Civil conspiracy, sometimes confused with aiding and abetting, is traditionally defined as a “combination of two or more persons for the purpose of accomplishing by concerted action either an unlawful purpose or a lawful purpose by unlawful means” where an overt tortious or unlawful act is committed in furtherance of the conspiracy.

[C]ivil conspiracy is not independently actionable and requires more than mere agreement. Civil conspiracy requires the performance of some underlying tortious act. No matter how atrocious, conspiracy itself does not give rise to a civil cause of action unless a tort has been committed and that tort results in damage.

The often-repeated definition is concededly opaque, but one needs to start somewhere to provide meaning to the abstractions.

Since civil conspiracy is derived from its criminal analog, reference to the law of criminal conspiracy is illustrative. According to the United States Supreme Court, the plurality element of a criminal conspiracy charge represents a “distinct evil.” This stems from the notion (discussed more fully below) that two people who agree to commit a crime are more dangerous than one or both of them planning to commit the same offense independently:

That agreement is a distinct evil, which may exist and be punished whether or not the substantive crime ensues. The conspiracy poses a threat to the public over and above the threat of the commission of the relevant substantive crime– both because the “[c]ombination in crime makes more likely the commission of [other] crimes” and because it “decreases the probability that the individuals involved will depart from their path of criminality.”

A civil conspiracy contains the same plurality-of-actors element but also requires a separate tort to be actionable.

Whether a conspiracy is an independent cause of action such as a tort or something different is the subject of confusion, and the language of the authorities is sometimes confusing as well. In some states, for example, it has been observed that “a conspiracy claim is ‘merely a mechanism for imposing vicarious liability; it is not itself a substantive basis for liability.”’ California has held that “[c]onspiracy is not a cause of action, but a legal doctrine that imposes liability on persons who, although not actually committing a tort themselves, share with the immediate tortfeasors a common plan or design in its perpetration.” Under Connecticut law, civil conspiracy is not an independent cause of action, but rather needs to be joined with a substantive tort; it “expands the universe of those potentially liable for the harm.” Arizona law is to the same effect as is Delaware law. “The essence of the civil conspiracy theory is not the actual conspiracy, but rather the civil wrong that causes an injury to another.”

But in other states, civil conspiracy has been termed an independent or substantive cause of action, although generally an independent tort must still be involved for liability to exist. Florida has held that conspiracy may be an independent tort where there is a “peculiar power of the conspirators” acting in unison; however, a question remains as to what that means. The “peculiar power” requirement has been criticized as being vague, lacking “adequate criteria” and being “difficult, if not impossible to apply.”Court decisions on civil conspiracy have been criticized for lack of clarity and repeating “tired phrases,” including such phrases as these.

Illinois is one of the states in which the language is unclear. Illinois authorities have recognized “a cause of action for civil conspiracy” and a “conspiracy claim.”But they have also observed that “conspiracy is not a separate and distinct tort in Illinois.” The same case recognizing civil conspiracy as a cause of action in Illinois also elaborated on the need to show a tortious act beyond an agreement in order to make out a claim for civil conspiracy. An Illinois treatise stated that “[t]here is no independent or separate tort for civil conspiracy” in Illinois, and yet still another Illinois case observed that civil conspiracy is an intentional tort. In some contexts, civil conspiracy, even if regarded as a separate cause of action, is not considered as tortious at all; and in others, it is referenced as a “derivative tort” because “recovery is not based on the conspiracy, i.e., the agreement, but on the injury from the underlying tort, here allegedly fraud.” Even where it is not considered a separate cause of action, however, conspiracy is nonetheless bound up with the law of torts since it typically rests on an underlying tort. Given this definitional problem, one can scarcely be blamed for being confused.

Source: Norman L. Greene. “Civil Conspiracy and the Rule of Law: A Proposal for Reappraisal and Reform.” 64 Ark. L. Rev. 301, pp. 331-337 (2011).