It is a truth universally acknowledged, that a government in want of information must be in possession of a warrant. Or, if one prefers to quote the Warren Court, as do critics of NSA surveillance and the Patriot Act: "Searches conducted outside the judicial process, without prior approval by judge or magistrate, are per se unreasonable under the Fourth Amendment."

Well, sort of. Unless, that is, the police are in hot pursuit, or conducting a search incident to a lawful arrest, or have "reasonable suspicion" that a crime is about to be committed, or a suspect has given consent to a search, or a suspect's joint possessor (or roommate) has given consent--then no warrant is required. Or, come to think of it, unless federal administrators are checking whether a shop has followed minimum wage and maximum hour regulations, or a chemical company has complied with environmental regulations, or a liquor store's bookkeeping conforms to federal standards. Or unless the IRS wishes to see whether your income tax return squares with your bank records, or HHS wants to see if you have kept up your child support payments. Or unless you are visiting the House or the Senate or entering most any other government building. Or unless you are a high school student and the principal has reason to believe that you have cigarettes in your purse. Or unless you are hoping to board a plane, or a train, or to leave the country, or return to it. Each of these instances involves a government search; none requires a warrant.

In the 1967 case of Katz v. United States, Justice Potter Stewart qualified the "per se unreasonable" statement above by adding--"subject only to a few specifically established and well-delineated exceptions." But in the face of such pervasive, and hardly "well-delineated," examples of warrantless government searches, one must wonder if it isn't warrants that are the exception.

And indeed, if one consults the text and history of the Fourth Amendment, an exercise often disdained by the Warren Court, one will find that such is the case. Ironically, a more originalist reading reveals a Fourth Amendment that is better suited both to protecting civil liberties and to fighting the war on terror.

Start with the simple text of the Fourth Amendment, which contains two clauses, as emphasized in the formatting below:

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.

Note that these are independent clauses--the first concerning "unreasonable searches and seizures," the second concerning "warrants" and "probable cause." What is their relation to each other?

The Warren Court encouraged a "second clause dominant" approach. That is, the second clause defines what is meant by the first clause. What, under this approach, is a "reasonable search"? It is one in which a warrant has been issued by a judge upon probable cause, etc.