Abstract:  The success of protest in achieving its original aims may depend primarily on the events’ extent which shape public opinion. Collective action may play a significant and indirect role in influencing social change through changing public opinion. Partly, the success of a movement may derive from mobilizing the public to perceive a current context as illegitimate and turning bystanders into supporters. Though there is vast literature on the psychological factors promoting collective action, little is known about how collective actions influence a broader non-protesting community. The obtained articles mainly focus on the processes or mechanisms underpinning bystanders’ support for the social movement. We explored the effects of three key factors in shaping bystanders’ endorsements. This paper contains three experiments conducted to examine our hypothesis that participants were presented in a news article describing an instance of social protest during these studies. The details of the news were different in each group. Study1 was a 2(claim legitimacy: high vs. low) × 2 (protest tactics: violent vs. non-violent) design. Study2 was a 2(claim legitimacy: high vs. low) × 2 (protest tactics: violent vs. non-violent) × 2(expectation of achieving goals: high vs. low) design. Participants were asked to indicate their perceptions of the claim legitimacy, their support for the protests and other questions. Study 3 followed the pattern of Study2, but the background event was different. Results of Study1 showed that protests with legitimate claims were more supported than those with illegitimate claims in contexts of non-violent tactics. Meanwhile, there was only marginal difference of endorsements between participants in high-legitimacy group and low-legitimacy group when collective actions were violent. Study2 showed that in context of violent tactics, participants’ expectations of achieving goals could moderate the relation between claim legitimacy and their endorsements for collective actions. Participants’ supports for violent actions were positively predicted by claim legitimacy when there were little possibilities to achieve goals. However, this effect didn’t exist when possibilities of achieving goals were high. While in contexts of non-violent tactics, expectations of achieving goals did not affect participants’ endorsements for collective action. Only the factor of claim legitimacy was effective. The results of sStudy3 revalidated the results of Study2. The conclusions of the research is as following. First, legitimacy of the claims is the primary factor affecting bystanders’ support for collective action. Only when the protest’s aims accord with moral standards of the public will it gain the endorsements of public. Second, the use of violent tactics could even reduce bystanders’ endorsements of those protests with very legitimate claims. Violence may be seen as an action of alienation from the mainstream,which undermines the broader perceived legitimacy of a movement. Third, low possibility of achieving goals could inspire bystanders’ endorsements of violent collective actions when the claims are legitimate. Bystanders will lower their hostilities toward violence when they expect it will be very hard to achieve legitimate claims.

Key words: collective action, bystander, claim legitimacy, non-violent action, violent action