"what did Diane say?" vs "what Diane said?"

Question

what did Diane say?

what Diane said?

How do you understand which one is correct? The book that i study myself says if question words(who/what) is subject of the sentence do/did is omitted. My problem is that i can not understand if its subject or object of the sentence.

another example:

Who lives here?

Who does live here?

To me, both sounds correct. So my question: is there a way to find the correct form without looking subjects or objects of the sentence. and does native speakers find the correct form like i do? Thanks

Answer 1

1) How do you understand which one is correct?

You should identify the subject and object. It would be very unusual for "Diane" to be the object of the verb "say", so we can assume that it is instead the subject. In that case, "what" is the object, so we need an auxiliary verb:

What did Diane say?

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2) is there a way to find the correct form without looking subjects or objects of the sentence.

In general, you should identify subjects and objects to be sure that you are structuring clauses correctly. However, sometimes other factors will determine the verb form. For example, in your last example ("Who lives here?" / "Who does live here?"), both versions are grammatically correct and the auxiliary verb is used for emphasis.

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3) does native speakers find the correct form like i do?

How you find the correct form is unclear. The book that you're using might not be very accurate. (As I mentioned, the auxiliary verb "to do" is possible even when the subject is a wh-word.)

Answer 2

Correct: What did Diane say? (What-object, Diane-subject) [ Incorrect: what Diane said? ]

Correct: Who lives here? (Who-subject) [ Incorrect: Who does live here? ]

He lives here.(subject-He)

Who lives here? (subject-Who)

What happens? What happened? (What-subject)

What do you want? What do you say? (What-object, you-subject)

Who saw you? (Who-subject)

Who did you see? (Who-object, you-subject)

[ What did Diane say? Tell me what Diane said. Do you know what Diane said? I don't know what Diane said. ]