What must a plaintiff prove to establish that a member of a group is liable for the actions of the group?

A number of cases have considered what a plaintiff must prove to establish that a member of a group is liable for the actions of the group. In Wilson v. Switlo, 2011 BCSC 1287, Punnett J. summarized the legal principles as follows: 173 I draw the following conclusions from the above decisions: a) the fact that a member of the group may approve of what the group is doing is not sufficient to establish responsibility for the publication. That is, mere sympathy for the aims of the group is not sufficient to impose liability; b) the plaintiffs must establish on a balance of probabilities that each defendant was actively involved in the content and publication of each of the impugned words. A purely mechanical contribution is not sufficient; c) depending on the nature of the group, a court may infer from a member’s participation in a group involved in a campaign of publications that the member intended and encouraged the publications. However, evidence of a different motive for participation may generate an alternative inference.