if or when

When we are using if or when in the sense of whenever, in other words to talk about repeated predictable actions, it doesn't matter which we use as there is very little difference in meaning. Compare the following:

• When I'm broke, I borrow money from my mother.
• I borrow money from my mother if I'm hard-up.
• Whenever I'm short of cash, I borrow money from my mother.

• I always feel sick if I go for a ride in your car.
• I always feel nauseous when I go for a ride in your car.
  I always feel queasy whenever I go for a ride in your car.

when not if

If it is certain that something has happened, is happening or will happen, we have to use when:

• When I arrived back home, Sandra was no longer there.
• You can have a drink when we get to Julie's place. Not now, when you're driving.

if not when

If it is uncertain that something has happened or will happen, we have to use if:

• He'll be here soon, if he caught the 1.30 train.
• If I manage to get to Argentina next year, I'll come and visit you.

It is in this sense that the meaning corresponds to in the event that or in case of. We sometimes use these expressions instead of if, if we wish to sound more formal. Compare the following:

• In the event that you are unable to fly on 1 May, I would advise you to buy a travel ticket with greater flexibility.
• What happens if you can't fly on 1 May? Don't buy a travel ticket which limits your options.
• In case of frost, the race meeting will be cancelled.
• If frost is forecast, the race meeting will be called off.
  

if or whether

Restrictions also operate in the use of if and whether. If and whether, of course, always imply uncertainty. You can generally use if or whether when you are reporting yes/no questions. It doesn't matter which you choose:

• Can you take care of Tommy for me?
  ~ I don't know yet whether / if I shall be able to look after Tommy during the Easter holidays or not.

• Is Paco still around?
• I wondered whether / if Paco had left the country as I hadn't seen him for some time.

whether not if

However, after prepositions, before to-infintives, in whether…or… constructions and whenever we start a sentence with the conjuntion, we have to use whether:

• Whether I'll get there in time for Henry's lecture, I don't know.
• I can't make up my mind whether to buy some new summer clothes now or wait until the prices go down..
• There was a lot of discussion about whether Ringo should have his tongue pierced or not.
• Whether we go by bus or by train doesn't really matter. It's bound to be a slow journey.
• I'm going to spend all of granny's money on a new kitchen whether you like it or not!

if not when in 'conditional' sentences

In 'conditional' sentences, we normally use if. If we are describing something which must happen first so that something else can occur, i.e. referring to a condition for something to happen, we have to use if, unless if means whenever. Consider these three conditional sentences below and then scroll back to the very first examples to remind yourself about if meaning whenever:

• I'll help you landscape the garden, if I can get off work for a couple of weeks.
• Don't take any chances. What would you do if you lost your job?
• If my dad had been alive, he would've sorted it all out for you in a matter of days.

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