The Supreme Court has assumed that the fundamental purpose of the
Fourth Amendment is to protect both property and privacy: property
from search and seizure and privacy from invasion. At the same time,
the Court has refused to accept arguments that the Fourth Amendment
simply transferred the laws concerning trespass into the Constitution. As a
general rule, the Court has found that government officials must have a
warrant before trespassing on some private real estate, while other private
real estate is open to invasion without either a warrant or probable cause.
Drawing the line between these two types of private real estate has been a major task for the Court.

In the 1924 case of Hester v. United States, two federal revenue agents hid in
the bushes on Charlie Hester's farm to witness the sale of moonshine whis-
key. While this act was technically a trespass on private property, a unani-
mous Supreme Court did not see this as a violation of the Fourth Amend-
ment. The agents were in an "open field," not inside a building or near the
house. Over the next 50 years, as the Supreme Court modified many of its
interpretations of the Fourth Amendment, scholars wondered if this "open
fields" doctrine still commanded a majority on the Court.

The Supreme Court revisited this issue 60 years later in the 1984 case of
Oliver v. United States, with Justice Powell writing the opinion for the six-
justice majority. In this case Kentucky state police drove through a field on a

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