Speakers form and establish a pidgin language when two or more speakers who do not speak a common language form an intermediate third language. On the other hand, speakers practice code-switching when they are each fluent in both languages. Code mixing is a thematically related term, but the usage of the terms code-switching and code-mixing varies. Some scholars use either term to denote the same practice, while others apply code-mixing to denote the formal linguistic properties of said language-contact phenomena, and code-switching to denote the actual, spoken usages by multilingual persons.
In the 1940s and the 1950s many scholars called code-switching a sub-standard language usage. Since the 1980s, however, most scholars have recognized it is a normal, natural product of bilingual and multilingual language use.
In popular usage outside the field of linguistics the term code-switching is sometimes used to refer to relatively stable informal mixtures of two languages, such as Bangla or Hindi, or to refer to dialect or style-shifting, such as that practiced by speakers of African American Vernacular English as they move from less formal to more formal settings.
Why is code-switching
Code-switching relates to, and sometimes indexes social-group membership in bilingual and multilingual communities. Some sociolinguists describe the relationships between code-switching