Do you know where it is/is it? – Word order in subordinate clauses in English

by Jakub Marian

Tip: See my list of the Most Common Mistakes in English. It will teach you how to avoid mis­takes with com­mas, pre­pos­i­tions, ir­reg­u­lar verbs, and much more.

Word order differs between questions and subordinate clauses (i.e. sentences beginning like “the place where …”, “the time when …”, “the man who …”). While word order in questions usually poses few problems, mistakes in subordinate clauses are very common.

Clauses beginning with “why”, “where”, “when”, etc., are often misleading because they look like questions (for example “Has she told you when …” or “I don’t know why …”). The rule here is that word order in subordinate clauses is exactly the same as in ordinary (non-question) sentences, that is:

I don’t know why someone does something.
I don’t know why someone is doing something.

(notice that “does” and “is doing” comes after “someone”). For example:

I don’t know why she did it. (correct)
I don’t know why did she do it. (wrong)
I don’t know why she has done it. (correct)
I don’t know why has she done it. (wrong)

The same would happen in a question:

Do you know why she did it? (correct)
Do you know why did she do it? (wrong)
Do you know why she is doing that?” (correct)
Do you know why is she doing that? (wrong)

But isn’t word order different in questions? Yes, but the question is “Do you know …?”. The part “why she did it” is a subordinate clause, no matter what comes before it. People tend to make mistakes especially after “who” and “what”:

Do you know who he is? (correct)
Do you know who is he? (wrong)

The structure is slightly different if there is no subject in the subordinate clause, i.e. when we actually ask about the subject:

Do you know who did it?
Since it has the same as the structure as the corresponding question, it shouldn’t pose any problems.

This article was based on my guide to the most common mistakes in English, which explains many similar topics. Why don’t you check it out?