"Do let us know" I know the meaning of let us know but what is the meaning of the sentence when "do" is used before let us know.
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
This is called an "emphatic do". I see there has been at least one question before on ELU but the answer did not mention the use in the imperative.
The auxiliary do can be used to add emphasis to an affirmative sentence when no other auxiliary is used in the sentence.
I do know what you mean.
I did tell him.
Do let us know what you decide.
Normal imperative → Let us know!
Adding emphasis → Do let us know!
"Do let us know!" can be used to show you are interested in what happens next. Here it can be a polite use, but in other contexts it can help stress different feelings (Mum to child, showing anger: "Do be quiet!").
Note that in speech "emphatic do" is stressed.
If an auxiliary is already present in the affirmative sentence, then this auxiliary is used for emphasis.
Adding of extra 'do' shows enforcement in speech.
"Let us know." means - okay, fine, let us know, it's no big deal.
"Do let us know" means- please, really let us know, we really need to know it.
Like, if you say "I went there and saw nothing", then in this sentence you simply went there and saw nothing.
Now in the reply to your sentence if someone asks- "You really went there or are you lying?"
Then to show your assurance that you really went there you will say forcibly - "Yes, I 'did' go there and saw nothing!"
If you just say- "Yes, I go there and saw nothing" then this sentence looks so plain. But adding an extra 'did' shows assurance that you really did the thing.