The fourth amendment to the Constitution has two basic clauses. The first, the reasonableness clause, protects the people against unreasonable searches and seizures. The second, the warrant clause, sets forth conditions under which a warrant may issue. Searches and seizures made pursuant to a warrant are, quite obviously, governed by the commands of the warrant clause. However, the effect of the warrant clause upon searches and seizures made without warrants is not clear from the amendment itself, and the Supreme Court has failed to develop a consistent interpretation of the proper role of that clause.
Mack Allen Player,
Warrantless Searches and Seizures
Available at: http://digitalcommons.law.uga.edu/fac_artchop/36