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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?

Hellion
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Alex
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    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. – 200_success Nov 06 '14 at 11:22
  • Closely related: [Do I have to use “do” in any “wh-” question?](http://ell.stackexchange.com/q/37902/1654) – apsillers Nov 06 '14 at 13:45
  • @200_ Well, and the form of the verb. – starsplusplus Nov 07 '14 at 00:01

2 Answers2

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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?
tunny
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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!

Araucaria - Not here any more.
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