Wharton’s rule is a rule that prohibits the prosecution of two persons for conspiracy to commit a particular offense when the offense in question can only be committed by at least two persons. i.e., an agreement by two or more persons to commit a particular crime cannot be prosecuted as a conspiracy if the crime could not be committed except by the actual number of participants involved.
This criminal law rule is named after Francis Wharton, an American criminal law author, who formulated it. It is also known as concert-of-action rule. The essence of the rule is that an agreement by two persons to commit a particular crime cannot be prosecuted as a conspiracy when the crime is of such a nature as to necessarily require the participation of two persons for its commission. All the actors may be charged with conspiracy if an additional person participates so as to enlarge the scope of the agreement. When legislative intent is to impose a separate punishment for conspiracy to commit a particular crime, Wharton's Rule does not apply.
When a plurality of offenders is necessary to the idea of an offense, e.g., adultery, bigamy, or dueling, conspiracy cannot be charged because it would evade the statutory limitation on the punishment for the offense. It is a judicial presumption to be applied in the absence of legislative intent to the contrary. Wharton's Rule applies only to offenses that require concerted criminal activity, a plurality of criminal agents. [Iannelli v. United States, 420 U.S. 770, 785 (U.S. 1975)]
Classic examples of Wharton's rule offenses are: dueling, bigamy, adultery, pandering, gambling, buying and selling contraband goods, giving and receiving bribes.