Conditional Type 0

Once we have looked at the three main forms of conditional sentences (1, 2 and 3), we must bear in mind that there is another type of situation - one that is always true if something happens and this is what we call Conditional 0.

This use is similar to, and can usually be replaced by, a time clause using 'when' (example: When I am late, my friend takes the bus to the office.)

If I am late, he takes the bus to the office.
She doesn't cook dinner if I stay at work late.
If you heat water, it boils at 100 degrees.

Conditional 0 is formed by the use of the present simple in the if clause followed by a comma the present simple in the result clause.

You can also put the result clause first without using a comma between the clauses.

If he comes to town, we have dinner.
OR
We have dinner if he comes to town.

The main difference between the zero conditional and a future time clause with 'when' is that the zero conditional is for situations which don't happen on a regular basis. In other words, use future time clauses for routines, but use the zero conditional for exceptional situations. Notice how the zero conditional is used to underline that a situation does not regularly occur in the examples below.

Routines
We discuss sales when we meet on Fridays.
When she visits her father, she always brings a cake.

Exceptional Situations
If a problem occurs, we immediately send our repairman.
She informs her director if she can't deal with the situation herself.