1.1.Historical linguistics was launched in the nineteenth century by comparing and correlating sound changes in Indo-European languages as a way of identifying which languages belong to that family.Very quickly interest expanded to the cataloguing of lexical, morphological, syntactic and semantic change in Indo-European and other language families.All languages and all varieties of every language constitute potential data for linguistic research, as do the relationships between them and the relations and structures of their components.A linguist is someone who studies and describes the structure and composition of language and/or languages in a methodical and rigorous manner.Comparative studies of language contact and genetic relationship have led to well accepted descriptions of relations among different languages and their grouping into families.Linguistics is the study of the human ability to produce and interpret language in speaking, writing and signing (for the deaf).What is Linguistics?1.1.1.