The zero conditional

We can form a zero conditional sentence with two present simple verbs (one in the 'if clause' and one in the 'main clause'):

if + present simple, ... present simple

This conditional is used when the result will always happen.

If water reaches 100 degrees, it always boils.
It's a fact.

The result of the 'if clause' is always the main clause.

The 'if' in this conditional can usually be replaced by 'when' without changing the meaning.

For example:
If water reaches 100 degrees, it boils.
(It is always true)
If I eat peanuts, I am sick.
(This is true only for me, maybe, not for everyone, but it's still true that I'm sick every time I eat peanuts)

 

Here are some more examples:

zero conditional - extra exercise 1