1

(1) I don't know what graph theory is.

According to the grammar, I believe it should be:

(2) I don't know what is graph theory.

But is it spoken colloquially the way I wrote it in (1)?


Grammar note:

We don't find subject-auxiliary inversion if the wh-word is the subject:

  • Who killed Cock Robin?
  • Who is coming to dinner?

We could assume the same is true for:

  • What is graph theory?

So it seems that we might assume that the embedded questions look like this:

  • I don't know who killed Cock Robin.

  • I don't know who is coming to dinner.

  • I don't know what is graph theory.

0

Your first example is correct:

I don't know what graph theory is.

It is wrong to say "I don't know what is graph theory.", although it is such a common mistake with non-native speakers that you will see it quite frequently.

In general I believe the order is reversed when the unknown is the object - in other words the verb and the known noun would be in the same order as they would in a statement. So:

Somebody killed Cock Robin

I don't know who killed Cock Robin.

The unknown is the subject so verb before noun.

Cock Robin killed somebody

I don't know who Cock Robin killed.

The unknown is the object, so noun before verb.

In your example:

Graph theory is something

I don't know what Graph theory is.

Noun before verb because the unknown is the object.

For your other examples:

Somebody is coming to dinner.

I don't know who is coming to dinner.

Verb before noun because the unknown is the subject.

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-1

This is correct.

https://www.collinsdictionary.com/dictionary/english/i-dont-know-how-what

Example #3 clearly states I don't know what .... is playing at.

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  • 2
    You say "this is correct" but you might want to clarify what "this" is referring to. – KillingTime Sep 19 '19 at 13:00

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