A noun clause is a group of words that serves as a subject or an object of a verb or as an object of a preposition.  It is composed of a marker, a subject, and a verb.

Examples:

Why she was late was not important.  [noun clause subject]
I don’t believe that we’ve met.  [noun clause object]
People judge others by what they do.  [noun clause object of a preposition]

If a noun clauses comes from a statement, it uses the marker that.

Examples:

The world is round.  (statement)
They don’t believe that the world is round.  (noun clause object)

NOTE:  You can drop the marker that when the noun clause is an object.
They don’t believe the world is round.  (noun clause object)

NOTE:  You cannot drop that when the noun clause is a subject.
That the world is round is a fact.  (noun clause subject)

More examples:

I knew that she had forgotten your name.   (noun clause object)
He told me that you were going to be late.  (noun clause object)
That his parents are divorced is well known.  (noun clause subject)

If a noun clause comes from an information question, it uses the marker that is the same question word as in the question: who, what, where, when, why, and how.

NOTE:  There is no inversion of the subject and verb.

Examples:

Who is she?  (information question)

• there is an inversion of the verb (she) and the subject (she))
I don’t know who she is.  (noun clause object)
• there is no inversion. The subject (she) is before the verb (is.))

What did she say?  (information question)
What she said is a lie.  (noun clause subject)

Where do they live?  (information question)
Could you please tell me where they live.  (noun clause object)

When does the game start?  (information question)
They can’t remember when the game starts.  (noun clause object)

Why didn’t he call me?  (information question)
Why he didn’t call me is not important.  (noun clause subject)

How will I know?  (information question)
How I’ll know is by reading the article.  (noun clause subject)

If a noun clause comes from a yes/no question, it uses the marker if.  It can also use the marker whether, but whether is more commonly used with or not.  Sometimes if is also used with or not, but never together.

Examples:

Do they need any help?  (yes/no question)
I wonder if they need any help.
I wonder if they need any help or not.
I wonder whether they need any help.
I wonder whether or not they need any help.
I wonder whether they need any help or not.

WRONG:  I wonder if or not they need any help.
(or not cannot be used right after if)

Only whether can be used if the noun clause is a subject

Examples:

Whether we’re having a picnic depends on the weather.
Whether or not we’re having a picnic depends on the weather.
Whether we’re having a picnic or not depends on the weather.

Whether it will rain tomorrow is anybody’s guess.
Whether or not it will rain tomorrow is anybody’s guess.
Whether it will rain tomorrow or not is anybody’s guess.

More examples:

We’re not sure if they will be able to help.
We’re not sure if they will be able to help or not.
We’re not sure whether they will be able to help.
We’re not sure whether or not they will be able to help.
We’re not sure whether they will be able to help or not.

I’d like to know if there is something good on TV tonight.
I’d like to know if there is something good on TV tonight or not.
I’d like to know whether there is something good on TV tonight.
I’d like to know whether or not there is something good on TV tonight.
I’d like to know whether there is something good on TV tonight or not.

To review:

Noun clauses that come from statements use the marker that.

Noun clauses that come from information questions use the markers: who, what, where, when, why and how.

Noun clauses that come from yes/no questions use the markers if and whether (or not).

Study this page and when you think you’re ready, do the following exercise.