Q: “What are you doing?” *Q1: “What do you do?”
A: “I am making tea” *Q2: “I make tea”.
The English present continuous (using am/is/are + the “ing” form of a verb to indicate that the action is temporary, unfinished or ongoing) is less of an anomaly than ‘do’ [see We do use ‘do’ a lot in English, don’t we? Why do we do this? below]. It exists in a few other European languages (Icelandic, Dutch and Italian) although it is used less regularly and in different ways. In most of the other European languages the imperfective/continuous aspect is used only for past tenses and there would be no difference between the Q/*Q1 and A/*A1 forms above.
In South Asian languages (like Hindi or Tamil) the use of the present continuous is universal.
ham likh rahe hain
we – write – ing – are
We are writing
Speakers from countries such as India and Sri Lanka tend to overuse it in English because in their own languages it is used for both action and state verbs. In English it only applies to action verbs -except, of course, in McDonald’s slogans:
In the 14th century or thereabouts a new present continuous form emerged in Middle English modelled on a Brythonic/Welsh construction:
mae --- yn --- dysgu
be + preposition + verbal noun
He is learning
This was not simply the verbal noun/gerund found in other Germanic languages but clearly included the notion of imperfectivity (temporary, unfinished and ongoing action) which paralleled an existing Brythonic usage. British learners of English may have felt the need to distinguish between perfective and imperfective aspects and used this construction to do it.
The most common pattern was the -ing(e) form which spread from the southwest (in the Middle English period) where Celtic contact was strongest.
It looks as if the Old English –and(e)/-ing(e)/-ende/-inde gerund merged its use with a British present continuous form to create an all singing -all dancing present participle which is the modern English ‘-ing’ form.
Old English itself would probably have got no further than the Germanic gerund.