Sociolinguistics studies the use of language in social interaction, and the subject focuses on the use of language in the media, in corporations or in ordinary conversations. At the Ph.D. level, a sociolinguistics dissertation topic would likely span the intersection of linguistics and sociology, and a student may even be a member of both departments.

Race and Language

A student of sociolinguistics might focus on how a particular racial group uses a certain language. A famous and commonly studied example is African-American Vernacular English, known as both AAVE and Ebonics. Possible Ph.D. topics could focus more closely on the linguistic aspects of Ebonics, such as the tones, rhythms and sounds that distinguish AAVE from standard American English. Alternatively, students could focus on the social and economic impact of Ebonics in American society.

Social Class and Language

A commonly studied sociolinguistics topic is the intersection of language and social class. There are numerous examples within the English language where a person's social class impacts his style of speaking. In Britain, for example, the "Cockney" accent is famously the language of the urban working class in London, and so a student could study how and why the working classes uses this style of English. Within the United States, similar examples abound, and students could even focus narrowly on a single detail, like the class implications of using the word "ain't."

How Language Changes

Sociolinguistics does not by definition need to focus on the present. Students, for example, could focus on how the English language has changed over history. Students could choose to go back very far in history, and focus on the origins of English, and the Norman invasion of Britain's impact on language formation. In a topic like this, students might explore the relationship between English and French. Alternatively, students might instead focus on something contemporary, like gradual decline of the Boston accent in New England, or the causes of regional accent differences within the United States.

Teaching and Education of Language

Students hoping to focus on a more methodological project could focus on the teaching and education of a language. An interesting topic might be the different styles of learning English as a second language. Students could closely examine how certain cultural backgrounds affect a student's ease of learning a language, and why this is the case. Alternatively, students could analyze new ways of teaching the language more effectively to overcome hurdles that are common in ESL teaching.