Difference Between If and Whether

Main Difference – If vs. Whether

If and whether are two conjunctions that should be used very carefully since the interchange of these two can sometimes result in a change of meaning. The most important fact to remember when you are using these two conjunctions is that if and whether are interchangeable in some cases, but not always. The main difference between if and whether is that if is always used in conditionals whereas whether can be used in all other instances expect conditionals. Let us first look at the instances where these two words can be used interchangeably, then move on to the difference between if and whether.

Interchangeability

If and whether can be used interchangeably in the following instances.

When writing yes/no questions in reported speech

“Are you going home?” he asked – He asked whether I am going home. or He asked if I am going home.

Or

I’m not sure if he is telling the truth or lies.

I’m not sure whether he is telling the truth or lies.

However, in this construction, using whether considered is more accepted and common.

If – Meaning and Usage

If is always used to introduce a condition. In a conditional sentence, a condition has to be completed in order for something to occur.

If you tell me the truth, I will help you.

If he had not lied, this would never have happened.

He will blame me if you something happens to you.

In addition, if is commonly used in indirect questions as well. As mentioned above, it is interchangeable with whether in such instances.

Call me if you are interested in buying this cottage.

Whether – Meaning and Usage

Whether should be always used in the following instances.

When there are two alternatives (Both alternatives should not be conditions.)

Let me know whether you need my car.

The 2 alternatives here are, Needing the car & not needing the car. Using if in this not grammatically incorrect. If whether is replaced with if in this sentence, the meaning would change. 

Let me know if you need my car.

This sentence is a conditional sentence since needing the car act as a condition.

After prepositions

I wanted to talk with you about whether your son is going to continue this class.

After infinitive verbs starting with to

I was not sure whether to tell him the truth.

At the beginning of a clause that functions as the subject or complement.           

Whether you pass or fail is not my concern.

She doesn’t care whether they love her or hate her.

It is always better to choose whether in a formal context.

Tell me whether they taste good.

Difference Between If and Whether

Condition

If is always used with conditions.

Whether is not used with conditions.

Prepositions

If is not used after prepositions.

Whether is used after a preposition.

Infinitive verbs

If is not used after an infinitive verb starting with to.

Whether is used after an infinitive verb starting with to.

Clauses

If is not used at the beginning of a clause that functions as the subject or complement.

Whether is used at the beginning of a clause that functions as the subject or complement.        

Two alternatives

If is not generally used in a sentence that presents two alternatives.

Whether is used when there are two alternatives.

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