As an illustration of the linguistic variation encountered in all nations, consider the contemporary United States. Ethnic diversity is revealed by the fact that millions of Americans learn first languages other than English. Spanish is the most common. Most of those people eventually become bilinguals, adding English as a second language.
In many multilingual (including colonized) nations, people use two languages on different occasions—one in the home, for example, and the other on the job or in public.
Whether bilingual or not, we all vary our speech in different contexts; we engage in style shifts. In certain parts of Europe, people regularly switch dialects. This phenomenon, known as diglossia, applies to “high” and “low” variants of the same language, for example, in German and Flemish (spoken in Belgium). People employ the high variant at universities and in writing, professions, and the mass media. They use the low variant for ordinary conversation with family members and friends.
Just as social situations influence our speech, so do geographical, cultural, and socioeconomic differences. Many dialects coexist in the United States with Standard (American) English (SE). SE itself is a dialect that differs, say, from “BBC English,” which is the preferred dialect in Great Britain. Different dialects are equally effective as systems of communication, which is language’s main job. Our tendency to think of particular dialects as cruder or more sophisticated than others is a social rather than a linguistic judgment. We rank certain speech patterns as better or worse because we recognize that they are used by groups that we also rank. People who say dese, dem, and dere instead of these, them, and there communicate perfectly well with anyone who recognizes that the d sound systematically replaces the th sound in their speech.
However, this form of speech has become an indicator of low social rank. We call it, like the use of ain’t, “uneducated speech.” The use of dem, dese, and dere is one of many phonological differences that Americans recognize and look down on.