The Model Penal Code, troubled by the expansive definition of conspiracy provided by the common law and by many early-twentieth-century American state statutes, requires that the object of the agreement must be a crime for conspiracy to be committed. Most states, though not necessarily using the specific language of the MPC, have followed its policy choice and require that the object of the agreement be a crime.
But beware! Some states still define conspiracy in the old-fashioned sweeping manner. California, for example, defines conspiracy as an agreement of two or more people “[t]o commit any act injurious to the public health, to public morals, …” Cal. Penal Code §182(a)(5).
At common law, conspiracy, like attempt, merged into the completed substantive offense. Consequently, conspirators could not be punished both for conspiracy and the target offense.
Today, however, in most jurisdictions conspiracy is a separate substantive offense. Unlike solicitation and attempt, conspiracy does not merge with the object crimes. The rationale supporting this antimerger rule is straightforward. Conspiracy criminalizes the act of agreeing to commit a crime and beginning to actually implement that agreement; the target offense punishes the separate behavior of actually committing the offense agreed upon. Thus, generally speaking, conspirators can be (1) convicted of both the crime of conspiracy and of target crimes actually committed in furtherance of the conspiracy, and (2) sentenced to consecutive (rather than concurrent) sentences for both conspiracy and the target offense.
Conspiracy once was commonly punished with a fixed term without regard to the seriousness of the crime the conspirators planned to commit. Today, however, most jurisdictions either set the punishment at some term less than the object crime or follow the MPC.
The Model Penal Code sets the punishment for conspiracy at the same grade and degree as the most serious object crime, except that a conspiracy to commit a capital offense or a felony of the first degree is punished as a felony of the second degree. MPC §5.05(1). The MPC considers a criminal group to be especially dangerous. Consequently, the deterrent impact of punishment must be harsh to be effective. Critics of this approach argue that, if the conspirators have been arrested before they have accomplished their criminal goal, they should be punished less severely because they have not done as much harm.