a case where a person was sitting in a noodle shop in front of a window, eating a big bowl of clear soup with noodles. A police officer walks by the person eating the noodles and notices something floating in the bowl of noodles. So he enters the store where the person is eating the noodles, and the person has left temporarily the bowl of noodles to get a napkin or go to the bathroom or something, you know? The police officer approaches the bowl, picks up the person's spoon, and stirs the noodles to see if he can find anything, and some baggies of crack float to the top."

"Did the person have a reasonable expectation of privacy in their food—in their soup? How did they rule?"

"They ruled that the stirring was a search. So if it is a search, i.e., that you have a subjective interest in privacy in your soup that society is prepared to recognize as reasonable, then the police officer would have to get a warrant before stirring the soup."

This raises the question: where do I have Fourth Amendment rights? Are some locations protected and not others?

"The building block of the Fourth Amendment is really that you have Fourth Amendment rights in your home, in your pockets, in your packages, but you don't have Fourth Amendment rights outside. You don't have Fourth Amendment rights in what you're doing outside, or if the police want to walk on what they call open fields, you know, public streets. You don't have Fourth Amendment rights in that."

"So, thinking about how the Fourth Amendment applies just in the physical world, if the police want to break into your home, they need a search warrant. If the police want to watch you walk down the street, they don't need anything; it's not a search or a seizure. So they can do anything they want just watching you. If they want to arrest you, they need probable cause to believe you've committed a crime."

"Those are really the building blocks of the Fourth Amendment that go back to 18th century technology. And then the big question becomes: all right, well how do you update that to a modern world?"

"It's also the case that the Fourth Amendment applies to seizures—what police have to show before they arrest a person, or temporarily stop them, or briefly pat their body on the outside for weapons. All of those questions are Fourth Amendment questions, as are questions involving how much force police actually use to effect the arrest once we've decided that an arrest is legitimate."

"So, you know, we haven't talked about any of those questions, but the Fourth Amendment governs all of that. And remember, the Fourth Amendment governs all of those topics in a context in which the framers' motivations for enacting the Fourth Amendment have absolutely nothing to do with most of those things I just mentioned."

"But the Fourth Amendment also has implications that go beyond warrants and seizures. Professor Mears thinks that one of the biggest Fourth Amendment issues today is discretion. Many people have thought much more about how the Fourth Amendment protects privacy than how the Fourth Amendment addresses discretion."

"And by discretion, in this case, you mean what they get to decide to do on their own?"

"Right, exactly. And one way to see the difference between those two things is to think about a metal detector in an airport. So long as everyone is required to go through the metal detector, there is no law enforcement discretion involved. So this is kind of where the public safety aspect comes in—that if we're all subject to non-invasive procedures at the whim of police, it's a little different than if individuals are kind of plucked for that reason."

"Right? That it's just pointing out that the targeting of people for invasions is a different problem than the invasion problem itself. And so if all we ever do is think about privacy invasion without thinking about the discretion problem, then we're missing something important."

For Professor Kerr, however, the most important issue at stake today regarding the Fourth Amendment is how it will apply to electronic media.

"Well, the big question, I think, is how the Fourth Amendment is going to apply to searches and seizures of computers, emails, the internet—new technologies that we all use every day. We wake up in the morning and hop online or go on Twitter or whatever you use online. Lots and lots of communications online all around the world, and how does the Fourth Amendment apply to that? It's something that the courts are beginning to answer, but they've only started to answer some really, really hard questions of kind of translating that physical world concept of the Fourth Amendment to the world of computers that we live in today."

So as we've learned, the Fourth Amendment ensures that government authorities can't raid homes, pockets, or papers without a warrant issued by a judge, and then only if there's probable cause to believe there's reason for a search.

What's tricky is deciding what counts as probable cause and whether it's discriminatory to select some people to search but not others. And how do we translate the Fourth Amendment to a world where our papers are all digital? Should the police be permitted to search our cell phones, our browsing histories, our private social media profiles?

You can learn more about the Fourth Amendment by checking out the National Constitution Center's interactive constitution and Khan Academy's resources on U.S. government and politics.