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.

The structure of a zero conditional sentence

A zero conditional sentence consists of two clauses, an "if" clause and a main clause (note that most zero conditional sentences will mean the same thing if "when" is used instead of "if"):

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

Using the zero conditional

The zero conditional is used to talk about things which are always true -- scientific facts, general truths, and so on:

If you cross an international date line, the time changes.
This always happens, every time you cross a dateline.
If you go 10 meters under water, the pressure increases to two atmospheres.
This is basically always true -- the pressure of 10 meters of water equals one atmosphere.
Phosphorus burns if you expose it to air.
This is a scientific fact -- you can test it in a laboratory.