Grammar · Clauses, Connectors & Sentence Style
Noun Clauses & Whether vs If
A whole clause can work like one noun. Learn to build these clauses, and when whether works but if doesn’t, with the film Inception.
Grammar › Clauses, Connectors & Sentence Style › Noun Clauses & Whether vs If
The rule in one sentenceTo put a yes/no question inside a longer sentence, use whether or if after verbs like ask, know and wonder, but only whether works at the start of a sentence, after a preposition, before to + verb or right before “or not”.
About the film
Inception is a 2010 science-fiction thriller written and directed by Christopher Nolan. Dom Cobb is a skilled thief who enters people’s dreams to steal their secrets. A powerful businessman called Saito asks Cobb if he can do the opposite and plant an idea in someone’s mind, and Cobb’s team must decide whether such a job is even possible.
What does it do?
A noun clause is a group of words with its own subject and verb that does the job of a single noun. Compare I know the answer with I know what the answer is: the second sentence puts a whole idea where one noun used to be. Noun clauses usually begin with that, a question word such as what or how, or whether / if.
When the hidden question is a yes/no question, you need whether or if. In everyday speech both are fine after verbs like ask, know, wonder and check. Whether sounds a little more formal, and it is the only choice in a few positions that if can’t fill.
In the first two tiles, either word would be correct. In the last two, only whether works: the third tile starts with the clause, and the fourth puts it after the preposition about and before to + verb. Notice too that the word order is normal: he will ever go home, not will he ever go home.
Ariadne asks if dreams can be controlled. (a simple object after ask: if is fine)
Ariadne thinks about whether to join the team. (after about and before to: only whether)
If you’re ever unsure, choose whether. It works in every position, while if only works in some.
Visual guide
Teacher Teddy’s illustrated guide to this rule is being drawn — the full swipe-through infographic will appear here soon.
How to make it
whether — works everywhere
Arthur wants to know whether the idea is possible.
Cobb doesn’t know whether Saito can be trusted.
don’t / doesn’t know whether …Have they decided whether to take the job?
Whether + to + verb: only whetherif — only after the verb
Saito wants to know if Cobb is the best.
Ariadne can’t tell if Cobb is serious.
can’t tell if … = can’t be sure if …Do you know if the team is ready?
Do you know if …? (polite and common)When to use each one
whether
if
Words that help: other noun clauses
Not every hidden question is a yes/no question. These words start other noun clauses.
that → a fact or an opinion
what / how / why → a hidden wh-question
Common mistakes
❌ If the plan will work is still unclear.
✅ Whether the plan will work is still unclear.
If can’t start a sentence as the subject. Use whether.
❌ They argued about if they should trust Saito.
✅ They argued about whether they should trust Saito.
After a preposition like about, only whether is possible.
❌ Ariadne can’t decide if to join them.
✅ Ariadne can’t decide whether to join them.
Before to + verb, always use whether.
❌ Saito asks Cobb can he do the job.
✅ Saito asks if Cobb can do the job.
A hidden yes/no question needs if or whether, and normal word order: Cobb can, not can he.
One more thing
This part is a little harder. You can come back to it later.
If can be confusing because it has two jobs. It can start a hidden question, but it can also start a condition. In writing, whether avoids this confusion. Compare the two sentences below: the first is about a condition that changes what happens next, while the second simply reports what the team wants to find out.
✅ Tell me if you see anything strange. (a condition: tell me when that happens)
✅ Tell me whether you see anything strange. (a question: yes or no, tell me)
Practice: choose the right word
Eight questions. Choose one word. You get the answer, and why.
1. ___ the plan is safe is not clear yet.
At the start of a sentence, only whether works.
2. Saito asks ___ Cobb can plant an idea.
This is a hidden yes/no question, so use if (or whether).
3. The team talks about ___ inception is possible.
After the preposition about, only whether works.
4. Ariadne has to decide ___ to join them.
Before to + verb, always use whether.
5. Cobb knows ___ the job will be dangerous.
This is a fact he is sure of, not a yes/no question, so use that.
6. Do you know ___ ?
A hidden question keeps normal word order: the dream will last, not will the dream last.
7. ___ or not Cobb agrees, Saito has made his offer.
Only whether can go right before or not.
8. Arthur wonders ___ Eames is the right person.
After wonder, if and whether are both correct.
Your turn
Choose one ending. Then listen to your sentence.
Every sentence here is correct. Pick the one that is true for you. Say it out loud too!
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