DO, DOES, DID + bare infinitive

The auxiliary verbs do, does and did are followed by the bare infinitive to form negative and interrogative sentences in the past simple and present simple tenses:

Do you take any vitamins?
He doesn't live here any more.
Did you ask the shop assistant?

Do, does and did can also be used in affirmative sentences to express emphasis:

I do know what you mean.
He does travel a lot.
I did want to write, but I forgot.