Historical linguistics is the study of not only the history of languages as the name implies but also the study of how languages change and how they are related to one another. The main job of historical linguists is to learn how languages are related to each other. The Important reason of why historical linguists study language change, that is because historical linguistics contributes significantly to linguistics and other sub area of linguistic theory. The major misconception about historical linguistics was that it was the study of the history of individual word or more properly said as ‘Etymology of individual words, but the kind of linguistic change that has undergone and the technique or method followed to recover their history. Lyle Campbell in his book ‘Historical Linguistics; an introduction (1998, page-5) says that the basic goal of historical linguists is not etymologies, but accurate entomologies an important product of historical linguistics work’. In the past many scholars had thought that the principle domain of historical linguistics was the study of ‘how’ languages change, believing that will answer to the question of ‘why’ the changes were too difficult to understand. However, since the 1960s, great studies have been done in understanding ‘why’ languages change. Today, we can say that historical linguistics are dedicated to the studies of ‘how’ and ‘why’ languages change, both to the methods of investigating linguistic change and to the theories designed