Which of the following is correct please?

1- I don't know which one is you.
2- I don't know which one you are.

  • 5
    Context is essential. Here, both phrasings are legitimate, but there might be circumstances where one is preferred to the other. What is the situation where you are seeking to employ these phrases? What has a web search or other basic research on them shown? Please edit your post to include more details.
    – choster
    Jul 11, 2017 at 22:12

2 Answers 2



A relative clause (whether it's a free relative or bound relative or an embedded question) works just like a fill-in-the-blank question: the relativizer (that, or a wh- word, or a phrase involving a wh- word) always signals the presence of a 'gap' where a constituent has been omitted. Strip off the relativizer and the location of the gap is usually obvious:

... which one you arethere's no predicate complement to are, so that must be the gap:
you are ____

... which one is youthere's no subject to is, so that must be the gap:
→ ____ is you.

As Tᴚoɯɐuo suggests, the form of the verb BE makes it pretty clear which element is the subject.

But the use of the copular verb BE adds another wrinkle to your examples. In this case it doesn't matter which form you use. This is because your examples are specifying copular clauses, in which the predicate complement designates the identity of the subject: the subject and the predicate complement are the same entity. Just as in mathematics, if P=Q then Q=P, so the clause is reversible:

That one is you = You are that one, and
which one is you = which one you are

This would not be the case if these were ascriptive copular clauses, in which the predicate complement is a quality or category of the subject. A subject is not the same thing as its qualities, so the clause is not reversible.

You are tall, *Tall is you, and
how tall you are *how tall is you

  • +1, So both are correct and equal, yes?
    – Abbasi
    Jul 12, 2017 at 11:03
  • @Abbasi In this particular case, yes. Jul 12, 2017 at 14:21

That is a great question.

I don't know

... which one you are

... which one is you.

If, in the which-clause, one the subject, then the verb is third-person singular and you is the predicate complement.

... which one is you.

If, in the which-clause, you is the subject, then the verb is second-person singular (with "one", plural with "ones") and one is the predicate complement, with inversion of normal subject-verb order. The complement of are appears first.

I need to use my life-line to @Araucaria or @StoneyB to get an explanation for why this happens.

  • I had to look long and hard at this one to convince myself that it is not Jesperson's prop-word "one". I gave up. I don't know which one it is. What's more, I don't know which one is it. Jul 11, 2017 at 22:42
  • There's no inversion ... I've tossed you a lifeline. Jul 12, 2017 at 0:28
  • I'll wager that StoneyB has never watched Who Wants To Be A Grammarian?. Jul 12, 2017 at 1:23
  • @StoneyB: Thanks for clearing that up. I wasn't taking which-one as a unit. Jul 12, 2017 at 11:01

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