groups will remain separate and will stereotype each other and discriminate against each other. In some cases, simply the perception that goals are zero-sum, whether they are or not, can increase prejudice. Therefore, not only is there a need for non-zero-sum goals, but they must be perceived as such. Complementarity Superordinate goals are not as effective when both groups are performing similar or the same roles within the group to achieve the goal. If this is the case, both groups may see the other as infringing on their work or getting in the way. It is considered to be more effective to have members of each group playing complementary roles in the achievement of the goal, although the evidence to support this idea is mixed. Absence of Trust or Inequality of Power Some also argue that with an absence of trust, the prospect of working together to achieve a mutual goal may not serve to bring groups to a superordinate identity. In some cases, when there are inequalities of power or a lack of trust among groups, the idea that they must work together and foster trust and positive interdependence may backfire and lead to more discrimination rather than less. Competing Theories Social categorization theory and social identity theory differ from realistic group conflict theory in that they suggest that people do not only belong to groups to gain material advantage. Therefore, these theories propose other ways of improving intergroup social relations. Social Categorization Theory Social categorization theory proposes that people naturally categorize themselves and others into groups, even when there is no motive to do so. Supporting this idea is Tajfel's minimal group paradigm, which has shown there is discrimination among groups created in a laboratory that have no history, future, interaction, or motivation. Social categorization suggests that intergroup competition may be a feature of this tendency to categorize and may arise without zero-sum goals. Under Tajfel's paradigm, people will go as far as hurting their own group in order to harm the other group even more. Thus, superordinate goals may not solve all forms of discrimination. Social Identity Theory Social identity theory proposes that not only do people naturally categorize themselves and others, but they derive part of their own identities from being a part of a social group. Being part of a social group is a source of positive self-esteem and motivates individuals to think of their