If v Whether

If and whether are both subordinating conjunctions and can often be interchanged. They both introduce a conditioner uncertainty  in meaning. However, there are a few rules that tell us when to use one or the other. 

Use Both

We can use if and whether in the following situations:

• Reported speech 

He asked if we could go to town.

He asked whether we could go to town. 

• When we’re not sure about something 

I don’t know if she’s coming to the meeting. 

I don’t know whether she’s coming to the meeting. 

In general, whether is used in more formal situations while if in more everyday situations. 

Use If

We can only use if in conditional sentences. 

If I were you, I would apologise. 

We will cancel the event if it rains. 

If I had woken earlier today, I would have had time fo breakfast. 

Use Whether

• After prepositions 

I’m not interested in whether you can come.

It depends on whether she replies. 

• Before to + infinitive

I can’t decide whether to take my coat. 

We’re still thinking about whether to put in an offer. 

• Phrase “or” / “or not” (two or more options)

I’d like to know whether to wait or stay. 

Please confirm whether we got the bid or not.