1) Sociolinguistics is the study of the relationship between language and society. It examines how social factors such as context, status, and function influence language variation and use.
2) People code switch and use different linguistic varieties depending on social context, including the participants, setting, topic, and function of the interaction. Formal contexts like religion or education use high varieties while informal settings use low varieties.
3) Languages shift when their speakers abandon them for a dominant language due to economic, social, or demographic factors. This can lead to language loss or even death when no one speaks it anymore.