The word prejudice refers to prejudgment, or forming an opinion before becoming aware of the relevant facts of a case. The word is often used to refer to preconceived, usually unfavorable, judgments toward people or a person because of gender, social class, age, disability, religion, sexuality, race/ethnicity, language, nationality or other personal characteristics. In this case, it refers to a positive or negative evaluation of another person based on their perceived group membership. Prejudice can also refer to unfounded beliefs and may include "any unreasonable attitude that is unusually resistant to rational influence." Gordon Allport defined prejudice as a "feeling, favorable or unfavorable, toward a person or thing, prior to, or not based on, actual experience.
The first psychological research conducted on prejudice occurred in the 1920s. This research attempted to prove white supremacy. One article from 1925 reviewing 73 studies on race concluded that the studies seemed “to indicate the mental superiority of the white race”. These studies, along with other research, led many psychologists to view prejudice as a natural response to inferior races.
In the 1930s and 1940s, this perspective began to change due to the increasing concern about anti-Semitism. At the time, theorists viewed prejudice as pathological and thus looked for personality syndromes linked with racism. Theodor Adorno believed prejudice stemmed from an authoritarian personality. Adorno described authoritarians as “rigid thinkers who obeyed authority, saw the world as black and white, and enforced strict adherence to social rules and hierarchies”. Adorno believed people with authoritarian personalities were the most likely to be prejudiced against groups of lower status.
In 1954, Gordon Allport linked prejudice to categorical thinking. Allport claimed that prejudice is a natural and normal process for humans. According to him, "The human mind must think with the aid of categories… Once formed, categories are the basis for normal prejudgment. We cannot possibly avoid this process. Orderly living depends upon it.
In the 1970s, research began to show that prejudice tends to be based on favoritism towards one’s own groups, rather than negative feelings towards another group. According to Marilyn Brewer, prejudice "may develop not because outgroups are hated, but because positive emotions such as admiration, sympathy, and trust are reserved for the ingroup."
In 1979, Thomas Pettigrew described the ultimate attribution error and its role in prejudice. The ultimate attribution error occurs when ingroup members "(1) attribute negative outgroup behavior to dispositional causes (more than they would for identical ingroup behavior), and (2) attribute positive outgroup behavior to one or more of the following causes: (a) a fluke or exceptional case, (b) luck or special advantage, (c) high motivation and effort, and (d) situational factors."
Do not prejudiced to others because of prejudice against another person can lead to conflict.