I don't understand structure of that sentence:

What happens to the cars produced in this factory?

Why not: What are the cars happen?

All what I saw are: what [do] ... or what [have] or what [be].

Why in this sentence 'happens' follows after 'what'?

  • This is a subject question in which "what" is used as the subject. You only need a do when what is used as an object. "What do you need? ". Note that you explicitly use what as an object if you reverse the wh-fronting. "You need what? " May 19, 2017 at 13:37
  • Perhaps my explanation is confusing. I'd rather you read this May 19, 2017 at 13:41
  • By the way, do you know what the question is asking? A possible answer to "What happens to the cars" would be "They are sold in Europe," not "They drive fast." The question is not asking what the cars do; it is asking what someone will do to the cars.
    – Chaim
    May 19, 2017 at 14:54
  • @user178049, I liked your answer most of all. I'll approve it if you write it. May 21, 2017 at 16:18
  • @user178049, I've found great example that helped me. "Who did Papa kiss?" vs "Who kissed Papa?" May 21, 2017 at 16:36

3 Answers 3


This is covered in Collins COBUILD English Grammar (Digital Edition) under the subtopic 5.22 Wh-word

When a wh-word is the subject of a verb, or when it forms part of the subject, the word order of the clause is the same as that of a clause in the declarative, i.e. the subject is put first, followed by the verb.

(Emphasis mine)

This is what happens here, the wh-word (what) is used as the subject in your sentence so it follows the same order in a declarative sentence.

However, you need a do-support (if there's no auxiliary) when the wh-word is used as an object of a preposition or verb.

What do you need?

The wh-word (what) is used as object of the verb need. It will be clearer if your undo the wh-fronting. Like this

You need what?


This pattern

What are the cars _________.

is a question form of the statement:

The cars are __________ what.

In that pattern, what is a direct object:

What are the cars burning? (that is, what kind of fuel?)

The cars are burning diesel fuel.

Since happen is an intransitive verb, it does not take a direct object. We cannot say:

The cars are happen what. ungrammatical

And since we cannot make that statement, neither can we ask the question

What are the cars happen? ungrammatical

To happen means 'to occur'. An event occurs. An action happens.

Accidents happen.

This car's door is dented! Something happened to the car.

The prepositional phrase to the car after happened expresses the idea "event occurred having an effect on the car".

Something happened which produced an effect on the car.

Something happened to the car.

What happened to the car?


I don't understand structure of that sentence:

What happens to the cars produced in this factory?

Why not: What are the cars happen?

For he/she/it in the simple present tense, add 's' in the verb. But there isn't 3rd person singular in your sentence.

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