The Third Party Doctrine, and What Does the Fourth Amendment Do?:
Over at Technology Liberation Front, the Cato Institute's Jim Harper has an interesting response to my new Fourth Amendment paper, The Case for the Third Party Doctrine, forthcoming in the Michigan Law Review. Jim writes:
  My differences with Kerr are plentiful. Starting at the 30,000 foot level, my sense is that Kerr is treating the Fourth Amendment as a rule about criminal procedure. Oh sure, it’s classed that way in the legal academy, it has most of its application in criminal cases, and I first studied Fourth Amendment law in my constitutional criminal procedure class. But add this to the list of things I didn’t learn in law school: The touchstone of the Fourth Amendment is the security of the people—all of them—against unreasonable searches and seizures of their persons, houses, papers and effects. “The people” refers to all of us, the law-abiding citizens. . . .
  The welcome vision displayed in Katz counsels that the Fourth Amendment should naturally protect people as they come to use other instrumentalities — automated machinery owned by third parties, in particular — to expand the scope of their lives yet again. . . .Technological neutrality isn’t really relevant. What’s relevant is preserving the same security for people and their stuff that they should have in a free society.
  I think Jim has accurately identified a major gap between us: I treat the Fourth Amendment as a doctrine about criminal procedure, while Jim treats it as a way of ensuring a free society. The two approaches lead to very different criteria for analyzing Fourth Amendment rules. My approach generally focuses on whether rules pragmatically balance public safety and civil liberties in a regime backed by the exclusionary rule, whereas Jim's approach looks to what is necessary to protect civil liberties and generally assumes that other legal mechanisms can take care of public safety concerns.

  The interesting question is, where are we getting our understandings of what the Fourth Amendment means? My own view is candidly descriptive: I think this is what the Fourth Amendment means because this is what the Justices and the judges think it means. The notion of the Fourth Amendment as a tool of reasonable criminal procedures is, in my view, the basic post-Katz understanding of the Fourth Amendment held almost universally by the people with the robes. My general approach is to work within the consensus understanding held by the rulemakers and to think about how to apply that understanding rather than to change it.

  But is this really the correct way to interpret the Fourth Amendment? Is this the true Fourth Amendment? Well, if you're an originalist, it's not really close to the original meaning of the Fourth Amendment, as Professor Davies has persuasively argued. (.pdf) It's a lot closer to the original meaning of the Fourth Amendment than Jim Harper's "free society" concept. But in my experience, the real judges and Justices that make the rules don't really think about such things. They approach the Fourth Amendment as a tool of criminal procedure, and for a lot of reasons there's not much that can be done to change that.

  I think that explains much of the gap between the judges and the scholars in the area of the Fourth Amendment. Many scholars are greatly drawn to Jim's notion of the Fourth Amendment as a guarantor of a free society. I suspect many criminal procedure scholars are drawn to this notion because many crimpro scholars are strongly civil libertarian. If given a choice between a constitutional rule ensuring a free society and a constitutional rule requiring only reasonable police practices in criminal investigations, a civil libertarian presumably would pick the former.

  But the judges see themselves doing something very different; they see themselves figuring out the rules of criminal investigations. As a result, judges normally find most Fourth Amendment scholarship pretty unhelpful. For the most part, the scholarship isn't aware of their world: it imagines a Fourth Amendment that they don't see, and it doesn't often connect with the realities of the one that they do. One goal of my own work in the Fourth Amendment is to help push the scholarship to engage more with the world of the judges, and The Case for the Third-Party Doctrine is an example of a paper that I hope helps to do that.