People say:

"How old do you think I am?"


"Do you know how old I am?"

I am wondering:

  1. What's the reason causing the different location of how old between the two questions?

  2. Can we say

"Do you think how old I am?"


"How old do you know I am?"

If we can't, what is the reason?

  • Added the question: "How old do you know I am?" – Jun Apr 30 '20 at 9:40

It might be helpful to note it's not just the location of these two words; they have completely different structure. The first question consists of a single clause. The second has 2 clauses.

Also, the type of answer elicited is different. For "How old do you think I am?" the answer is a number. On the other hand, "Do you know how old I am" is a yes/no question. The statement in (2) would also be a yes/no question, perhaps equivalent of "do you have a guess as to how old I am?"

  • Thank you. Do you mean > On the other hand, "Do you think how old I am"? – Jun Apr 29 '20 at 23:09

The reason for the particular order you have to follow is that questions are formed according to the type they belong to.

The questions below are wh-questions (ref.).

  1. with an auxiliary


  1. without any auxiliary (when WH-words replace subjects already)


How old           do you think I am?
Where               do you think they went?
What road      do you think they followed?
When                do you think it'll rain?
How                  do you think we should do?
Who                  do you think told them?

The question below are yes-no questions (ref); they are formed differently.

Yes / No questions are the questions which are answered yes or no. It means when we are asking yes/no questions, we are expecting the answer, yes or no.

To form Yes/No questions, we use one of these verbs: auxiliary verbs ( be, do and have ) or modal verbs ( can, may,etc.).

We can not use questions words like what, how, why, who, etc. whilw making Yes/No questions.

Do         you know how old I am?
Can       you tell where they went?
Will      you know what road they followed? …


Generally, when you form a question in English, you perform three processes:

  1. If the main verb is neither an auxiliary verb nor a form of "to be", then replace the main verb with a conjugated form of "do" followed by a bare infinitive.
  2. Put the main verb before the subject.
  3. Pull the question word to the beginning of the question.

However, process 2 is generally only done in direct questions—questions that you are asking someone as a complete sentence which stands alone. In indirect questions—questions are used as pieces of another sentence—process 2 is not performed.

The question "How old do you think I am?" is a direct question where processes 2 and 3 are applied. So first we have the question word (which is actually two words, "how old"), then the main verb, then the subject.

The question "Do you know how old I am?" is a yes-or-no question which contains an indirect question as a subordinate clause. That indirect question is "how old I am". Since it's an indirect question, process 2 is not applied. And since the entire question "Do you know how old I am?" is a yes-or-no question, it has no question word and process 3 is not applied.

"Do you think how old I am?" sounds like nonsense. The question word is "how old", and it should have been put at the beginning of the question in order for the question to make sense.

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