What are the elements of conspiracy and what is the effect of conspiracy?

Taschereau J. in Regina v. O’Brien (1954), 1954 CanLII 42 (SCC), 110 C.C.C. 1 (S.C.C.) describes the elements involved in conspiracy in the following passages at pp. 3-4: The two elements of agreement and of common design are specifically stated to be essential ingredients of the crime of conspiracy. Willes J. in Mulcahy v. The Queen (1868), L.R. 3 H.L. 306 at p. 317, said: "A conspiracy consists not merely in the intention of two or more, but in the agreement of two or more to do an unlawful act, or to do a lawful act by unlawful means. So long as such a design rests in intention only, it is not indictable. When two agree to carry it into effect, the very plot is an act in itself, and the act of each of the parties ... punishable if for a criminal object." The definition of conspiracy itself supposes an aim. People do not conspire unless they have an object in view. The law punishes conspiracy so that the unlawful object is not attained. It considers that several persons who agree together to commit an unlawful act, are a menace to society, and even if they do nothing in furtherance of their common design, the state intervenes to exercise a repressive action, so that the intention is not materialized, and does not become harmful to any one. The intention must necessarily be present because it is the unlawful act necessarily flowing from the intention, that the state wishes to prevent.