Sole source rule is a common law principle that a plaintiff may not recover in a false-advertising action unless it demonstrates that it has a monopoly in the sale of goods possessing the advertised trait. Only on establishing monopoly does it become clear that the plaintiff would be harmed by the defendant's advertising.
Sole source rule is also used in criminal law. According to this rule, a defendant may be liable for false arrest even if he or she is not the arresting officer's sole source of information if the defendant goes beyond providing information and actually requests the arrest. If a defendant is the sole source of information, a lesser degree of instigation may be necessary for liability, but if the defendant is not the sole source, an actual request or command is necessary.[ Olinger v. Doe, 163 F. Supp. 2d 988, 991 (N.D. Ill. 2001)]