Zero Conditional


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 are sure that you understand the lesson, you can continue with the exercises.