What is the definition of a conspiracy?

A conspiracy must involve more than one person, even though all the conspirators may not either be identified, or be capable of being convicted. See for example O’Brien, supra; Guimond v. The Queen, 1979 CanLII 204 (SCC), [1979] 1 S.C.R. 960, 44 C.C.C. (2d) 481, 94 D.L.R. (3d) 1. Further, each of the conspirators must have a genuine intention to participate in the agreement. A person cannot be a conspirator if he or she merely pretends to agree. In O’Brien, Rand J. held at p. 670 that . . . a conspiracy requires an actual intention in both parties at the moment of exchanging the words of agreement to participate in the act proposed; mere words purporting agreement without an assenting mind to the act proposed are not sufficient. . . .