Conditionals: Zero and First (If vs When)

Common Mistakes

If I see her, I tell her what you said.

If I see her, I will tell her what you said.

You will not pass the exam if you will not study.

You will not pass the exam if you do not study.

When you arrive late to a Keith Jarrett concert they don’t let you in.

If you arrive late to a Keith Jarrett concert, they don’t let you in.

I will call the police when she is not back within the next hour.

I will call the police if she is not back within the next hour.

When I decide to go to New York this year, I will certainly come and see you.

If I decide to go to New York this year, I will certainly come and see you.

If you mix red and green, you get brown.

If you arrive late at my company, no one says anything - it’s all very easy-going.

If I arrive late tomorrow, my boss will be very angry - we have a meeting early in the morning.

I won’t pass the exam if I don’t study.

When I see her, I will tell her. It will either be Monday or Tuesday next week.

If I see her, I will tell her. But to be honest I don’t see her very often so I can’t guarantee anything.

if + present + present (situations that never change, laws). Example: If you heat ice, it melts. In this case, you could replace if with when with little difference in meaning. This form is known as the zero conditional.

if + present + will (real hypothesis regarding now or the future). Examples: If it rains this weekend, I will stay at home. This form is known as the first conditional.

You can generally switch the two parts of the phrases around. Example: If you come to the party, I will be happy = I will be happy if you come to the party.

when is always used to introduce a real situation, not a hypothetical situation. Will means that the speaker thinks / assumes that something will certainly happen at some point (When I get home, I will call you immediately). In the example, I may not be sure exactly what time I will arrive home, but I know for sure that I am going home.

if introduces a possibility (If I get home before midnight, then I will call you, if not, I’ll call you tomorrow morning). In this example, I may or may not arrive home before midnight.

With the zero conditional (i.e. when making generalizations where the outcome is definite), there may be little difference in meaning between when and if e.g. Plants die if / when you don’t give them sufficient water.

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