An agreement between two or more persons to jointly commit either an unlawful act or an act which is lawful by unlawful means.
Model Penal Code Section 5.03. Criminal Conspiracy.
(1) Definition of Conspiracy. A person is guilty of conspiracy with another person or persons to commit a crime if with the purpose of promoting or facilitating its commission he:
(a) agrees with such other person or persons that they or one or more of them will engage in conduct which constitutes such crime or an attempt or solicitation to commit such crime; or
(b) agrees to aid such other person or persons in the planning or commission of such crime or of an attempt or solicitation to commit such crime.
(2) Scope of Conspiratorial Relationship. If a person guilty of conspiracy, as defined by Subsection (1) of this Section, knows that a person with whom he conspires to commit a crime has conspired with another person or persons to commit the same crime, he is guilty of conspiring with such other person or persons, whether or not he knows their identity, to commit such crime.
(3) Conspiracy With Multiple Criminal Objectives. If a person conspires to commit a number of crimes, he is guilty of only one conspiracy so long as such multiple crimes are the object of the same agreement or continuous conspiratorial relationship.
(4) Joinder and Venue in Conspiracy Prosecutions.
(a) Subject to the provisions of paragraph (b) of this Subsection, two or more persons charged with criminal conspiracy may be prosecuted jointly if:
(i) they are charged with conspiring with one another; or
(ii) the conspiracies alleged, whether they have the same or different parties, are so related that they constitute different aspects of a scheme of organized criminal conduct.
(b) In any joint prosecution under paragraph (a) of this Subsection:
(i) no defendant shall be charged with a conspiracy in any county [parish or district] other than one in which he entered into such conspiracy or in which an overt act pursuant to such conspiracy was done by him or by a person with whom he conspired; and
(ii) neither the liability of any defendant nor the admissibility against him of evidence of acts or declarations of another shall be enlarged by such joinder; and
(iii) the Court shall order a severance or take a special verdict as to any defendant who so requests, if it deems it necessary or appropriate to promote the fair determination of his guilt or innocence, and shall take any other proper measures to protect the fairness of the trial.
(5) Overt Act. No person may be convicted of conspiracy to commit a crime, other than a felony of the first or second degree, unless an overt act in pursuance of such conspiracy is alleged and proved to have been done by him or by a person with whom he conspired.
(6) Renunciation of Criminal Purpose. It is an affirmative defense that the actor, after conspiring to commit a crime, thwarted the success of the conspiracy, under circumstances manifesting a complete and voluntary renunciation of his criminal purpose.
(7) Duration of Conspiracy. For purposes of Section 1.06(4):
(a) conspiracy is a continuing course of conduct which terminates when the crime or crimes which are its object are committed or the agreement that they be committed is abandoned by the defendant and by those with whom he conspired; and
(b) such abandonment is presumed if neither the defendant nor anyone with whom he conspired does any overt act in pursuance of the conspiracy during the applicable period of limitation; and
(c) if an individual abandons the agreement, the conspiracy is terminated as to him only if and when he advises those with whom he conspired of his abandonment or he informs the law enforcement authorities of the existence of the conspiracy and of his participation therein.
Black’s Law Dictionary, 2nd Edition.
In criminal law. A combination or confederacy between two or more persons formed for the purpose of committing, by their joint efforts, some unlawful or criminal act, or some act which is innocent in itself, but becomes unlawful when done by the concerted action of the conspirators, or for the purpose of using criminal or unlawful means to the commission of an act not in itself unlawful. Pettibone v. U. S., 148 U. S. 197, 13 Sup. Ct. 542, 37 L. Ed. 419; State v. Slutz, 106 La. 182, 30 South. 298; Wright v. U. S., 108 Fed. 805, 48 C. C. A. 37; U. S. v. Benson, 70 Fed. 591, 17 C. C. A. 293; Girdner v. Walker, 1 Heisk. (Tenn.) 186; Boutwell v. Marr, 71 Vt. 1, 42 Atl. 607, 43 L. It. A. 803, 76 Am. St. Rep. 746; U. S. v. Weber (C. C.) 114 Fed. 950; Comm. v. Hunt, 4 Mete. (Mass.) Ill, 3S Am. Dec. 340; Erdman v. Mitchell, 207 Pa. 79, 56 Atl. 327, 63 L. R. A. 534, 99 Am. St. Rep. 7S3; Standard Oil Co. v. Doyle, US Ky. 602, 82 S. W. 271, 111 Am. St. Rep. 331. Conspiracy is aconsultation or agreement between two or more persons, either falsely to accuse another of a crime punishable by law; or wrongfully to injure or prejudice a third person, or any body of men, in any manner; or to commit any offense punishable by law; or to do any act with intent to prevent the course of justice; or to effect a legal purpose with a corrupt intent, or by improper means. Hawk. P. C. c. 72.
Encyclopedia Britannica, 11th Edition.
CONSPIRACY (from Lat. conspirare, literally to breathe together, to agree, combine, and especially to form a secret plot), in English law, an agreement between two or more persons to do certain wrongful acts, which may not, however, be punishable when committed by a single person, not acting in concert with others. The following are enumerated in text-books as the things, an agreement to do which, made between several persons, constitutes the offence of conspiracy: – (I) Falsely to charge another with a crime punishable by law, either from a malicious or vindictive motive or feeling towards the party, or for the purpose of extorting money from him; (2) wrongfully to injure or prejudice a third person or any body of men in any other manner; (3) to commit any offence punishable by law; (4) to do any act with intent to pervert the course of justice; (5) to effect a legal purpose, with a corrupt intent or by improper means; to which are added (6) conspiracies or combinations among workmen to raise wages.
The division is not a perfect one, but a few examples under each of the heads will indicate the nature of the offence in English law. First, a conspiracy to charge a man falsely with any felony or misdemeanour is criminal; but an agreement to prosecute a man who is guilty, or against whom there are reasonable grounds for suspicion, is not. Under the second head the textbooks give a great variety of examples, – e.g. mock auctions, where sham bidders cause the goods to go off at prices grossly above their worth; a conspiracy to raise the price of goods by spreading false rumours; a conspiracy by persons to cause themselves to be reputed men of property, in order to deceive tradesmen. These examples show how wide the law stretches its conception of criminal agreement. The third head requires no explanation. A conspiracy to murder is expressly made punishable by penal servitude and imprisonment (The Offences against the Person Act 1861). A curious example of conspiracy under the fourth head is the case in which several persons were convicted of conspiracy to procure another to rob one of them, so that by convicting the robber they might obtain the reward given in such cases. The combination to effect a lawful purpose with corrupt intent or by improper means is exemplified by agreements to procure seduction, &c.
The most important question in the law of conspiracy, apart from the statute law affecting labourers, is how far things which may be lawfully done by individuals can become criminal when done by individuals acting in concert, and some light may be thrown on it by a short statement of the history of the law. In the early period of the law down to the 17th century, conspiracy was defined by the Ordinance of Conspirators of 1305:” Conspirators be they that do confedr or bind themselves by oath, covenant, or other alliance, that every of them shall aid the other falsely and maliciously to indite, or cause to indite, or falsely to move or maintain pleas, and also such as cause children within age to appeal men of felony, whereby they are imprisoned and sore grieved, and such as retain men in the country with liveries or fees to maintain their malicious enterprizes, and this extendeth as well to the takers as to the givers.” The offence aimed at here is conspiracy to indict or to maintain suits falsely; and it was held that a conspiracy under the act was not complete, unless some suit had been maintained or some person had been falsely indicted and acquitted. A doctrine, however, grew up that the agreement was in itself criminal, although the conspiracy was not actually completed (Poulterer’s case, 1611). This developed into the rule that any agreement to commit a crime might be prosecuted as a conspiracy. A still further development of this doctrine is that a combination might be criminal, although the object apart from combination would not be criminal. The cases bearing on this question will be found arranged under the following heads, and in chronological order, in the Law of Criminal Conspiracies and Agreements, by R. S. Wright (London, 1873): – Combinations against government; combinations to defeat or pervert justice; combinations against public morals or decency; combination to defraud; combination to injure otherwise than by fraud; trade combinations. ” It is conceived,” says the author, ” that on a review of all the decisions, there is a great preponderance of authority in favour of the proposition that, as a rule, an agreement or combination is not criminal unless it be for acts or omissions (whether as ends or means) which would be criminal apart from agreement.” A dictum of Lord Denman’s is often quoted as supplying a definition of conspiracy. It is, he says, either a combination to procure an unlawful object, or to procure a lawful object by unlawful means; but the exact meaning to be given to the word ” lawful ” in this antithesis has nowhere been precisely stated. A thing may be unlawful in the sense that the law will not aid it, although it may not expressly punish it. The extreme limit of the doctrine is reached in the suggestion that a combination to hiss an actor at a theatre is a punishable conspiracy.
The application of the wide conception of conspiracy to trade disputes and to civil questions arising out of contracts for service is dealt with under the headings Labour Legislation, Strikes And Lock-Outs and Trade Unions. The criminal side is regulated by the Conspiracy and Protection to Property Act 1875, which enacted that an agreement or combination by two or more persons to do, or procure to be done, any act in contemplation or furtherance of a trade dispute between employers and workmen shall not be indictable as a conspiracy, if such act committed by one person would not be punishable as a crime. When a person is convicted of any such agreement or combination to do an act which is punishable only on summary conviction, and is sentenced to imprisonment, the imprisonment shall not exceed three months, or such longer period, if any, as may have been prescribed by the statute for the punishment of the said act when committed by one person.” The effect of the act of 1875 in conjunction with the Employers and Workmen Act of the same year is that breach of contract between master and workmen is to be dealt with as a civil and not as a criminal case, with two exceptions. A person employed on the supply of gas and water, breaking his contract with his employer, and knowing, or having reasonable cause to believe, that the consequence of his doing so, either alone or in combination with others, will be to deprive the inhabitants of the place wholly or to a great extent of their supply of gas or water, shall be liable on conviction to a penalty not exceeding £20, or a term of imprisonment not exceeding three months. And generally any person wilfully and maliciously breaking a contract of service or hiring, knowing or having reasonable cause to believe that the probable consequences of his so doing either alone or in combination with others will be to endanger human life or cause serious bodily injury, or to expose valuable property whether real or personal to destruction or serious injury, shall be liable to the same penalty. By section 7 every person who, with a view to compel any other person to abstain from doing or to do any act which such other person has a legal right to do or abstain from doing, wrongfully and without legal authority, (I) uses violence to or intimidates such other person, or his wife and children, or injures his property; or (2) persistently follows such other person about from place to place; or (3) hides any tools, clothes or other property owned or used by such other person, or deprives him of or hinders him in the use thereof; or (4) watches or besets the house or other place where such other person resides, or works, or carries on business, or happens to be, or the approach to such house or place; or (5) follows such other person with two or more other persons, in a disorderly manner, in or through any street or road, shall be liable to the before-mentioned penalties. Of course a combination to do any of these acts would be punishable as a conspiracy, as mentioned in section 3 above.
Seamen are expressly exempted from the operation of this act. The exceptions as to contracts of service for the supply of gas and water, &c., were supported by the circumstances of the London gas stokers’ case in 1872.
Conspiracy at common law is a misdemeanour, and the punishment is fine or imprisonment, or both, to which may be added hard labour in the case of any conspiracy to cheat and defraud, or to extort money or goods, or falsely to accuse of any crime, and to obstruct, pervert, prevent or defeat the cause of justice. Conspiracy to murder, whether the victim be a subject of the king or resident in his dominions or not, is, by the Offences against the Person Act 1861, punishable by penal servitude.
The most generally accepted definition of conspiracy in the United States is ” a combination of two or more persons by some concerted action to accomplish some criminal or unlawful purpose, or to accomplish some purpose not in itself criminal or unlawful by criminal or unlawful means “; though in some states, e.g.Colorado, it is not conspiracy under the statute to do a lawful act in an unlawful way (Lipschitz v. People  25 Col. 261). In some states an overt act must be shown (N.Y. Pen. Code, § 171). This is so in the Federal Courts, United States v.McCord (72 Fed. R. 159). Conspiracy out of the state to do any act which if done within the state would be treason is punishable by imprisonment not exceeding ten years (ibid. § 169). The United States Revised Statutes, § 544 0, make any conspiracy to commit an act, declared by any law of the United States to be a crime, an offence against the United States, e.g. a conspiracy to plunder a wrecked vessel within the admiralty and maritime jurisdiction of the United States (U.S. v. Sanche, 7 Fed. R. 715), conspiracy to violate the postal laws (Re Renkle 125 Fed. R. 996), to violate the revenue laws (U.S. v. Cohn  128 Fed. R. 615). It is not essential that the object be accomplished (Radford v. U. S. 129 Fed. R. 49). A conspiracy to depress the market price of stock by circulating false reports that the company was going into the hands of a receiver is indictable under N.Y. Pen. Code, § 168 (People v. Goslin  67 N.Y. App. D. 16, affirmed 171 N.Y. 627).