“Where is the dog?”
“Can you tell me where the dog is?”
Both of these questions ask the same thing, but they are different kinds of questions. “Where is the dog?” is called a direct question and “Can you tell me where the dog is?” is an indirect question even though both questions are asking the same thing. The difference is that the second question is longer and has a more polite way of asking the question, which is the main difference between indirect and direct questions.
Indirect questions use a form of the verb “to do”, such as “Do you know where the dog is?” Some of these questions are not really questions and more like statements, such as “I wonder what I will have for dinner.” One definition of this kind of question is that it is a polite way of encouraging a response from someone.
It is important to realize that indirect questions do not use the verb form of “to do” in the main question. Let’s use a direct question “when does the store open?” as an example. The indirect version of this would be “can you tell me when the store opens?”. An incorrect version of an indirect form would be to say “can you tell me when does the store open?” Notice how using the verb form of “to do” (does) is not to be used in the main question of the indirect form.
There are many ways to create an indirect question. Remember, not all indirect questions possess a similar sentence structure as a normal question. In other words, indirect questions can be a way of asking something without needing a question mark at the end of the sentence.
For example: I’d be curious to know how much gas costs today.
That is an indirect question in the sense that it encourages a response from the listener but is not formally structured as a question.
Here are some of the endless ways to start an indirect question:
I wonder if…
It’d be interesting to know…
I can imagine that was…
I can’t remember whether or not…
I wish I knew…
You can combine these phrases with any direct question to form an indirect question.
Here are five direct questions:
Is Jim going to the game?
How far can that plane fly?
Was that experience terrifying?
Did I close the garage?
When will you be returning home?
Let’s combine the five ways we listed of how to start an indirect question with the five direct questions listed above.
I wonder if Jim is going to the game.
It’d be interesting to know how far that plane can fly.
I can imagine that was a terrifying experience.
I can’t remember whether or not I closed the garage.
I wish I knew when you will be returning home.
Notice how all of the direct questions ended in a question mark. Yet, by using indirect question phrases, we transformed all of those questions into a sentence that doesn’t use a question mark.But don't be confused. Plenty of indirect questions still need a question mark. One example of this is : Would you mind telling me what time it is?
Source : www.grammar.com