1. "Whose birthday do you think IS IT?" or
  2. "Whose birthday do you think IT IS?"

I know that for questions the verb to be goes in front of the personal pronoun, however, why I have this strong feeling 2 is the correct one? Maybe both?


I think you are confused here by the fact that this sentence contains not just an interrogative main clause but also a subordinate "content" clause from which the complementizer that has been dropped. Only the main clause has subject/auxiliary inversion with do-support, not the subordinate clause.

Think about it from the point of view of the answer you expect. In its fullest form that would be something like this

 I  think [that] it is  X's  birthday.  

Note that there are two clauses here: the main clause is *I think [Y], and Y, the something that you think, is the subordinate clause [that] it is X's birthday.

Now let's walk through the steps you perform to turn this answer into your question.

 (1)                 I     think [that] it is  X's  birthday.  
 (2)                You    think [that] it is whose birthday.
 (3) Whose birthday you    think [that] it is
 (4) Whose birthday you do think [that] it is
 (5) Whose birthday do you think [that] it is?
  1. is the answer
  2. Replace the I with you, and replace the word which you are asking about, X's, with the appropriate interrogative term, whose:
  3. Move the interrogative term to the front; since it is not strictly a pronoun but a possessive modifying birthday it remains attached to the word it modifies and drags it along with it to the front.
  4. Since this is a question, you must invert the subject of the main clause (you) with the auxiliary verb. But there's no auxiliary in the original, so you add do to play this role. This is called do-support.
  5. Now you invert the auxiliary verb do with the subject; add a question mark and you're done.

The interrogative main clause now has the correct inversion, with do support. But the subordinate clause is not affected by this operation—it retains its original form, except that it has "lost" the element which you are asking about.

  • StoneyB you definitely are a perfect teacher. I always learn from your comprehensive answers. I feel happy that you are here to help:-)) – user33000 May 24 '16 at 8:47
  • Thank you very much Stoney B, your help is much appeciated. – claudio sepulveda May 24 '16 at 22:34

It is not both. Number two is the correct form here.

Whose birthday is it?

Is correct, but the question adds a second noun, and the verb we are asking about is think.

Whose birthday do you think it is

You can simplify the question if this one is too confusing, for example

What do you think it is?

This is also a more common, correct sentence, that displays the same behavior as the question you are asking about.


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