Conspiracy, a combination between two or more persons to perpetrate an unlawful act, or to do a lawful act by unlawful means. A person injured by conspiracy has an action at law for the damage done, as when a man is falsely indicted of a crime. In criminal law, conspiracy is a misdemeanour punishable by penal servitude. Few things are left so doubtful in law as the point when a combination for a common object becomes unlawful. Formerly, combinations by workmen to raise the rate of wages were conspiracy, but this is no longer so; and till lately, prevailing judicial opinion was that a trade-union was a 'conspiracy in restraint of trade.' See COMBINATION.
Conspiracy was defined in the reign of Edward I. by the Ordinance of Conspirators, which was aimed at persons binding themselves together to lay false indictments, and otherwise to obstruct the course of justice. But the word came in time to have a wider meaning, and almost every combination to do a criminal or even an unlawful act is now an indictable conspiracy (see COMBINATION). The vagueness of the law has placed considerable power in the hands of juries. Almost any act, however innocent, may be treated as a crime if the jury choose to impute it to some motive connected with an unlawful combination. Again, in proving a charge of conspiracy, the prosecution may begin by giving evidence of the existence of a general conspiracy, and such evidence may consist of acts of third parties with which the person accused had no connection. The judges also have exercised their own discretion in deciding whether the objects of a combination were 'contrary to good morals and public policy' or not. But if juries and judges have not always exercised their discretion wisely, it is to be remembered that such discretion must of necessity form part of the law of conspiracy. Acts which are comparatively harmless when done by one or two persons may become intolerably oppressive when they are committed by a large number of persons acting in concert. See PLOT, SEDITION.