Study materials
These two questions differ by one word inside, and they have to be answered in different ways.
Do you know what he wants?
What do you think he wants?
Notice where the question word has moved. With know it stays inside; with think it comes right to the front. That is not stylistics but two different kinds of question.
Why think pulls the question word forward
The verbs think, believe, suppose, guess, imagine and expect do not ask about a fact. They ask for your opinion, so the question stays open and needs a full answer.
Where do you think she went?
Who do you believe wrote it?
Know, remember, wonder and be sure do the opposite: they close the question, and a yes or a no will do. So the question word stays inside where it was.
Do you know where she went?
The word order inside is the same in both cases: subject before verb, with no helper do.
Whether or if
In most places they are interchangeable, but whether has a wider range. There are three positions where if does not work.
| Position | What is allowed | Example |
|---|---|---|
| after a verb | both | I wonder whether it works. |
| after a preposition | whether only | It depends on whether he agrees. |
| before an infinitive | whether only | I don't know whether to call. |
| as a subject | whether only | Whether he agrees is unclear. |
The phrase whether ... or not expresses complete indifference to the answer, and or not can go in two places.
Let me know whether or not you can come.
Let me know whether you can come or not.
A question with no subject
When you are asking not about a fact but about a choice of action, a plain infinitive can follow the question word. The result is short and impersonal.
I don't know what to say.
She asked me where to park.
We're deciding whether to accept.
This works only where the doer is clear from context. With why it is not used at all.
Full stop or question mark
The mark at the end depends not on the embedded clause but on whether the opening of the sentence is a question.
Could you tell me where the station is?
I wonder where the station is.
I'd like to know when the report is due.
The mistakes everyone makes
The first is leaving the question word inside after think.
Do you think what he wants? → What do you think he wants?
The second is inverting twice.
What do you think does he want? → What do you think he wants?
The third is taking if after a preposition.
It depends on if he agrees. → It depends on whether he agrees.
All three are caught by two questions. Can this be answered with a yes or a no? And has question word order already been used at the front of the sentence?
Try it right now
Build three English questions about one person: one with do you know, one with what do you think, and one with whether to.
Then rewrite the first with I wonder and check which mark belongs at the end.