Zero Conditional

What are conditionals in English grammar? Sometimes we call them 'if clauses'. They describe the result of something that might happen (in the present or future) or might have happened but didn't (in the past) . They are made using different English verb tenses.
They are used to express that the action in the main clause (without if) can only take place if a certain condition (in the clause with if) is fulfilled. "Condition" means "situation or circumstance". If a particular condition is true, then a particular result happens.

¨We use the Zero Conditional to express certainty about a future result.

Example:

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) Present Simple clause, Present Simple clause (result).  

(if + present simple, ... present simple)

Example:

If you heat water to 100 degrees Celsius, it boils. 

      

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.

Other examples:

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?

In Zero Conditional, we often use when instead of if, For example:

When I get up late, I miss my bus. When I am late for work, my boss gets angry.