Both if and whether can introduce a choice between two possibilities: "I do not know if she is coming" and "I do not know whether she is coming" mean the same thing.
The difference appears in fixed positions. After a preposition, whether is required: "It depends on whether we have time." Before a to-infinitive, whether is required: "I cannot decide whether to stay."
This page lists the positions where only whether works, shows where if is the natural choice, and finishes with a 20-question drill with a rule under every answer.
The rule
Both words report a yes or no question
- "I asked if the shop was open" and "I asked whether the shop was open" are both correct.
- The choice is between yes and no, so no question mark is needed in the reported form.
- After ask, know, wonder, remember and see, both words are common.
- If is more casual; whether sounds slightly more formal.
Whether after a preposition
- After a preposition, only whether is possible: "It depends on whether she agrees."
- "It depends on if she agrees" is not standard English.
- The same rule applies to about, of and in: "We talked about whether to move house."
- The pattern appears a lot in questions of choice: "There is no question of whether he can do it."
Whether before a to-infinitive
- Whether + to-infinitive expresses a choice about an action: "I cannot decide whether to take the job."
- If cannot be followed by to: "if to take the job" is wrong.
- The pattern works with know, wonder, decide and ask: "She wondered whether to call him."
- A full clause after whether works the same way: "whether she should call him".
Whether or not and if or not
- "Whether or not it rains, we will go" is the standard pattern at the start of a sentence.
- In the middle of a sentence, both work: "I will go whether or not it rains" and "I will go if it rains or not".
- If takes or not at the end of its clause, not directly after if: "if it rains or not", never "if or not it rains".
- After whether, or not can come straight away or at the end.
If means condition too
- If has a second job: it introduces conditions, and whether cannot do that job.
- "If you are late, we will start without you" is a condition, not a choice.
- In reported questions, if keeps the meaning of a yes or no question.
- When in doubt in a reported question, whether is always safe; in a condition, only if works.
Examples
- I do not know if the train is on time.Both words fit; if is the casual choice.
- I do not know whether the train is on time.Whether adds a slightly formal tone.
- It depends on whether we have enough money.After a preposition, only whether is correct.
- We discussed whether to stay another night.Whether takes a to-infinitive; if cannot.
- She wondered whether to send a message.Another whether + to pattern.
- Whether or not you agree, the plan will go ahead.Whether or not is standard at the start.
- I will go if it rains or not.With if, or not comes at the end of the clause.
- If you are late, we will start without you.Here if states a condition, not a choice.
- Ask him whether he has finished.Whether reports the yes or no question cleanly.
- I asked if she wanted coffee.If is natural after asked in speech.
Common mistakes
- Wrong: It depends on if we have time. Right: It depends on whether we have time.
- After a preposition, only whether is standard.
- Wrong: I cannot decide if to stay or leave. Right: I cannot decide whether to stay or leave.
- Whether takes a to-infinitive; if cannot be followed by to.
- Wrong: If or not the weather is good, we will go. Right: Whether or not the weather is good, we will go.
- At the start of a sentence, use whether or not, not if or not.
- Wrong: We talked about if the plan would work. Right: We talked about whether the plan would work.
- About is a preposition, so it needs whether.
- Wrong: Whether it rains, we will cancel the game. Right: If it rains, we will cancel the game.
- A condition uses if. Whether introduces a choice, not a condition.
Practice drill
Answer all 20 questions. Each answer is marked at once, and the rule is explained under the question.
I do not know ___ she will come to the party.
Show answer and explanation
Answer: A. if Both if and whether fit a reported yes or no question; if is the casual choice.
It depends on ___ the shop is open.
Show answer and explanation
Answer: B. whether After the preposition on, only whether is standard.
I cannot decide ___ to take the job.
Show answer and explanation
Answer: C. whether Whether takes a to-infinitive, and if cannot be followed by to.
We talked about ___ the plan would work.
Show answer and explanation
Answer: D. whether After the preposition about, whether is required.
___ or not it rains, the match will start.
Show answer and explanation
Answer: A. Whether At the start of a sentence, whether or not is the standard pattern.
She asked ___ I wanted tea or coffee.
Show answer and explanation
Answer: B. if If introduces the reported question about a yes or no choice; whether would also fit.
I wonder ___ he is at home.
Show answer and explanation
Answer: C. whether Whether introduces the reported question; if would also be correct.
___ you are late, we will start without you.
Show answer and explanation
Answer: D. If This is a condition, and only if marks a condition.
There is some doubt about ___ he can finish on time.
Show answer and explanation
Answer: A. whether After the preposition about, whether is the correct choice.
She wondered ___ to call him or wait.
Show answer and explanation
Answer: B. whether Whether + to-infinitive expresses the choice; if cannot take to.
Please tell me ___ the parcel has arrived or not.
Show answer and explanation
Answer: C. whether Whether pairs naturally with or not in this reported question; if is not among the options.
I asked him ___ he was feeling well.
Show answer and explanation
Answer: D. if If introduces the reported yes or no question; whether also fits.
The decision depends on ___ everyone agrees.
Show answer and explanation
Answer: A. whether On is a preposition, so the clause needs whether.
He could not remember ___ he had locked the door.
Show answer and explanation
Answer: B. whether Whether reports the doubt about a yes or no action; if also fits here.
I do not care ___ you are rich or poor.
Show answer and explanation
Answer: C. whether Whether pairs with the two options rich or poor.
___ she calls, tell her I am out.
Show answer and explanation
Answer: D. If This is a condition, so if is the correct word.
We are not sure ___ to go by train.
Show answer and explanation
Answer: A. whether The to-infinitive after the gap requires whether.
It is not clear ___ the museum is open today.
Show answer and explanation
Answer: B. whether Whether introduces the uncertain yes or no fact; if would also fit.
Think about ___ you really need the car.
Show answer and explanation
Answer: C. whether Think about needs the preposition about, so whether follows.
I will bring an umbrella ___ it rains.
Show answer and explanation
Answer: D. if The umbrella depends on the rain, so this is a condition with if.
Drill complete
You answered every question.
Next topic: Articles with school, hospital and bedTake the level test
Questions learners ask
Are if and whether interchangeable?
They are interchangeable in reported yes or no questions after verbs like ask, know and wonder: "I asked if she was ready" and "I asked whether she was ready" are both fine. They are not interchangeable after prepositions or before to-infinitives, where only whether works. If also has the separate job of marking a condition.
Why is "depends on if" wrong?
After a preposition, the object must be a noun phrase or a full clause introduced by whether. The clause "if she agrees" is a condition, not a noun clause in this position. English therefore requires whether: "It depends on whether she agrees."
Which is better in formal writing?
Whether is usually better in formal writing. It is never wrong in reported questions, and it handles prepositions and infinitives correctly. If is more conversational and can sound lighter. In a condition, of course, only if works.
More grammar topics
Articles with school, hospital and bed
No article when the place is used for its normal purpose; a or the when it is just a building or a specific one.
During vs while
During + noun answers when; while + subject and verb answers what else was happening at the same time.
By car, on foot, in a taxi: transport prepositions
By + vehicle for the way you travel, on or in + a/the + vehicle when you picture the journey, and the fixed phrase on foot.
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