Contact is a significant concept in sociolinguistics — social contact and language contact. Language change spreads through networks of people who talk to one another. Tight-knit groups that keep to themselves do not tend to promote change. Networks whose members also belong to other networks tend to promote change. People can be neighbours and not participate in the same network. In America blacks and whites often lived on the same piece of land; blacks worked in the homes of whites. The physical distance was minimal, but the great social distance led to different varieties of American English.
Contact between languages lead to variations and changes. Situations of language contact are usually socially complex, making them of interest to sociolinguists. When speakers of different languages come together, the results are determined in large part by the economic and political power of the speakers of each language. In the United States, English became the popular language from coast to coast, largely replacing colonial French and Spanish and the languages of Native Americans. In the Caribbean and perhaps in British North America where slavery was practiced, Africans learned the English of their masters as best they could, creating a language for immediate and limited communication called a pidgin. When Africans forgot or were forbidden to use their African languages to communicate with one another, they developed their English pidgin into their native tongue. A language that develops from a pidgin into a native language is called a creole. African American Vernacular English may have developed this way.
Bilingualism is another response to language contact. In the United States, large numbers of non-English speaking immigrants arrived in the late 19th and early 20th century. Typically, their children were bilingual and their grandchildren were monolingual speakers of English. When the two languages are not kept separate in function, speakers can intersperse phrases from one into the other, which is called code switching. Speakers may also develop a dialect of one language that is heavily influenced by features of the other language, such as the contemporary American dialect Chicano English.