University of Chicago Law Review

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What facts are public and what facts are private? It is the fundamental, first-principles question in privacy law, and a necessary element in the two most important privacy torts, public disclosure of private facts and intrusion upon seclusion. This paper argues that insights from the literature on social networks and information dissemination can help provide courts with a coherent and consistent methodology for determining whether an individual has a reasonable expectation of privacy in a particular fact that he has shared with one or more persons. The social networks literature has generated theoretical and empirical insights about the probability that information disclosed to one member of a community will ultimately become known by a large segment of the community. Using these insights, courts can gauge whether the plaintiff's previously private information would have been widely disseminated regardless of the defendant's actions in a particular case. If so, the information in question was public, and if not, the tort law ought to deem the information private. This Article argues that such an approach, which treats the privacy question as an empirical one, is more attractive than any other method of establishing whether the plaintiff had a reasonable expectation of privacy in the information at issue.