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very often we see the description like this:

Many people realize that they didn't do any wrongdoings, so they cannot understand why they have to be punished. or ...., so they cannot understand why do they have to be punished.

or we ask "why do you fight?" can we omit the "do", say "why you fight?"

Thanks!!

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marked as duplicate by Armen Ծիրունյան, StoneyB, RegDwigнt May 18 '13 at 12:56

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Welcome to ELU, McGushin. Questions like this are generally considered too basic for this site, but are in many cases accepted on the English Language Learners site. You may click on 'flag' above and ask that the moderators migrate your question there. –  StoneyB May 18 '13 at 12:49

1 Answer 1

No, you may not omit the do.

A question headed by a Wh- interrogative (who, whom, whose, what, which, where, when, why, how, and a few others) must have a finite verb in the second position; and that verb must be either a form of be or an auxiliary verb.

indicative:       interrogative:   
He is right.      Why is he right?    ... the finite verb IS is a form of BE  
You must fight.   Why must you fight? ... the finite verb MUST is a modal auxiliary  

But if the finite verb in the clause is not one of these, then it must be replaced with a do construction (this is called 'DO-support').

indicative:       interrogative:   
You fight.       *Why fight you?      ... wrong: FIGHT is not an auxiliary
                 *Why you fight?      ... wrong: there is no verb in second place
                  Why do you fight?   ... right: DO is an auxiliary in second place.

A tricky piece is that do and have (and a few other verbs) may act as either an auxiliary or as an ordinary lexical verb. You must be careful to employ do in the second case:

indicative:       interrogative:   
They do wrong.   *Why do they wrong?      ... wrong: DO here is not an auxiliary
                  Why do they do wrong?   ... right: the first DO is an auxiliary
He has a car.    *Where has he a car?     ... wrong: HAS here is not an auxiliary (but
                                                 this was at one time acceptable)
                  Where does he have a car? . right: DO-support provides the auxiliary

Second must sometimes be loosely interpreted with which, what and whose; if used as adjectives these are followed by the NP they modify, as in What courses are you taking?
* before an utterance indicates that it is not ordinarily acceptable

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