Study materials
Take two ordinary statements and turn them into questions. You will see the mechanism differs.
She is at home. → Is she at home?
She works here. → Does she work here?
In the first sentence the verb itself moved forward. In the second the verb cannot do that, so a helper had to be called in. That is the whole system.
What moves to the front
Verbs fall into two groups. Some manage on their own; the rest need do.
| Statement | What moves forward | Question |
|---|---|---|
| she is ready | the form of be | Is she ready? |
| she can swim | can itself | Can she swim? |
| she works | the helper do or does | Does she work? |
The rule is simple: if the sentence already holds be or a modal, that is what moves. If it holds an ordinary verb, do arrives.
The question word comes first
A wh-question is built on top of a yes-no question. The question word simply goes in front of it, and nothing else changes.
Where do you live?
Why is he sad?
What does Mia want?
There are not many of these words: what for a thing, where for a place, when for a time, who for a person, why for a reason, how for a manner.
A special case: who as the subject
Here the order breaks, and not by accident. If who is the one performing the action, no helper is needed: there is nothing to move.
Who lives here?
Who do you visit?
The check takes a second. Try answering the question. If the answer lands in the subject slot, do is not wanted.
The short answer repeats the helper
When answering, English does not repeat the whole sentence. The word that moved forward is enough.
Is she ready? Yes, she is.
Do you like tea? Yes, I do.
Can he swim? No, he can't.
The mistakes everyone makes
The first is building a question with statement order.
Where she works? → Where does she work?
The second is keeping the ending after does.
Does he plays? → Does he play?
The third is adding do to a question where who is the subject.
Who does live here? → Who lives here?
All three are caught by one glance at the sentence. What in it can move forward? If be or a modal is there, that is the one. If not, it is do. And if the question is about the subject itself, nothing moves at all.
Try it right now
Make three questions for one person: one with be, one with an ordinary verb, and one with a question word.
Then add a fourth starting with Who that asks about the doer. If no do appeared in it, the topic is done.