Can “be” be used with the modal verb “do”?

Question

These two sentences are both valid

I write this sentence.

I do write this sentence.

Are these both valid?

I am writing this sentence.

I do be writing this sentence.

Answer 1

The rule of Do-Support applies to every main verb in English, except auxiliary verbs.

Do-Support is the process that provides the dummy auxiliary do to carry the tense and swap with the subject in Yes/No- and Wh-Questions

• Do you still love her?
• What do you love about her?

tag questions

• You still love her, don't you?

and negations

• You don't love her any more.

However, there are two important qualifications for this rule:

1. The verb be is always treated as an auxiliary verb, even if it's the only verb in its clause. I.e, it can never invoke Do-Support. Which is the answer to the OP's question. Other isomorphs of do can occur with be, however:

   • Do be a "Doo Bee", and don't be a "Dont Bee". - Emphatic do, active noun predicates.
   • What I'm gonna do is be her bodyguard. - Active do, active noun predicate.

2. The verb have, in its sense of "possess", may be treated

   • either as an auxiliary verb (i.e, commuting with the subject: Have you the time?)
   • or as a main verb (i.e, allowing Do-Support: Do you have the time?)

Answer 2

"I do be (something, something)....." is used regularly in everyday speech in South-East Ireland, where I grew up, but it is not regarded well, and a sign of being from a very specific type of rural, working class background. Its used in this context as a continuous present: "I do be always listening to that radio show on my way home from work"

Answer 3

What the second of the first pair is doing is adding emphasis. Because we normally use the auxiliary verb "do" in interrogative and negative sentences, not positive sentences.

Question: Do you like apples?

Positive sentence: You like apples.

Negative sentence: You don't like apples.

However, "do" is used in a positive sentence to add emphasis.

Ex.

I do believe in fairies, I do! I DO!

If my guess is right and you're trying to duplicate the act of emphasizing in the second pair, then it should be done this way:

First pair:

I write this sentence.

I do write this sentence.

Second pair:

I am writing this sentence.

I am writing this sentence.

As you can see, there is no need to add another auxiliary verb in the second pair because the word "be" or "am" is already one.

Answer 4

All except the last are grammatical, but the second would be found only infrequently. In some regional dialects the construction illustrated by I be writing this sentence is also found.