The Case for the Third Party Doctrine


I’m delighted to debate Greg Nojeim on the controversial third-party doctrine of Fourth Amendment law. He and I share a number of first principles: Both of us are looking for a way to apply the Fourth Amendment to new technologies in a sensible and balanced way. Our disagreement is on how to do that. Nojeim would reject the third-party doctrine, while I would apply the doctrine in some cases but not in other cases. In this contribution, I want to explain why I think the much-maligned third-party doctrine is a critical tool for applying the Fourth Amendment to new technologies in some cases, but that it should not be extended to all cases.
    My argument rests on the need to maintain the technological neutrality of Fourth Amendment protections. The use of third parties is akin to new technology, and that technology threatens to alter the balance of power struck by the Fourth Amendment. The third-party doctrine offers a way to maintain the balance of police power: It ensures that the same basic level of constitutional protection applies regardless of technology. Or so I will argue, drawing from two recent articles of mine: The Case for the Third-Party Doctrine, 107 Mich. L. Rev. 561 (2009), and Applying the Fourth Amendment to the Internet: A General Approach, 62 Stan. L. Rev. 1005 (2010).
    My argument begins with a thought experiment. Let’s start by imagining a world without third parties. If you want to send a package to a friend, you need to leave your home and carry it to your friend’s house. If you want to go to the doctor’s office, you need to visit it in person. In a world without third parties, you would need to venture out into the world on a regular basis to accomplish anything.
    Next, ask yourself how the Fourth Amendment would apply to police investigations in this world with no third parties. The rules would be simple. The police would need a warrant to enter your home, but they would be permitted to watch you in public. They could watch you leave your home, travel to the home of your friend, and disappear inside when you delivered your package. They could watch you leave your home, go to the doctor’s office, and disappear inside. All these steps would occur in public, where the Fourth Amendment offers no protection from the watchful eye of the police.
    Now let’s introduce third parties. Third parties allow individuals to do remotely what they would otherwise have to do in person. Instead of traveling to your friend to deliver the package, you can send the package through the postal mail. The postal network substitutes for your trip to your friend; instead of bringing your package to your friend, the mailman will do it. And instead of visiting the doctor in person, you could call the doctor on the phone. To borrow from the old advertising campaign for the Yellow Pages, you can “let your fingers do the walking.” In each case, the third-party service means you no longer have to leave your home.
    The critical point from the standpoint of Fourth Amendment law is that use of third parties introduces a substitution effect. In a world with no third parties, individuals often have to travel in public. The police can see when individuals leave their homes, where they travel, and when they arrive. Using third parties allows individuals to substitute a private transaction for that public transaction. Facts that used to be known from public surveillance are no longer so visible. By allowing individuals to use remote services, the use of third parties has brought outdoor activity indoors.
    The question for Fourth Amendment law is how to respond to this technological shift. In my view, the goal should be to apply the Fourth Amendment in a technologically neutral way. In a world with no third parties, the Fourth Amendment strikes a balance of police power: It gives the government the power to investigate crimes in some ways, but also limits the government’s investigations in important ways. I think that’s a sensible balance, as it tries to balance our shared interests in deterring crime and punishing wrongdoing (which can only occur if the police successfully gather evidence to prove cases) with our commitments to privacy and avoiding government abuses of power. If I’m right that this balance is proper, then it follows we should maintain it. We should try to apply the Fourth Amendment so that it offers the same basic protections and strikes the same balance in a world of third parties than it did in a hypothetical world without them.
    The third-party doctrine achieves that, in my view. The doctrine ensures that the Fourth Amendment applies to conduct that harnesses third parties in the same way it applies to events that occur without third-party help. It does so by matching the Fourth Amendment protection in the use of the third party with the Fourth Amendment protection that existed before.
    Smith v. Maryland is a good example. In Smith, a robbery victim was receiving harassing phone calls. The police suspected Smith, and they asked the phone company to install a pen register on his home phone line. Whenever a call was placed from Smith’s home phone, the phone company would record the numbers dialed and keep a record for the police. The record showed that the calls did indeed originate from Smith’s home, and the police used that evidence to get a warrant to search the home and prove Smith’s guilt. The question in the case was whether the numbers dialed were protected by the Fourth Amendment.
    Before we get to the Court’s reasoning in Smith, let’s imagine what constitutional protection would apply if Smith could not use third parties but wanted to harass the victim anyway. Smith would have been forced to harass the victim in person: He would have left his house, walked to his car, and driven to her home. If the police suspected that Smith was the harasser, they could have watched him the entire way: All of Smith’s conduct would have been exposed to public view without Fourth Amendment protection.
    The Court in Smith ruled that Smith had no reasonable expectation of privacy in his numbers dialed. That rule maintained the level of Fourth Amendment protection regardless of whether Smith used a third party to harass his victim. By holding that the use of the pen register did not constitute a search, the Court ensured that the police would have the same information either way. The time of the call, the originating number of the call, and the destination of the call are the informational equivalents of what the police would have learned by watching Smith in public if he had not used a third party. In other words, Smith could not change the balance of Fourth Amendment protection by using a third party; the Fourth Amendment offered the same level of protection either way.
    Importantly, my defense of the third-party doctrine implies an important limit: The doctrine should apply when the third party is a recipient of information, but it should not apply when the third party is merely a conduit for information intended for someone else. Put another way, the third-party doctrine should apply to the collection of non-content information in a network but not the contents of communications. The reason is that when the third party is merely a conduit for information, the information that is sent through the third party is not information that would have been revealed if no third parties had been used. In a world with no third parties, the message would remain private: If I bring you a sealed package in person, the government can’t open up the package without a warrant. That same rule should and does apply if the delivered communication takes the form of a sealed letter in the postal mail, the contents of a phone call, or the contents of an e-mail.
    Greg Nojeim makes several rejoinders to my approach. First, he argues that use of third parties is unavoidable in our modern world. That may be right, but the same was true about going out in public in the world without third parties. It would be unpersuasive to argue that the Fourth Amendment must protect what occurs in the public square because venturing out into the public square is unavoidable in our modern life. In my view, it is equally unpersuasive to claim that the Fourth Amendment must protect third-party substitutes because modern life requires their use.
    Second, Nojeim argues that surveillance is cheaper and easier today than it used to be, and, therefore, that there is more of a need for legal regulation. Cost and time used to limit the government and channel its resources into the more important investigations and away from abuses; if the costs and time of surveillance drop, more abuses are likely unless the law steps up its role. This may be right. But Nojeim does not say why we should rely on the courts, rather than Congress, for this source of law. In my view, statutes are ideally situated to provide the kind of counterweight Nojeim envisions. Statutes have the flexibility to offer a tailored and nuanced approach to limit government properly without the blunt instrument of the Fourth Amendment and the warrant requirement.
    Third, Nojeim suggests that it is arbitrary to apply the third-party doctrine to non-content information but then reject its application to the collection of contents. In his view, limiting the third-party doctrine to non-content information is “a chink in the armor” of the doctrine. But legal doctrines should apply to the extent of their rationale, and no further. Recognizing the validity of the third-party doctrine in some cases does not mean that it should logically apply to cases that are very different. In my view, countering the substitution effect of using third parties generates a sensible and reasonably clear rationale for both the presence of the third-party doctrine and its limits. To ensure the technological neutrality of the Fourth Amendment, we should apply the third-party doctrine where third parties generate substitution effects but not where they don’t. This means that courts should apply the third-party doctrine to the collection of non-content information, but should reject the doctrine when the government collects contents of communications.

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