Sociolinguistics studies dialect – any regional, social or ethnic variety of a language.
Variation in language is not helter-skelter. It is systematic. For instance, a speaker may sometimes pronounce the word mind to sound just like mine through a process called consonant cluster reduction. Pronunciation of the final –nd consonant cluster as –n tends to occur before consonants; i.e., the speaker’s choice of saying mine instead of mind is conditioned by a feature of the language itself (whether or not a consonant sound follows the word).For instance, a speaker is likely to say “I wouldn’t mind owning a BMW” (with both n and d pronounced before o), but “I wouldn’t mine borrowing your BMW” (with nd reduced to n before b).
Variation also correlates with social factors outside of language. For example, Appalachian working-class speakers reduce consonant clusters more often than northern Anglo-American working class speakers and working-class African Americans, regardless of their region, reduce consonant clusters more frequently than do other working-class speakers. Thus, the occurrence of final consonant cluster reduction is conditioned internally by its position in the speech stream and externally by the social factors of socioeconomic class and ethnicity.
Another example of an internal linguistic variable is the pronunciation of the words spelled pen, ten and Ben so that they sound as if they were spelled pin, tin and bin. This variable correlates with being Southern, regardless of age, gender, socio-economic class or ethnicity. However, among Southerners, the pronunciation of ask as if it were spelled ax correlates with ethnicity, because the pronunciation is used most often (but not exclusively) by African Americans.
Another pronunciation variant that correlates with a social category is heard in New Orleans. In working-class neighborhoods, words spelled with oi are often pronounced as if spelled er. For these speakers, then, the word point rhymes with weren’t. Age is another social variable. In North Carolina, elderly speakers often pronounce duke, stupid and newspaper with a y-sound before the vowel. Instead of the common pronunciations dook, stoopid, and nooz for these words, they say dyuke, styupid, and nyuz. (This is basically the difference all English speakers make between the words food and feud; feud has a y-sound before the vowel.) Speakers born after World War II seldom use this pronunciation.
The examples above have all concerned pronunciation, but language also varies in vocabulary, grammar and use.