Collective action (CA) can foster social change in a society. While some authors argue that individuals’ beliefs about others’ protest participation increase own engagement (complementary strategy), others argue that individuals may also abstain from participation, because they see others as substitutes (substitutability strategy). In two experiments, using a self-persuasion technique, descriptive participation-norms were manipulated in the context of the Portuguese housing movement (Experiment 1: high vs. low, N=235; Experiment 2: high vs. control vs. low, N=330). CA-intentions were measured using general, conventional, non-normative and violent behaviors. Based on the Dual-Chamber Social Identiy Model of CA (SIMCA), we hypothesized that high-participation norms explain CA intentions and that these effects should be mediated by the relevant concepts of the model (identification, morality, injustice and efficacy). Contrary to our predictions, descriptive norms had no total effect on intentions to participate. Nevertheless, the whole SIMCA model mediated the relationship between descriptive norms and all CA intentions measures. Distinct specific indirect effects were found via politicized identification in Experiment 1 and via moral convictions in Experiment 2. As the reference group of participation-norms differed between the studies (young, Experiment 1; Portuguese, Experiment 2), we suggest that the relevance attributed to specific SIMCA factors is context and social identity dependent. Moreover, we speculate that individuals engage in strategic complementarity or substitutability according to their psychological motivations and others’ protest adherence, as well as their group membership. These results may have implications for how movements communicate their goals to the different audiences in the general public.

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Collective Action,Descriptive Norms,Dual-Chamber SIMCA model,Housing