The method employed (used) in studying the history of the English language is called a method of Comparative Linguistics. This scientific means came into existence in the first half of the 19th century and proved to be of great use to the development of General Linguistics. Besides it gave birth to the History of separate languages as a science.

In the first half of the 19th century European linguists began to compare ancient and modern European languages: Latin, Greek, German, French, English, Lithuanian, Russian and others. However, nothing could be proved about their origin and relation until Sanskrit was discovered, studied and described. Only then it was proved that these languages are related. It appeared that some languages have common lexicological elements (roots of words), common features in their grammatical system and definite sound laws.

In the Indo-European languages the subject of the sentence is usually in the nominative case and that is why they are called Nominatival languages. The system of the numeral as well as that of the pronoun is very much alike. Many words are formed from the same roots such as MOTHER, die MUTTER, MATL, МАТЬ. The Method of Comparative Linguistics implies that languages do not develop uniformly. The development of the vocabulary, grammar and sound system is sometimes slower, sometimes faster. There are periods in the history of every language, when it undergoes many changes in all its aspects. But there are periods when the changes are slow and few.

English people do not understand German now without studying their language, while in ancient times the Germanic tribes understood each other.

However the Method of Comparative Linguistics is not a general one. It can be of use only when there are written documents. It cannot be applied to all languages in the same way. It came to life and developed as a method of studying Indo-European languages, i.e. inflective languages and so is not applied to non-inflective languages. So it is far from being universal.

Anyhow the importance of this method is great. The development of it may give the people an opportunity to classify the languages spoken on our planet. The discovery of kinship of the Indo-European family of languages was also of great importance.
Now about 2500 languages are spoken in the world. They may be classified according to their descent and kinship, for example. This classification is called the Genealogical classification. According to it languages are divided into 'families'.

A family consists of languages that developed from the tribal dialects of an ancient people. Having lost touch with each other those dialects developed into separate languages of the same family. The classification of languages based on the morphological structure of the word is called the Morphological classification.