In Early ME ben plus Part. I fell into disuse; it occurs occasionally in some dialectal areas: in Kent and in the North, but not in the Midlands. In Late ME it extended to other dialects and its frequency grew again, e.g.
Syngynge he was or floytynge al the day. (Chaucer) ('He was singing or playing the flute all day long.') The flod is into the greet see rennende. (Gower) ('The river runs into the great sea.')
At that stage the construction did not differ from the simple verb form in meaning and was used as its synonym, mainly for emphasis and vividness of description. Cf.:
We holden on to the Cristen feyth and are byleving in Jhesu Cryste. (Caxton)
('We hold to the Christian faith and believe (lit. "are believing") in Jesus Christ.')
In the 15th and 16th c. be plus Part. I was often confused with a synonymous phrase – be plus the preposition on (or its reduced form a) plus a verbal noun. By that time the Pres. Part. and the verbal noun had lost their formal differences: the Part. I was built with the help of -ing and the verbal noun had the word-building suffix -ing, which had ousted the equivalent OE suffix -ung.
She wyst not... whether she was a-wakyng or a-slepe. (Caxton) ('She did not know whether she was awake (was on waking) or asleep.') A Knyght ... had been on huntynge. (Malory) ('A knight had been hunting (lit. "on hunting").'
The prepositional phrase indicated a process, taking place at a certain period of time. It is believed that the meaning of process or an action of limited duration – which the Cont. forms acquired in Early NE – may have come from the prepositional phrase. Yet even in the 17th c. the semantic difference between the Cont. and non-Cont. forms is not always apparent, e.g.: The Earl of Wesmoreland, seven thousand strong, is marching hitherwards. (Sh)
What, my dear lady Disdain! Are you yet living? (Sh). Here the Cont. makes the statement more emotional, forceful.)
The non-Cont., simple form can indicate an action in progress which takes place before the eyes of the speaker (nowadays this use is typical of the Cont. form):
Enter Hamlet reading... Po1onius. What do you read, my lord?
It was not until the 18th c. that the Cont. forms acquired a specific meaning of their own; to use modern definitions, that of incomplete concrete process of limited duration. Only at that stage the Cont. and non-Cont. made up a new grammatical category – Aspect. The meaning of non-Cont. – Indef. – forms became more restricted, though the contrast was never as sharp as in the other categories: in some contexts the forms have remained synonymous and are even interchangeable to this day.
By that time the formal pattern of the Cont. as an analytical form was firmly established. The Cont. forms were used in all genres and dialects and could be built both from non-terminative verbs, as in OE, and from terminative verbs. They had extended to many parts of the verb system, being combined with other forms. Thus the Future Cont. is attested in the Northern texts since the end of the 13th c.; the first unambiguous instances of the Pert. Cont. are recorded in Late ME.
For many hundred years the Cont. forms were not used in the Pass. Voice. In Late ME the Active Voice of the Cont. form was sometimes used with a passive meaning:
My mighte and my mayne es all marrande. (York plays) ('My might and my power are all being destroyed.') (lit. "is destroying").
The Active form of the Cont. aspect was employed in the passive meaning until the 19th c. The earliest written evidence of the Pass. Cont. is found in a private letter of the 18th c.: ... a fellow whose uppermost upper grinder is being torn out by the roots...
The new Pass. form aroused the protest of many scholars. Samuel Johnson, the great lexicographer, called it a "vicious" expression and recommended the active form as a better way of expressing the passive meaning. He thought that phrases like the book is now printing; the brass is forging had developed from the book is a-printing; the brass is a-forging; which meant 'is in the process of forging', and therefore possessed the meaning of the Pass. Even in the late 19th c. it was claimed that the house is being built was a clumsy construction which should be replaced by the house is building. But in spite of all these protests the Pass. Voice of the Cont. aspect continued to be used and eventually was recognised as correct.
The growth of the Cont. forms in the last two centuries is evidenced not only by its spread in the verb paradigm – the development of the Pass. forms in the Cont. Aspect – but also by its growing frequency and the loosening of lexical constraints. In the 19th and 20th c. the Cont. forms occur with verbs of diverse lexical meaning.
The uneven development of the Cont. forms, their temporary regress and recent progress, as well as multiple dialectal and lexical restrictions gave rise to numerous hypotheses about their origin and growth.
Some scholars attribute the appearance of the Cont. forms in English to foreign influence: Latin, French or Celtic. These theories, however, are not confirmed by facts.
Numerous instances of OE beon + Part. I were found in original OE texts, particularly in the Anglo-Saxon Chronicals. But the construction is rare in translations from Latin, for instance in Wyklif's translation of the Bible.