Written by Chief Justice John Roberts. Joined by Justice Antonin Scalia
The rule the majority fashions does not implement the high office of the Fourth Amendment to protect privacy, but instead provides protection on a random and happenstance basis, protecting, for example, a co-occupant who happens to be at the front door when the other occupant consents to a search, but not one napping or watching television in the next room. And the cost of affording such random protection is great, as demonstrated by the recurring cases in which abused spouses seek to authorize police entry into a home they share with a nonconsenting abuser ...
The Fourth Amendment protects privacy. If an individual shares information, papers, or places with another, he assumes the risk that the other person will in turn share access to that information or those papers or places with the government. And just as an individual who has shared illegal plans or incriminating documents with another cannot interpose an objection when that other person turns the information over to the government, just because the individual happens to be present at the time, so too someone who shares a place with another cannot interpose an objection when that person decides to grant access to the police, simply because the objecting individual happens to be present ...
Today's opinion creates an exception to this otherwise clear rule: A third-party consent search is unreasonable, and therefore constitutionally impermissible, if the co-occupant against whom evidence is obtained was present and objected to the entry and search.
This exception is based on what the majority describes as "widely shared social expectations" that "when people living together disagree over the use of their common quarters, a resolution must come through voluntary accommodation." But this fundamental predicate to the majority's analysis gets us nowhere: Does the objecting cotenant accede to the consenting cotenant's wishes, or the other way around? The majority's assumption about voluntary accommodation simply leads to the common stalemate of two gentlemen insisting that the other enter a room first.
Nevertheless, the majority is confident in assuming--confident enough to incorporate its assumption into the Constitution--that an invited social guest who arrives at the door of a shared residence, and is greeted by a disagreeable co-occupant shouting " 'stay out,' " would simply go away. The Court observes that "no sensible person would go inside under those conditions," and concludes from this that the inviting co-occupant has no "authority" to insist on getting her way over the wishes of her co-occupant. But it seems equally accurate to say--based on the majority's conclusion that one does not have a right to prevail over the express wishes of his co-occupant--that the objector has no "authority" to insist on getting his way over his co-occupant's wish that her guest be admitted.
The fact is that a wide variety of differing social situations can readily be imagined, giving rise to quite different social expectations. A relative or good friend of one of two feuding roommates might well enter the apartment over the objection of the other roommate. The reason the invitee appeared at the door also affects expectations: A guest who came to celebrate an occupant's birthday, or one who had traveled some distance for a particular reason, might not readily turn away simply because of a roommate's objection. The nature of the place itself is also pertinent: Invitees may react one way if the feuding roommates share one room, differently if there are common areas from which the objecting roommate could readily be expected to absent himself. Altering the numbers might well change the social expectations: Invitees might enter if two of three co-occupants encourage them to do so, over one dissenter.
The possible scenarios are limitless, and slight variations in the fact pattern yield vastly different expectations about whether the invitee might be expected to enter or to go away. Such shifting expectations are not a promising foundation on which to ground a constitutional rule, particularly because the majority has no support for its basic assumption--that an invited guest encountering two disagreeing co-occupants would flee--beyond a hunch about how people would typically act in an atypical situation ...
A wide variety of often subtle social conventions may shape expectations about how we act when another shares with us what is otherwise private, and those conventions go by a variety of labels--courtesy, good manners, custom, protocol, even honor among thieves. The Constitution, however, protects not these but privacy, and once privacy has been shared, the shared information, documents, or places remain private only at the discretion of the confidant ...

