Linguistics explores the structure of language, its uses and applications in society, connecting theoretical, descriptive and applied studies which address problems and issues in human communication. Courses in the structure of language examine its sounds (phonetics and phonology), words (morphology), sentences (syntax) and meaning (semantics), and the complex interactions between these properties. Students also study the way languages change across time (historical linguistics) and how different regional, social or occupational varieties develop (sociolinguistics).