I have a dilemma. I know how to use this, but I'm trying to explain it to someone and I can't find a logical explanation.

So here it is:

  1. Who called last night?
  2. Who did you call last night?

Why does the second sentence contain "did" when the first one doesn’t?

  • 2
    The second sentence is technically incorrect: it should be "Whom did you call last night?" However, many native English speakers confuse who and whom, and the intended meaning will be deduced from the word order rather than the case of the pronoun. Commented Nov 6, 2014 at 11:22
  • Closely related: Do I have to use “do” in any “wh-” question?
    – apsillers
    Commented Nov 6, 2014 at 13:45
  • @200_ Well, and the form of the verb. Commented Nov 7, 2014 at 0:01

2 Answers 2


Michael Swan explains this clearly in his Practical English Usage (2005.481).

When who, which, what or whose is the subject (or part of the subject), do is not normally used: Compare:

  • Who phoned? (Who is the subject.)
  • Who did you phone? (Who is the object.)

[...] But do can be used after a subject question word for emphasis, to insist on an answer:

  • Well, tell us - what did happen when your father found you?
  • This makes it pretty clear, but I have one more curiosity. What is the subject in your second example? Is it "you"?
    – Alex
    Commented Nov 6, 2014 at 11:48
  • @ Alex. Yes it is.
    – tunny
    Commented Nov 6, 2014 at 12:25

If the Wh- word represents the subject then we don't need to use do, and we don't need to change the subject and auxiliary verb.

However, It can be a bit difficult to understand if who/which is the subject. One way to find this information is to give a full answer to the question:

  • X called.
  • I called X.

If X is the subject of the answer, then it's usually the subject of the question, and we don't need do here. If it isn't the subject we need do:

  • Who called
  • Who did I call?

Hope this is helpful!

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