Is he a teacher? Yes he is. Can you swim? No, I can’t. Have they got a car? Yes they have.
To form yes/no questions where there is an auxiliary verb or a modal verb, we invert the word order of a positive sentence. (He is a teacher > Is he a teacher?)
Do you eat fish? No I don’t. Does she know you. Yes she does.
When there is no auxiliary verb we use ‘do’ to form the question.
With question words
The same rules apply when there is a question word (‘what’, ‘where’, ‘when’, ‘why’, ‘who’, ‘which’, ‘how’, ‘how much’, ‘how many’)
Where is the hotel? What can you smell? Who has just arrived?
Where there is an auxiliary or modal verb, that verb is used to form the question.
How did you get here? When do your parents get back? How much does it cost?
Where there is no auxiliary verb, we use do.
Sometimes you might see questions like this.
Who broke the window? What happened next? Who told you that?
There is no auxiliary verb and the word order is not inverted.
These are called subject questions – because the question word is the subject of the sentence.
Look at these two questions.
Who does Romeo love? Romeo loves Juliet. Who loves Romeo? Juliet loves Romeo.
In the first question, Romeo is the subject of the verb.
In the second question ‘who’ is the subject and Romeo is the object.