"Who wrote ... ?" or "Who did write ... ?" [duplicate]

Possible Duplicate:
Why is there no form of “do” in questions of the type “who knows?”

I want to know which is the correct way to ask this question:

Who wrote this song?

or

Who did write this song?

If the first one is the correct one, why doesn't it have an auxiliary? Which rule does it follow?

Solution 1:

You only need "do" support when there's inversion. So if the WH-word/phrase is the subject of the question (and so there's no inversion), then you don't need "do":

What happened?

Which computer calculates faster?

On the other hand, if the WH phrase is the object (and there is inversion) then you need "do":

What did you drink with your meal?

Which computer did you buy?

Alternatively, if there's already an auxiliary verb (including a modal), you don't need add another one with inversion (and indeed, inversion or not, you can't usually use "do" alongside another modal/auxiliary):

Which computer can I buy?

When will you finish by?

An exception that can occur, in questions just like in ordinary statements, is that the auxiliary "do" can be used to mark a contrast. For example:

Speaker A: Mr Scarface didn't steal the car.

Speaker B: Well who did steal the car, then?

Another exception is so-called in situ questions, where you ask a question for confirmation/out of surprise, and where there's no inversion even though ordinarily there would have been. In this case, again because there's no inversion, you don't use do support:

You bought which computer? (implies: "I'm surprised you bought that computer!", or "please confirm again which computer you bought because I didn't hear you properly")

Solution 2:

Both are potentially correct, depending on context. The first is the simple past -- it's the most basic form of the past tense. "Wrote" is the past tense of "write." The second might be said in response to a negation, with emphasis on did:

"John didn't write this song."

"Who did write this song?"

Did can also be used in interrogative forms with more specific pronouns or nouns than "who." As in:

"Did Paul write this song? Or did you write it?"