Final answer:
In social categorization, the most influential factor in formulating our attitudes towards others is their group membership, as it influences our perceptions and attitudes more than individual traits and is an integral part of socialization. This is also evident in how social groups shape political opinions and norms, reflecting group values more than individual experiences.
Step-by-step explanation:
According to the phenomenon known as social categorization, the factor most influential in helping us form an attitude about someone or something is c) Their group membership. Social categorization refers to the classification of people into groups based on shared characteristics. This process often influences how we perceive others and assess their behaviors. Studies in social psychology have shown that group membership can dramatically affect our attitudes and can be more influential than individual traits, such as physical appearance or verbal communication, because it relates to the wider context of an individual's social identity.The relevance of group membership is supported by the concept of socialization, which is the process by which individuals learn and internalize the values and norms of the groups they belong to. This includes political opinions, as our social groups, such as family and coworkers, significantly affect our stance on political issues. Moreover, informational social influence, which occurs when individuals are uncertain and the group has expertise, also underscores the power of group affiliations in shaping our attitudes and behaviors.Lastly, socializing within specific groups can lead to the adoption of the group's norms and opinions, a phenomenon observed across various social settings, from peer groups to professional environments. Thus, group membership stands out as a central factor in the development of individual attitudes in the context of social categorization.