Zero Conditional

for certainty

If you heat ice, it melts.

We use the so-called zero conditional when the result of the condition is always true, like a scientific fact.

Take some ice. Put it in a saucepan. Heat the saucepan. What happens? The ice melts (it becomes water). You would be surprised if it did not.

if condition result
  Present Simple Present Simple
If you heat ice, it melts.

Notice that we are thinking about a result that is always true for this condition. The result of the condition is an absolute certainty. We are not thinking about the future or the past, or even the present. We are thinking about a simple fact. We use the Present Simple tense to talk about the condition. We also use the Present Simple tense to talk about the result. The important thing about the zero conditional is that the condition always has the same result.

Look at these example sentences:

if condition result
  Present Simple Present Simple
If I miss the 8 o'clock bus, I am late for work.
If I am late for work, my boss gets angry.
If people don't eat, they get hungry.
If you heat ice, does it melt?
result if condition
Present Simple   Present Simple
I am late for work if I miss the 8 o'clock bus.
My boss gets angry if I am late for work.
People get hungry if they don't eat.
Does ice melt if you heat it?
We often use when instead of if, for example: When I get up late, I miss my bus.