Zero conditional


INTRODUCTION
The zero conditional is a structure used for talking about general truths — things which always happen under certain conditions. This page will explain how the zero conditional is formed, and when to use it.
1. The structure of a zero conditional sentence
A zero conditional sentence consists of two clauses, an “if” clause and a main clause (In most zero conditional sentences you can use when or if and the meaning will stay the same.):
“if” clause
main clause
If you heat water to 100 degrees,
it boils.
If the “if” clause comes first, a comma is usually used. If the “if” clause comes second, there is no need for a comma:
main clause
“if” clause
Water boils
if you heat it to 100 degrees,
We use the same verb form in each part of a zero conditional: the simple present tense:
“if” clause
if + subject + simple present verb
main clause
subject + simple present verb
2. Using the zero conditional
The zero conditional is used to talk about things which are always true — such as scientific facts and general truths:
Example
Explanation
If you cross an international date line, the time changes.
This always happens — every time you cross a date line.
If it rains, the grass gets wet.
This is basically always true — the rain makes the grass wet.
Wood doesn’t burn if there is no air.
This is a scientific fact — wood needs air in order to burn. No air = no fire.
When you talk about things that are generally or always true, we can use:
If/When/Unless plus a present form plus present simple or imperative.
· If he gets there before me, ask him to wait.
· When you fly budget airline, you have to pay for your drinks and snacks.
· Unless you need more space, a small car is big enough for one person.
Note that we are not talking about a specific event but something which is generally true. In the condition clause, we can use a variety of present forms. In the result clause , there can only be the present simple or imperative.
· If you visit London, go on the London Eye.
· If unemployment is rising, people tend to stay in their present jobs.
· If you have done that, go and have a coffee.
· When I am concentrating , do not make so much noise
Note that ‘unless’ means the same as’ if not’
· Unless he asks you politely, refuse to do any more work on the project.
· Unless prices are rising, it is not a good investment.

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