According to English scientists Henry Sweet classified this periods are connected with the development of English endings. Henry Sweet classified them as
1. The Period of Full Endings,
2. The Period of Levelled Endings in reality contains the levelled vowel in the ending, but at the same time lots of endings were already lost;
3. The Period of Lost Endings – present-day language, as we know, is not totally devoid of endings, for some of the paradigmatic forms are still made by means of endings, scarce as they are.
There is a tradition of recognizing
1. The Old English period (449-1066), Early Old English may be taken separately, as the period of pre-written functioning of the language. The formation of kingdoms on the British territory transformed the tribal dialects into regional (local) dialects that took place during the later, Written Old English (or Anglo-Saxon period).
2. The Middle Eglish (1066-1475), the Early Middle English the writings of the period, represented mainly by the Anglo-Saxon Chronicle, Peterborough Chronicle, such poems as Ormulum. Late Middle English which came to our times in writings of G. Chaucer already presents a paragon of speech. London dialect becomes more and more prestigious, and what is written in «The Canterbury Tales» is already almost understood by a reader without a special linguistic training.
3. New English 15th century. Early New English – known as Shakespeare;s English is represented by numerous writings of a whole bunch of prominent thinkers, writers, scientists. Late New English is established and reviewed, and that is what you are studying in the course of practical English.