Weak > Strong: The Ironic Effect of Argument Strength on Supportive Advocacy

A great deal of research has tested the effect of argument quality—or message strength—on persuasion (for reviews see Petty & Wegener, 1998; Petty, Rucker, Bizer, & Cacioppo, 2004). This vast literature consistently shows that, when argument quality does exert an impact on persuasion (e.g., under conditions of high message processing), strong arguments produce more persuasion than do weak arguments. The present research suggests that under some conditions the opposite strategy may be superior—in particular, presenting weak rather than strong arguments might motivate greater advocacy and action. Across three studies, we show that when individuals already agree with a cause (i.e., it is pro-attitudinal), receiving weak arguments in its favor can prompt them into advocating more on its behalf. Perceived argumentation efficacy mediates this effect such that people exposed to weak arguments are more likely to feel they have something valuable to contribute. Moreover, consistent with the notion that it is driven by subjective feelings of increased efficacy, the effect is more likely to emerge when initial argumentation efficacy and attitude certainty are moderate or low. Individuals with high argumentation efficacy and high certainty generally advocate regardless of the strength of arguments received.