If/Whether

Introduction

Sometimes if and whether are interchangeable, but not always. Here we explain the differences bewteen the two words and show you how to use if and whether in English.

The cake is so tasty that Henry and Isabella would like to eat it all!

If they eat the whole cake, there won’t be any left to give their friends later.

But Henry and Isabella don’t know if their friends are come or not.

They can’t decide whether or not to save some cake.

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If or Whether

Whether and if both indicate uncertainty. We use them in indirect questions and in certain fixed expressions.

Indirect Questions

Use if/whether in indirect questions. Whether is more formal than if.

Example:
Henry asked Isabella if they should save some cake.
Isabella asked whether their friends were coming.

For more information about indirect questions see indirect speech.

If/Whether … or not

We often use if/whether in a construction with or not. Whether is more common than if.

  • Use if/whether when or not comes at the end of the clause.
Example:
Henry and Isabella don’t know if their friends are coming or not.
Henry and Isabella don’t know whether their friends are coming or not.
  • Use whether when or not comes directly after whether.
Example:
Henry and Isabella don’t know whether or not their friends are coming. (but not:if or not)

Only If

  • Use if in conditional sentences.
Example:
If they eat the whole cake, there won’t be any to give their friends later.
(but not: Whether they eat the whole cake, there won’t be …)

For more information about conditional sentences see if–clauses.

Only Whether

  • Use whether before infinitives with to.
Example:
They can’t decide whether to save some cake for their friends.(but not: … if to save some cake)
  • Use whether after prepositions.
Example:
They aren’t sure about whether they should save some cake.(but not: … about if they should save some cake.)

For more information about preopositions or infinitives with to see Prepositions or Infinitive/Gerund.