Keywords

Social identity theory was conceived and born as a theory of intergroup relations and conflict and cooperation between groups (Tajfel & Turner, 1979). As it developed, it became a much broader social psychological theory of the role of self and identity in group and intergroup phenomena in general (Turner, Hogg, Oakes, Reicher, & Wetherell, 1987). However, intergroup relations has always remained a core feature of the theory; for the simple reason that what happens within groups is inextricable from and fundamentally affected by what happens between groups, and vice versa.

Chapter 1 describes the core tenets of social identity theory and its key sub-theories. My account largely follows the historical development of the theory from its early roots in the 1970s through to the present day. Although I describe all aspects of the theory, I place a greater emphasis on its contribution to our understanding of the social psychology of peace and conflict in society. For detailed overviews of classic and contemporary social identity theory that incorporates all its conceptual developments and applications, see Abrams and Hogg (2010), Hogg (2006) and Hogg and Abrams (1988).

Some Historical Context

Social identity theory was initially developed at Bristol University in the UK in the 1970s by Henri Tajfel, who essentially integrated his early classic scientific work on categorisation and social perception (e.g. Tajfel, 1969) with his passion to understand prejudice, discrimination, and intergroup conflict in society. Tajfel was a Polish Jew who lost his entire family to the holocaust. He himself survived the war because he was a student at the Sorbonne in Paris at the outbreak of war in 1939 and enrolled in the French army. He was captured; and instead of being categorised as Jewish and sent to a concentration camp and certain death, he was categorised as French and survived the war in prisoner-of-war camps. Social categorisation and its consequences had an existential personal significance for Tajfel.

Tajfel and those he worked with to develop social identity theory also believed that the dynamics of prejudice and intergroup conflict were best understood as group phenomena generated by basic human motivations and cognitive processes impacted by people’s beliefs about themselves, and about the society, social context, and immediate situations people find themselves and their groups in (Abrams & Hogg, 2004; also Billig, 1976).

Authoritarian Personality and the Frustration-Aggression Hypothesis

The rise of Nazism in Europe in the 1930s seemed to some social psychologists to be at least partly explained as a collective response to frustrated nationalism. To explain the underlying psychology, Dollard and his colleagues (Dollard, Doob, Miller, Mowrer, & Sears, 1939) developed their psychodynamic-based frustration-aggression hypothesis . Frustrated goals leave people in a state of heightened goal-oriented arousal that can only be dissipated through aggression—and typically the aggression is vented on those who are weak and different because they are easier targets. Group frustrations are thus directed as aggression on weaker or minority groups.

The ensuing Second World War cost about 60 million lives (3 % of the world’s population), including the Nazi’s systematic extermination of six million Jews and five million non-Jews. To post-war social psychologists, the behaviour of the Nazi regime seemed like collective pathology, so they invoked Freudian psychodynamic notions to explain how this might have arisen. According to Adorno and his colleagues (Adorno, Frenkel-Brunswik, Levinson, & Sanford, 1950), authoritarian child-rearing practices in Germany created a love–hate relationship between children and their parents that produced people with authoritarian personalities who worshipped power, authority, and conformity and redirected their hatred onto those who were weak and different.

These two analyses of prejudice, discrimination and intergroup aggression have had a high profile for decades due to their intuitive and popular appeal. However, early social identity theorists felt these approaches were limited (Billig, 1976). They felt that personality would only play a small role in prejudice (the main cause of prejudice was the fact of living in a culture of prejudice—see Pettigrew, 1958); and the link between frustration and group aggression was not a mechanical summation of individual frustrations and aggression—rather, it required group-membership-based processes of communication to construct and represent an ideology identifying and representing certain groups as causes of frustration and targets of aggression.

Realistic Conflict Theory

In the 1950s and 1960s, the dominant social psychological theory of intergroup conflict in general was Muzafer Sherif’s realistic conflict theory (Sherif, 1966). The theory claims that individuals have goals, sometimes quite elaborate goals, and configure their behaviour to achieve their goals. Many goals are mutually exclusive (e.g. securing a job); only one person can achieve it at the expense of the other, and so people compete, sometimes fiercely. Some individual goals, however, are difficult to achieve without help from others (e.g. building a house). In these latter situations, people are dependent on others to work cooperatively with them to achieve their goals. People are promotively interdependent, and to the extent that others cooperate with them to help them achieve their goals they grow to like them and develop bonds of mutual attraction that create a cohesive social group (cf. Hogg, 1993)

Sherif, however, was most interested in the situation where groups have goals. He argued that when two groups have a mutually exclusive goal that only one group can achieve at the expense of the other group (e.g. world domination) then the groups compete, typically very fiercely. This is often accompanied by destructive intergroup behaviour and derogatory intergroup attitudes—the foundations of prejudice and discrimination and ultimately dehumanisation. In contrast, when two or more groups have a shared goal that can only be achieved by intergroup cooperation (e.g. fighting off a dangerous common foe) intergroup relations are less competitive and can even be cooperative and harmonious.

Categorisation and Discrimination: The Minimal Group Paradigm

Tajfel felt there was much to like in Sherif’s more context-dependent approach to intergroup conflict ; it certainly had better explanatory reach than dysfunctional personality and individualistic frustration-aggression approaches. However, he wondered whether something much more fundamental than competitive goal relations might be sufficient to generate differential in-group–out-group behaviour . Perhaps, the mere fact of being categorised as a member of a group was enough to lay the groundwork for intergroup conflict .

To investigate this proposition Tajfel and his collaborators designed an intriguing research paradigm, the minimal group paradigm (Tajfel, 1970; Tajfel, Billig, Bundy, & Flament, 1971). They ran a series of classic experiments in which British schoolboys, participating in what they believed was a study of decision making, were assigned to one of two groups completely randomly, but allegedly on the basis of their expressed preference for paintings by the artists Vassily Kandinsky or Paul Klee. The children knew only which group they themselves were in (Kandinsky group or Klee group), with the identity of out-group and fellow in-group members concealed by the use of code numbers. The children then individually distributed money between pairs of recipients identified only by code number and group membership. This pencil-and-paper task was repeated for a number of different pairings of an in-group and an out-group member, excluding self, on a series of distribution matrices carefully designed to tease out the distribution strategies that were being used.

The results showed that against a background of some fairness, the children who had been categorised, in contrast to those who had not been categorised, strongly favoured their own group. This was a startling finding as the groups were indeed minimal. They were created on the basis of a flimsy criterion, had no past history or possible future, the children did not even know the identity of other members of each group, and no self-interest was involved in the money distribution task as self was not a recipient. Subsequent experiments were even more minimal in character—simply randomly categorising participants as members of X-group or Y-group (e.g. Billig & Tajfel, 1973).

Over the past 45 years, literally hundreds of minimal group experiments have been conducted across the globe with a very wide range of participants. The robust finding is that the mere fact of being categorised as a group member produces ethnocentrism and competitive intergroup behaviour (e.g. Diehl, 1990). Other studies have shown that there is an asymmetry—categorised individuals favour the in-group rather than discriminate against the out-group, unless they feel that the in-group is under threat, in which case full-blown out-group discrimination also emerges (Mummendey & Otten, 1998). There is also a suggestion that minimal intergroup categorisation can generate in-group bias at the implicit level and is thus an effect over which people may have no conscious control (Otten & Wentura, 1999). Minimal groups have become a core feature of social identity research—a Google Scholar search in July 2015 yielded 9310 publications referring to minimal groups.

Social Identity Theory

Social identity theory crystalised around an attempt to explain the minimal group findings; bringing together Tajfel’s other scientific research on categorisation and social perception, and his social issues-oriented concern to explain prejudice, discrimination, and conflict in society (Tajfel & Turner, 1979; see Hogg & Abrams, 1988). At the core of the theory was Tajfel’s classic definition of social identity as an “individual’s knowledge that he belongs to certain social groups together with some emotional and value significance to him of this group membership” (Tajfel, 1972, p. 292). Social groups, whether large demographic categories or small task-oriented teams, provide their members with a shared identity that prescribes and evaluates who they are, what they should believe and how they should behave. Social identities also, very critically, highlight how the in-group is distinct from relevant out-groups in a particular social context.

Intergroup Relations

Social identity theory initially focused primarily on intergroup relations—exploring the issue of conflict and cooperation between large-scale social categories. This early emphasis within the wider theory is often referred to as the social identity theory of intergroup relations (Tajfel & Turner, 1979).

Social identity defines and evaluates one’s self-concept and how one will be treated and thought of by others. For this reason, when people make comparisons between their own group and an out-group they are concerned to ensure that their own group is positively distinctive—clearly differentiated from and more favourably evaluated than relevant out-groups. Intergroup comparisons are intrinsically in-group-favouring and ethnocentric (Brewer & Campbell, 1976), and intergroup behaviour is effectively a struggle over the relative status or prestige of one’s in-group. Higher status groups fight to protect their evaluative superiority; lower status groups struggle to shrug off their social stigma and promote their positivity .

The strategies that groups adopt to manage their identity depend on subjective belief structures —members’ beliefs about the nature of the relationship between their group and a specific out-group (e.g. Ellemers, 1993; Hogg & Abrams, 1988). Beliefs focus on status (what is my group’s social standing relative to the out-group?), stability (how stable is this status relationship?), legitimacy (how legitimate is this status relationship?), permeability (how easy is it for people to change their social identity by “passing” into the out-group?), and cognitive alternatives (is a different intergroup relationship conceivable?).

A social mobility belief structure hinges on a belief in permeability; that intergroup boundaries are effectively soft and easy to cross. It causes members of lower status groups as isolated individuals to disidentify from their group to try to join and gain acceptance by the higher status out-group—they try to “pass”. In reality, intergroup boundaries are rarely permeable and passing is unsuccessful, leaving those who attempt it in social identity limbo; excluded by both groups. Dominant groups often promulgate an ideology of social mobility and tolerate limited passing because it undermines and prevents collective action on the part of the minority.

A social change belief structure hinges on recognition that permeability is actually low; that intergroup boundaries are in fact hard and difficult to cross. It causes low status groups to engage in social creativity—behaviours aimed at redefining the social value of their group and its attributes, coupled with attempts to avoid (upward) comparison with higher status groups and instead engage in (lateral or downward) comparisons with other groups lower in the social pecking order. Dominant groups can sometimes promulgate a social change belief structure that encourages lateral or downward comparisons and competition among subordinate groups—an often very effective strategy of “divide and conquer”.

Where a social change belief structure is coupled with recognition that the social order is illegitimate group members can develop cognitive alternatives (essentially a critical ideology and road map for the plausible achievement of social change) and engage in social competition —direct competition with the out-group over status, which can range from debate through protest, to revolution and war .

But what about cooperation between groups, reduction of ethnocentrism and prejudice and the emergence of social harmony? Perhaps the problems of intergroup behaviour can be overcome by integrating warring factions into a cosy single superordinate group; thereby transforming conflictual intergroup behaviour into harmonious intragroup behaviour (e.g. Gaertner & Dovidio, 2000). Sadly, this can be very difficult to achieve or sustain. People are often strongly attached to their social category membership and associated identity; there is a deep “cultural divide” between groups (Prentice & Miller, 1999). Attempts to encourage superordinate re-categorisation can be viewed as an identity threat that is resisted, often fiercely (e.g. Hogg & Hornsey, 2006).

More effective is crossed-categorisation, where people acquire a more textured and less identity-threatening representation of in-group–out-group relations ; the groups are categorically distinct and separate but share identity on other dimensions (Crisp & Hewstone, 2007). Also effective is a multicultural framing of intergroup relations in which group distinctiveness is celebrated as a valued facet of a diverse society (Hornsey & Hogg, 2000), or construction of an intergroup relational identity in which groups actually partially define their own group in terms of their group’s mutually cooperative relations with an out-group (Hogg, 2015). In all these cases, some form of superordinate leadership may be needed—and that can pose a very real challenge.

Self-Categorisation

The early 1980s witnessed a very significant development of social identity theory to revisit and specify more precisely the social cognitive bases of social identity phenomena, as part of a more general social identity theory of the group often referred to as self-categorisation theory (Turner et al., 1987; see Abrams & Hogg, 2010).

Human groups are categories that people mentally represent as prototypes—fuzzy sets of interrelated attributes (attitudes, behaviours, customs, dress, and so forth) that capture overall similarities within groups and overall differences between groups. Prototypes represent attributes that maximise the group’s entitativity—the extent to which a group appears to be a distinct and clearly defined entity. One way to think of a group prototype is what comes immediately to mind if, for example, I said to you “French”, “hipster”, or “terrorist”. If many people in one group share their prototype of their own or another group the prototype is essentially a stereotype—if you alone believe that all Martians have skinny green bodies and huge heads it’s a prototype, but if pretty much all other humans believe this then the prototype is also a stereotype.

Overwhelmingly we make binary categorisations where one of the categories is the group that we are in, the in-group. Thus, in-group prototypes not only capture similarities within the in-group but also accentuate differences between our group and a specific out-group. In-group prototypes can therefore differ, typically around a relatively stable core, depending on what the comparison out-group is—in-group prototypes are influenced by the intergroup comparative context. Context-based changes can be transient but if the context change is enduring the prototype changes more profoundly and more enduringly.

The process of categorising someone has predictable consequences. Rather than “seeing” that person as an idiosyncratic individual, you see them through the lens of the prototype of the category you have placed them in—they become depersonalised in terms of the attributes of the prototype. They are matched to the prototype and assigned to varying degree its attributes. Categorisation-based depersonalisation affects in-group members and yourself in exactly the same way. When you categorise yourself, you view yourself in terms of the defining attributes of the in-group (self-stereotyping), and since prototypes also describe and prescribe group-appropriate ways to think, feel, and behave, you think, feel, and behave group prototypically. Your own behaviour conforms to in-group norms. In this way, self-categorisation not only transforms one’s self-conception but also produces normative behaviour among members of a group .

Social Identity Motivations

Social identity processes and phenomena are associated with two main motivational dynamics. The original social identity theory of intergroup relations (Tajfel & Turner, 1979) focused on positive intergroup distinctiveness and self-enhancement. One of the most distinctive features of group life and intergroup relations is that groups and their members go to great lengths to protect or promote their belief that “we” are better than “them”. Members strive for evaluatively positive intergroup distinctiveness because self is defined and evaluated in group terms and therefore the status, prestige, and social valence of the group attaches to oneself.

The pursuit of positive social identity may reflect one of the most basic of human motives for self-enhancement and self-esteem (Sedikides & Strube, 1997). Thus, positive distinctiveness and the dynamics of group and intergroup behaviour may be motivated by self-esteem with the implication that low self-esteem motivates group identification and intergroup behaviour, and identification elevates self-esteem—the self-esteem hypothesis (Abrams & Hogg, 1988; Rubin & Hewstone, 1998). Research suggests, however, that (a) group-based self-esteem is more closely associated than individual-level self-esteem with social identity processes and phenomena, (b) self-esteem can be raised by group identification but low self-esteem is a less reliable cause of identification (high self-esteem people often identify more strongly—e.g. Leary & Baumeister, 2000), and (c) people are exceedingly adept at buffering themselves against the self-evaluative consequences of low status or stigmatised group membership (e.g. Crocker, Major, & Steele, 1998). See Martiny and Rubin (2016) for a review.

Although self-categorisation theory focused on cognitive process and representation rather than motivation (Turner et al., 1987), it contained within it intimations of a more epistemic categorisation-based motivation associated with social identity dynamics. Uncertainty–identity theory (Hogg, 2007, 2012) is based on the premise that feeling uncertain about our world and in particular how to behave and how others will behave can be unsettling, even aversive. Uncertainty makes it difficult to predict and plan behaviour in such a way as to be able to act efficaciously. Not surprisingly people try to reduce uncertainty about their perceptions, attitudes, feelings, and behaviours. We are particularly motivated to reduce uncertainty if we feel uncertain about things that reflect on or are relevant to self, or if we are uncertain about self per se; about our identity, who we are, how we relate to others, and how we are socially located. Ultimately, people need to know who they are, how to behave, and what to think, and who others are, how they might behave, and what they might think.

Social categorisation is particularly effective at reducing uncertainty because it furnishes group prototypes that describe how people (including self) will and ought to behave and interact with one another. Such prototypes are relatively consensual (“we” agree that “we” are like this and “they” are like that)—thus, one’s worldview and self-concept are validated. Social categorisation renders one’s own and others’ behaviour predictable and thus allows one to avoid harm and plan effective action. It also allows one to know how one should feel and behave.

The more self-conceptually uncertain one is the more one strives to belong, particularly to groups that effectively reduce uncertainty—such groups are distinctive, with high entitativity and simple, clear, prescriptive, and consensual prototypes. In extreme circumstances, these groups might be orthodox and extremist, possess closed ideologies and belief systems, and have hierarchical leadership and authority structures (Hogg, 2014).

Ideological and authoritarian belief systems , whether secular or religious, are often associated with conditions of social uncertainty and instability (cf. Hogg, Adelman, & Blagg, 2010). Thus, to the extent that such belief systems are tied to group memberships, identification may mediate the link between social uncertainty and ideology. Another implication of uncertainty–identity theory is that subordinate groups may acquiesce in their subordinate status precisely because challenging the status quo elevates self-conceptual uncertainty to unacceptable levels (cf. Jost & Hunyadi, 2002). Indeed, although people prefer to identify with high than low status groups this preference can disappear under high uncertainty. Where people are self-conceptually uncertain, they are motivated by uncertainty reduction to identify equally with low or high status groups (Reid & Hogg, 2005).

A third motivational dynamic, which may be more closely related to uncertainty reduction than self-enhancement, is optimal distinctiveness (cf. Leonardelli, Pickett, & Brewer, 2010). People try to strike a balance between two conflicting motives, for inclusion/sameness (satisfied by group membership) and distinctiveness/uniqueness (satisfied by individuality), in order to achieve optimal distinctiveness. Smaller groups over-satisfy the need for distinctiveness, so people strive for greater inclusiveness, while large groups over-satisfy the need for inclusiveness, so people strive for distinctiveness within the group. One implication of this idea is that people should be more satisfied with membership of mid-size than very large or very small groups.

Social Norms, Influence, and Leadership

Social identity is expressed through normative behaviour. Norms map the contours of groups and social identities and are cognitively represented as group prototypes that describe and prescribe identity-defining behaviour (cf. Hogg & Smith, 2007). Within a given group there is usually substantial agreement on in-group and out-group prototypes—“we agree that we are like this and they are like that”. Self-categorisation produces conformity to in-group norms (normative behaviour) because, as described above, it assimilates self to the in-group prototype (see Abrams & Hogg, 1990). Conformity is not surface behavioural compliance, but a deeper process whereby people internalise and enact the group’s prototype.

Because in-group norms not only capture intragroup similarity but also accentuate intergroup distinctiveness they tend to be polarised away from the out-group and thus are often ideals that are more extreme than the group as a whole—conformity through self-categorisation often produces group polarisation (e.g. Abrams, Wetherell, Cochrane, Hogg, & Turner, 1990).

The social influence process associated with identification-contingent conformity is referent informational influence (Turner et al., 1987; see Abrams & Hogg, 1990). In groups, people are highly vigilant for and attentive to reliable information about the context-appropriate group prototype/norm. Typically, the most immediate and reliable source of this information is identity-consistent behaviour of those members who are generally considered to be most prototypical of the group. Once the norm has been recognised or established, it is internalised as the context-specific in-group prototype to which people conform through self-categorisation.

This process endows prototypical members with greater influence than non-prototypical members within the group—a point that serves as the foundation of the social identity theory of leadership (Hogg & Van Knippenberg, 2003; Hogg, Van Knippenberg, & Rast, 2012), see also Reicher, Haslam, Platow, and Steffens (2016). Although norms are the source of influence within groups, some members embody group norms better than others—they are more prototypical and are thus disproportionately influential. Prototypical members occupy a de facto leadership role in the group; and leaders who are prototypical are more influential and effective as leaders than are less prototypical leaders. Their effectiveness is amplified because they are assumed to be strongly identified with the group and are thus trusted to be acting in the group’s best interest and unlikely to do the group harm. Paradoxically, this allows them to diverge from group norms more than less prototypical leaders—they can be normatively innovative, which is a hallmark of leadership (Abrams, Randsley de Moura, Marques, & Hutchison, 2008).

Differentiation Within Groups

Group norms capture and express intragroup similarity. However, groups are almost always internally differentiated. One key differentiation that has far-reaching consequences is differentiation in terms of perceived prototypicality. We have already seen that prototypically central members are more influential than less prototypical members. Less prototypical members, particularly those who are prototypically marginal, are not liked or trusted much by the group, and are therefore not only relatively uninfluential but can be viewed with suspicion as deviants who potentially threaten the group (Marques, Abrams, Páez, & Hogg, 2001). Indeed, people on the normative boundary between in- and out-group, particularly if they are generally not very likeable individuals, are disliked more and are more strongly rejected if they are in-group than out-group members —they are treated as “black sheep” (Marques & Páez, 1994).

Overall, according to the theory of subjective group dynamics , reactions to marginal members stem from the fact that marginal members can threaten the normative clarity and integrity of the group (Marques, Abrams, & Serôdio, 2001; Pinto, Marques, Levine, & Abrams, 2010). Thus, a marginal member who diverges from the group norm in a direction that leans away from the out-group (called pro-norm deviance ) accentuates intergroup distinctiveness and is therefore less normatively threatening than one who leans in a direction towards the out-group (called anti-norm deviance ) and blurs intergroup boundaries—the latter invites a more negative reaction from the group than the former.

Although marginal members are generally perceived and treated unfavourably, they may sometimes fulfil important social change functions for the group (Hogg & Wagoner, in press). For example, deviants can serve as in-group critics (e.g. Hornsey, 2005), or as minority groups that challenge the accepted wisdom of the majority (e.g. Nemeth & Staw, 1989). In both cases, it can be a struggle for marginal members to be heard, but their contribution to the group is, ultimately, constructive—minorities and critics are effectively trying to change the group’s identity from inside.

Marginal members can sometimes be very damaging to the group. Minorities that feel they have no voice within the group may ultimately fragment the group by forming a schism (Sani, 2005); and individuals who feel they are or are treated as peripheral members of a group that is important to their identity may become zealous extremists on behalf of the group in an attempt to be accepted by the group as loyal central members (Hogg & Wagoner, in press).

Crowds and Protests

Members of groups often gather together collectively to act in unison (see La Macchia & Louis, 2016). Large public gatherings of this nature are characterised as crowds, demonstrations, rallies, protests, and so forth. One popular view in social psychology is that crowds provide anonymity and strip away responsibility and accountability—people become deindividuated such that primitive antisocial aggressive instincts are no longer held at bay by societal norms (cf. Zimbardo, 1970).

The social identity model of deindividuation (SIDE model ) has challenged this perspective on crowd behaviour, arguing instead that crowd events are just like any other group phenomenon where people identify with a group and are depersonalised in terms of the group’s attitudinal and behavioural norms (Klein, Spears, & Reicher, 2007; Reicher, Spears, & Postmes, 1995). Depersonalisation means viewing yourself as a category representative rather than a unique individual and is associated with a change in identity, whereas deindividuation refers to a loss of identity that is associated with primitive antisocial and aggressive impulses.

According to the SIDE model, depersonalisation can produce antisocial and aggressive behaviour, but only if people identify with a group that has a prototype prescribing such behaviour (Postmes & Spears, 1998). Crowds can sometimes seem volatile, but this is because they are unusual events; members are uncertain about the context-appropriate normative behaviour of the group, so they seek guidance as they behaviourally triangulate on the appropriate norm. From a SIDE perspective crowds are purposive, norm-governed, goal-oriented intergroup events that often have a very salient and visible out-group. In this respect, they resemble collective protest and encounter many of the wider obstacles to social mobilisation.

The study of social protest is the study of how individual discontents are transformed into collective action—how and why do sympathisers become mobilised as activists or participants? Mobilisation reflects the attitude–behaviour relationship —sympathisers hold sympathetic attitudes towards an issue, yet these attitudes do not readily translate into behaviour (Klandermans, 1997). It also resembles a social dilemma; protest is generally for a perceived social good (e.g. equality) or against a perceived social ill (e.g. oppression), and since success benefits everyone irrespective of participation but failure harms participants more, it is tempting to free ride—to remain a sympathiser rather than become a participant. Leadership is critical in mobilising a group to take action. In particular, the leader needs to be viewed as a just person who can be trusted to be acting in the best interest of the group and its members. Ultimately, however, it is social identification that increases the probability of social action and collective protest (e.g. Stürmer & Simon, 2004; Van Zomeren, Leach, & Spears, 2012; Van Zomeren, Postmes, & Spears, 2008).

Conclusion

Chapter 1 has provided a brief overview of social identity theory, mapping its historical development since the original formulation in the 1970s. I have described both classic and contemporary aspects of the theory and have tried to place greater emphasis on aspects that are directly relevant to understanding peace and conflict in society. Social identity theory is a unified conceptual framework that explicates group processes and intergroup relations in terms of the interaction of social cognitive, social interactive, and societal processes, and places self-conception at the core of the dynamic.

The theory was born out of Tajfel’s scientific research on categorisation and social perception, his personal passion to explain prejudice and discrimination, and his opposition to the prevailing personality and individualistic explanations. The minimal group studies (e.g. Tajfel, 1970) provided a proximal platform for the original social identity theory of intergroup relations (Tajfel & Turner, 1979). This was broadened and more tightly cognitively grounded by Turner and his students as the social identity theory of the group/self-categorisation theory (Turner et al., 1987). The two main motivational processes associated with social identity theory are captured by the self-esteem hypothesis (see Abrams & Hogg, 1988) and by uncertainty–identity theory (Hogg, 2007)—optimal distinctiveness theory (e.g. Leonardelli et al., 2010) provides a third perspective on social identity motivation .

A key component of social identity theory is its analysis of the influence process responsible for the recognition, construction, and internalisation of group norms— referent informational influence theory (see Abrams & Hogg, 1990), and the role of leadership in this process—the social identity theory of leadership (Hogg et al., 2012). The fact that groups are internally differentiated into prototypically central and prototypically peripheral members has far-reaching consequences not only for leadership and influence but also for the psychology of inclusion and exclusion, as described by the theory of subjective group dynamics (e.g. Marques, Abrams & Serôdio, 2001). Finally, the SIDE model explains how identity, influence, and leadership processes interact to affect social mobilisation and collective action (e.g. Van Zomeren et al., 2008).

Regarding peace and conflict in society, the underlying dynamic is one in which people protect and promote the status and entitativity of social identities that are central and important to their self-concept. The way they do this is guided by what they believe is possible given the nature of their group’s position in society. Prototype-based leadership and the behaviour of and the group’s treatment of marginal and central group members play a key role in all of this.