I know I can use a subordinate clause as an object of a sentence.

I don't know who is that person.

Can I put this object at the beginning of that sentence

who is that person, I don't know.

  • No, you can't use a subordinate clause as an object. Your sentences are both ungrammatical. I suggest you need "I don't know who that person is", or the rather odd "Who that person is, I don't know".
    – BillJ
    Commented Feb 22, 2019 at 14:21

2 Answers 2


A poem we all learn in high school is "Stopping by Woods on a Snowy Evening," by Robert Frost. It begins:

Whose woods these are I think I know. 

It's a simple and legitimate inversion of "I think I know whose woods these are." In common speech, such inversions are used for emphasis:

Whether she's coming I can tell you, but what she'll be wearing is still a secret.

The comma is usually unnecessary. In your sample case, I suggest "Who that person is I don't know." It's an indirect question, so the interrogatory form "who is" is not correct.


Both I don't know and I don't know X work as full sentences. For that reason in

Who is that person, I don't know

there is no indication that know has a predicate. So, it sounds like two separate sentences, the first a question and the second an answer.

One way to integrate them in that order into a single sentence could be

Who is that person, is what I don't know.

In this one is, the second one, replaced know as the main verb. The subject is also no longer I, but it became Who is that person.

  • thanks for your reply. yea its true that these two sentences look different and are working differently.but if I write " what the task requires,he knows well". I think its working properly as object. what do you think Commented Feb 22, 2019 at 13:19
  • 1
    Your last sentence should be "Who that person is, I don't know", with subject-auxiliary inversion. "Who that person is" would then be a subordinate interrogative clause (embedded question).
    – BillJ
    Commented Feb 22, 2019 at 15:33

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