conspiracy, in law, agreement of two or more persons to commit a criminal or otherwise unlawful act. At common law, the crime of conspiracy was committed with the making of the agreement, but present-day statutes require an overt step by a conspirator to further the conspiracy. It is not necessary for guilt that the act be fully consummated. Many acts that would not be criminal if accomplished by an individual alone may nevertheless be the object of a conspiracy. With the rise of the labor movement in the 19th cent., British and American courts used this legal consent against unions; courts held that while an individual employee might lawfully abstain from work, the concerted stoppage of a group of employees, as in a strike, might be criminal. In 1875, Britain passed a law exempting unions from prosecution for conspiracy, and in 1932 the U.S. Congress passed a law that limited the power of federal courts to restrain union activity. Other controversial aspects of conspiracy laws include the modification of the rules of evidence and the potential for a dragnet. A statement of a conspirator in furtherance of the conspiracy is admissible against all conspirators, even if the statement includes damaging references to another conspirator, and often even if it violates the rules against hearsay evidence. The conspiracy can be proved by circumstantial evidence. Any conspirator is guilty of any substantive crime committed by any other conspirator in furtherance of the enterprise. It is a federal crime to conspire to commit any activity prohibited by federal statute, whether or not Congress imposed criminal sanctions on the activity itself. An individual injured by a conspiracy may sue the conspirators to recover damages.

Pazzi conspiracy, 1478, plot against Lorenzo de' Medici (Lorenzo il Magnifico) and his brother Giuliano, designed to end the hegemony of the Medici in the Florentine state and to enlarge papal territory. It was instigated by Pope Sixtus IV, his nephew Gerolamo Riario, Archbishop Salviati, and members of the Pazzi family, a wealthy Florentine family that rivaled the Medici. Actually, the Pazzi were tools in the conspiracy, which aimed not only at the death of the Medici, but at the elevation of Riario to power in Florence. Details of the plot were worked out by Salviati and the Pazzi while Riario and the pope remained in Rome. On Apr. 26, during High Mass at the cathedral, Giuliano de' Medici was stabbed to death, while Lorenzo escaped with a wound. The enraged Florentines seized and killed the conspirators. The Medici remained firmly entrenched in power.

Cato Street Conspiracy: see Thistlewood, Arthur.

Amboise, conspiracy of, 1560, plot of the Huguenots (French Protestants) and the house of Bourbon to usurp the power of the Guise family, which virtually ruled France during the reign of the young Francis II. The plan, presumably worked out by Louis I de Bourbon, prince de Condé, provided for a march on the castle of Amboise, the abduction of King Francis II, and the arrest of François, duc de Guise, and his brother Charles, cardinal of Lorraine. The cardinal was forewarned, and the rebels, beaten before they had united their forces, were ruthlessly massacred. For weeks the bodies of hundreds of conspirators were hanging from the castle and from every tree in the vicinity. The Huguenots were enraged. A brief period of conciliation followed under the chancellorship of Michel de L'Hôpital, appointed by the king's mother, Catherine de' Medici. He temporarily halted Protestant persecution until the outbreak (1562) of the Wars of Religion.

Agreement between two or more persons to commit an unlawful act or to accomplish a lawful end by unlawful means. Some U.S. states require an overt act in addition to the agreement to constitute conspiracy. Individual conspirators need not even know of the existence or the identity of all other conspirators. In a chain conspiracy the parties act separately and successively (as in distributing narcotics). A civil conspiracy is not prosecuted as a crime but forms the grounds for a lawsuit. In antitrust law, conspiracies in restraint of trade (e.g., price fixing) are rigorously prosecuted. In the U.S. it is common to punish a conspiracy to commit an offense more harshly than the offense itself, but there has been a growing trend to follow the European example and make the punishment for conspiracy the same as or less than that for the offense itself.

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(April 16, 1478) Unsuccessful plot to overthrow the Medici rulers of Florence. It was led by the rival Pazzi family, with the backing of Pope Sixtus IV, who wanted to consolidate papal rule over northern central Italy. The conspirators tried to assassinate two Medici brothers during mass at the Cathedral of Florence; they killed Giuliano de' Medici, but Lorenzo de' Medici escaped. The people of Florence rallied to the Medici and killed many of the conspirators, leaving Lorenzo more powerful than before and setting off a two-year war with the papacy.

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