Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Language change is the phenomenon whereby phonetic, morphological, semantic, syntactic, and other features of language vary over time. All languages are continually changing. At any given moment the English language, for example, has a huge variety within itself, and descriptive linguists call this variety synchronic variation. From these different forms comes the effect on language over time known as diachronic change. Two linguistic disciplines in particular concern themselves with studying language change: historical linguistics and sociolinguistics. Historical linguists examine how people in the past used language and seek to determine how subsequent languages derive from previous ones and relate to one another. Sociolinguists study the origins of language changes and want to explain how society and changes in society influence language.